Page 1
Solid State NMR
Bruker BioSpin
think
forward
AVANCE Solids
User Manual
Version
NMR Spectroscopy
002
Page 2
The information in this manual may be altered without notice.
BRUKER BIOSPIN accepts no responsibility for actions taken
as a result of use of this manual. BRUKER BIOSPIN accepts
no liability for any mistakes contained in the manual, leading to
coincidental damage, whether during installation or operation of
the instrument. Unauthorized reproduction of manual contents,
without written permission from the publishers, or translation
into another language, either in full or in part, is forbidden.
This manual was written by:
Hans Foerster, Jochem Struppe, Stefan Steuernagel, Fabien Aussenacc,
Francesca Benevelli, Peter Gierth, and Sebastian Wegner
Desktop Published by:
Stanley J. Niles
© May 25, 2009: Bruker Biospin GmbH
Rheinstetten, Germany
P/N: Z31848
DWG-Nr.: Z4D10641 002
For further technical assistance on Solid State NMR, please do
not hesitate to contact your nearest BRUKER dealer or contact
us directly at:
BRUKER BioSpin GMBH
am Silberstreifen
D-76287 Rheinstetten
Germany
Phone: + 49 721 5161 0
FAX: + 49 721 5171 01
E-mail: solids@bruker.de, service@bruker.de
Internet: www.bruker.com
Page 3
Contents
Contents ............................................................................................... 3
1 Introduction ........................................................................................... 9
1.1 Disclaimer .................................................................................................................... 10
1.2 Safety Issues ............................................................................................................... 10
1.3 Contact for Additional Technical Assistance .................................................................. 10
2 Test Samples ........................................................................................11
3 General Hardware Setup ..................................................................... 15
3.1 Connections to the Preamplifier .................................................................................... 15
3.2 RF Connections Between Preamplifier and Probe ......................................................... 20
3.3 RF-Filters in the RF Pathway ........................................................................................ 21
3.4 Connections for Probe Identification and Spin Detection ............................................... 25
3.5 MAS Tubing Connections ............................................................................................. 26
3.5.1 Connections ..................................................................................................................27
Wide Bore (WB) Magnet Probes ...............................................................................28
Standard Bore (SB) Magnet Probes ..........................................................................30
3.6 Additional Connections for VT Operation ...................................................................... 31
3.7 Probe Setup, Operations, Probe Modifiers .................................................................... 41
3.7.1 Setting the Frequency Range of a Wideline (single frequency) Probe ............................41
3.7.2 Shifting the Probe Tuning Range ...................................................................................42
3.7.3 Adding a Frequency Channel to a Probe (WB probes only) ............................................48
3.8 Mounting the Probe in the Magnet/Shim Stack .............................................................. 50
3.9 EDASP Display: Software Controlled Routing ............................................................... 51
4 Basic Setup Procedures ...................................................................... 55
4.1 General Remarks ......................................................................................................... 56
4.2 Setting the Magic Angle on KBr .................................................................................... 57
4.2.1 RF-Routing ...................................................................................................................57
4.2.2 Setting Acquisition Parameters ......................................................................................59
4.3 Calibrating 1H Pulses on Adamantane .......................................................................... 65
4.4 Calibrating 13C Pulses on Adamantane and Shimming the Probe ................................. 73
4.5 Calibrating Chemical Shifts on Adamantane ................................................................. 75
4.6 Setting Up for Cross Polarization on Adamantane ........................................................ 76
4.7 Cross Polarization Setup and Optimization for a Real Solid: Glycine ............................. 79
4.8 Some Practical Hints for CPMAS Spectroscopy ............................................................ 85
4.9 Field Setting and Shift Calibration ................................................................................ 87
4.10 Literature ..................................................................................................................... 88
5 Decoupling Techniques ...................................................................... 89
5.1 Heteronuclear Decoupling ............................................................................................ 89
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Contents
5.1.1 CW Decoupling ............................................................................................................. 89
5.1.2 TPPM Decoupling ......................................................................................................... 90
5.1.3 SPINAL Decoupling ...................................................................................................... 91
5.1.4 Swept-Frequency-TPPM ............................................................................................... 91
5.1.5 XiX Decoupling ............................................................................................................. 91
5.1.6 Pi-Pulse Decoupling .....................................................................................................91
5.2 Homonuclear Decoupling ............................................................................................. 92
5.2.1 Multiple Pulse NMR: Observing Chemical Shifts of Homonuclear Coupled Nuclei .......... 92
5.2.2 Multiple Pulse Decoupling ............................................................................................. 92
BR-24, MREV-8, BLEW-12 ....................................................................................... 92
FSLG Decoupling ..................................................................................................... 92
DUMBO ................................................................................................................... 97
5.3 Transverse Dephasing Optimized Spectroscopy ........................................................... 98
6 Practical CP/MAS Spectroscopy on Spin 1/2 Nuclei ...........................99
6.1 Possible Difficulties ...................................................................................................... 99
6.2 Possible Approaches for 13C Samples ......................................................................... 99
6.3 Possible Approaches for Non-13C Samples ............................................................... 101
6.4 Hints, Tricks, Caveats for Multi-nuclear (CP-)MAS Spectroscopy ................................ 102
6.5 Setup for Standard Heteronuclear Samples 15N, 29SI, 31P ....................................... 102
7 Basic CP-MAS Experiments ............................................................... 105
7.1 Pulse Calibration with CP .......................................................................................... 105
7.2 Total Sideband Suppression TOSS ............................................................................ 106
7.3 SELTICS ................................................................................................................... 110
7.4 Non-Quaternary Suppression (NQS) .......................................................................... 113
7.5 Spectral Editing Sequences: CPPI, CPPISPI and CPPIRCP ....................................... 116
8 FSLG-HETCOR ...................................................................................119
8.1 Pulse Sequence Diagram for FSLG HETCOR ............................................................ 120
8.2 Setting up FSLG HETCOR ......................................................................................... 121
8.3 Results ...................................................................................................................... 125
9 Modifications of FSLG HETCOR ........................................................127
9.1 Carbon Decoupling During Evolution .......................................................................... 128
9.2 HETCOR with DUMBO, PMLG or w-PMLG, Using Shapes .......................................... 129
9.2.1 The Sequence pmlghet ............................................................................................... 129
9.2.2 w-pmlghet ................................................................................................................... 132
9.2.3 edumbohet ................................................................................................................. 133
9.2.4 dumbohet ................................................................................................................... 134
9.3 HETCOR with Cross Polarization under LG Offset ..................................................... 135
10 RFDR ..................................................................................................137
10.1 Experiment ................................................................................................................ 138
10.2 Set-up ....................................................................................................................... 138
10.3 Data Acquisition ........................................................................................................ 139
10.3.1 Set-up 2D Experiment ................................................................................................. 139
10.4 Spectral Processing ................................................................................................... 141
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Contents
11 Proton Driven Spin Diffusion (PDSD) ................................................143
11.1 Pulse Sequence Diagram ........................................................................................... 145
11.2 Basic Setup ................................................................................................................ 145
11.2.1 2D Experiment Setup .................................................................................................. 146
11.3 Acquisition Parameters .............................................................................................. 147
11.3.1 Processing Parameters ...............................................................................................149
11.4 Adjust the Rotational Resonance Condition for DARR/RAD ........................................ 149
11.5 Example Spectra ........................................................................................................ 151
12 REDOR ................................................................................................155
12.1 Pulse Sequence ......................................................................................................... 157
12.2 Setup ......................................................................................................................... 157
12.2.1 Data Acquisition ..........................................................................................................159
12.2.2 Data Processing .......................................................................................................... 160
12.3 Final Remarks ............................................................................................................ 167
13 SUPER ................................................................................................169
13.1 Overview .................................................................................................................... 169
13.2 Pulse Program ........................................................................................................... 170
13.3 2D Experiment Setup ................................................................................................. 170
13.3.1 Experiment setup ........................................................................................................170
13.3.2 Setup 2D Experiment ..................................................................................................171
13.4 Data Acquisition ......................................................................................................... 173
13.5 Spectral Processing ................................................................................................... 174
14 Symmetry Based Recoupling .............................................................179
14.1 Pulse Sequence Diagram, Example C7 ...................................................................... 181
14.2 Setup ......................................................................................................................... 181
14.2.1 Spectrometer Setup for 13C ........................................................................................183
14.2.2 Setup for the Recoupling Experiment ..........................................................................183
14.2.3 Setup of the 2D SQ-DQ Correlation Experiment ..........................................................185
14.3 Data Acquisition ......................................................................................................... 186
14.4 Spectral Processing ................................................................................................... 188
14.5 13C-13C Single Quantum Correlation with DQ Mixing ................................................ 189
14.6 Data Acquisition ........................................................................................................ 190
14.7 Spectral Processing ................................................................................................... 191
15 PISEMA ...............................................................................................193
15.1 Pulse Sequence Diagram ........................................................................................... 194
15.2 Setup ......................................................................................................................... 195
15.3 Processing ................................................................................................................. 198
16 Relaxation Measurements ..................................................................201
16.1 Describing Relaxation ................................................................................................ 201
16.2 T1 Relaxation Measurements ..................................................................................... 202
16.2.1 Experimental Methods .................................................................................................202
16.2.2 The CP Inversion Recovery Experiment ......................................................................203
16.2.3 Data Processing .......................................................................................................... 205
16.2.4 The Saturation Recovery Experiment ..........................................................................208
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16.2.5 T1p Relaxation Measurements .................................................................................... 209
16.3 Indirect Relaxation Measurements ............................................................................. 210
16.3.1 Indirect Proton T1 Measurements ............................................................................... 211
17 Basic MQ-MAS .................................................................................... 213
17.1 Introduction ............................................................................................................... 213
17.2 Pulse sequences ....................................................................................................... 213
17.3 Data Acquisition ........................................................................................................ 215
17.3.1 Setting Up the Experiment .......................................................................................... 215
17.3.2 Two Dimensional Data Acquisition .............................................................................. 220
17.4 Data processing ......................................................................................................... 222
17.5 Obtaining Information from Spectra ............................................................................ 225
18 MQ-MAS: Sensitivity Enhancement ...................................................231
18.1 Split-t1 Experiments and Shifted Echo Acquisition ...................................................... 231
18.2 Implementation of DFS into MQMAS Experiments ...................................................... 233
18.2.1 Optimization of the Double Frequency Sweep (DFS) ................................................... 233
18.2.2 2D Data Acquisition .................................................................................................... 238
18.2.3 Data Processing .........................................................................................................240
18.3 Fast Amplitude Modulation - FAM .............................................................................. 242
18.4 Soft Pulse Added Mixing - SPAM ............................................................................... 242
19 STMAS ................................................................................................245
19.1 Experimental Particularities and Prerequisites ............................................................ 245
19.2 Pulse Sequences ....................................................................................................... 247
19.3 Experiment Setup ...................................................................................................... 249
19.3.1 Setting Up the Experiment .......................................................................................... 249
19.3.2 Two Dimensional Data Acquisition .............................................................................. 251
19.4 Data Processing ........................................................................................................ 253
20 Double-CP ..........................................................................................255
20.1 Pulse Sequence Diagram, Double CP (DCP) ............................................................. 256
20.2 Double CP Experiment Setup ..................................................................................... 256
20.2.1 Double CP 2D Experiment Setup ................................................................................ 256
20.2.2 15N Channel Setup .................................................................................................... 258
20.2.3 Setup of the Double CP Experiment ............................................................................ 259
20.2.4 Setup of the 2D Double CP Experiment ...................................................................... 264
20.3 2D Data Acquisition ................................................................................................... 265
20.4 Spectral Processing ................................................................................................... 266
20.5 Example Spectra ....................................................................................................... 267
21 CRAMPS: General .............................................................................. 271
21.1 Homonuclear Dipolar Interactions .............................................................................. 271
21.2 Multiple Pulse Sequences .......................................................................................... 271
21.3 W-PMLG and DUMBO ............................................................................................... 272
21.4 Quadrature Detection and Chemical Shift Scaling ...................................................... 273
22 CRAMPS 1D ........................................................................................275
22.1 Pulse Sequence Diagram of W-PMLG or DUMBO ...................................................... 275
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Contents
22.2 Pulse Shapes for W-PMLG and DUMBO ..................................................................... 276
22.3 Analog and Digital Sampling Modi .............................................................................. 277
22.3.1 Analog Mode Sampling ............................................................................................... 278
22.3.2 Digital Mode Sampling ................................................................................................278
22.4 Setup ......................................................................................................................... 279
22.5 Parameter Settings for PMLG and DUMBO ................................................................ 279
22.6 Fine Tuning for Best Resolution .................................................................................. 281
22.7 Fine Tuning for Minimum Carrier Spike ....................................................................... 281
22.8 Correcting for Actual Spectral Width ........................................................................... 281
22.9 Digital Mode Acquisition ............................................................................................. 282
22.10 Examples ................................................................................................................... 282
23 Modified W-PMLG ...............................................................................285
23.1 Pulse Sequence Diagram for Modified W-PMLG ......................................................... 285
23.2 Pulse Shapes for W-PMLG ......................................................................................... 286
23.3 Setup ......................................................................................................................... 287
23.4 Parameter Settings for PMLG and DUMBO ................................................................ 287
23.5 Fine Tuning for Best Resolution .................................................................................. 288
23.6 Correcting for Actual Spectral Width ........................................................................... 288
23.7 Digital Mode Acquisition ............................................................................................. 289
24 CRAMPS 2D ........................................................................................291
24.1 Proton-Proton Shift Correlation (spin diffusion) ........................................................... 291
24.2 Pulse Sequence Diagram ........................................................................................... 292
24.3 Data Processing ......................................................................................................... 293
24.4 Examples ................................................................................................................... 294
24.5 Proton-Proton DQ-SQ Correlation .............................................................................. 296
24.6 Pulse Sequence Diagram ........................................................................................... 297
24.7 Data Processing ......................................................................................................... 299
24.8 Examples ................................................................................................................... 299
A Appendix ........................................................................................... 303
A.1 Form for Laboratory Logbooks .................................................................................... 303
Figures ............................................................................................... 309
Tables ................................................................................................ 315
Index .................................................................................................. 319
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Contents
8 BRUKER BIOSPIN User Manual Version 002
Page 9
Introduction 1
This manual is intended to help the users set up a variety of different experiments
that are nowadays more or less standard in solid state NMR.
Previously, the manuals described the hardware in some detail, and also basic
setup procedures. Armed with this knowledge, it was assumed the users would be
in a position to manage the setup of even complicated experiments themselves.
In this manual however, the hardware is not discussed in detail, since there is no
longer much hardware which is specific to solid-state NMR. There are still trans
mitters with higher power, and preamps and probes that take this power, but for
the purposes of experimental setup, detailed knowledge is not required, since the
setup does not generally depend on the details of the hardware. So, this manual
is now much more specific to the type of experiment which is to be executed, and
includes tricks and hints required to set the experiment up properly for best perfor
mance. If any special hardware (or software) knowledge is required, it is indicated
within the experimental section.
This manual begins with the most frequently used solid-state NMR experiments,
and will be extended as time permits and as it is required by new development in
NMR. The manual is written primarily for Bruker AVANCE III instruments, but the
experimental part will be identical, or similar, for AVANCE I and AVANCE II instru
ments. For example, pulse programs will have slightly different names, differing
usually in the pulse program name extension. Contact your nearest applications
scientist if you do not find the experiment/pulse program that you are looking for.
Users of older instruments (DSX, DMX, DRX) should refer to the Solids Users
Manual delivered within the Help system at Help -> Other topics -> Solids Users
Manual. Even though the pulse programs may look similar, they will not run on
these instruments.
1
-
-
-
The first five chapters deal with basic setup procedures, subsequent chapters are
dedicated to specific types of experiments. There may be many different „sub“ ex
periments within a given type, since the same information can often be obtained
with pulse sequences differing by subunits only, or in using a totally different prin
ciple. The experiments outlined here are usually the most important ones and/or
the ones that were common at the time when the manual was written.
New chapters will be added, as the manual consists of largely self-contained units
rather than being a comprehensive single volume. This was done in order to be
more flexible in updating/replacing individual chapters. So do not be surprised if
some chapters are still missing, they will be completed in the near future and im
plemented as they are finished and proofread. The individual chapters are written
by different people, so there will be some differences in style and composition.
Note Concerning Future TopSpin Release
Upon the release of this manual, a new TopSpin version was in development. In
the new version, which is scheduled to be released later this year, there are fairly
big changes that will influence all of the setup routines described in this manual.
User Manual Version 002 BRUKER BIOSPIN 9 (327)
-
-
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Introduction
In the future version of TopSpin there will be a different way of setting pulse powers. There will be a watt scale which refers to the pulse power in watts. This allows you to set pulse powers in a spectroscopically more relevant scale.
Moreover, different transmitters and different routings will not anymore have an in
fluence on the pulse power setting, since it is referenced to an absolute, not relative scale. This means however, that some setup routines within this manual will
have to be modified to comply with this. The setting will also be possible on a dB
scale, however with an absolute reference. Power level changes will therefore be
calculated properly using calcpowlev. Where pulse power recommendations are
given in this manual, they will still apply if given in watts, they will however not ap
ply in the future version of TopSpin if given in dB.
We will try to release a new version of this manual when the new TopSpin version
is available, whereas possible inconsistencies will be removed. There is no incon
sistency with TopSpin vs. 2.1.
Disclaimer 1.1
Any hardware units mentioned in this manual should only be used for their intended purpose as described in their respective manual. Use of units for any purpose
other than that for which they are intended is taken only at the users own risk and
invalidates any and all manufacturer warranties.
-
-
-
Service or maintenance work on the units must be carried out by qualified
personnel.
Only those persons schooled in the operation of the units should operate
the units.
Read the appropriate user manuals before operating any of the units mentioned.
Pay particular attention to any safety related information.
Safety Issues 1.2
Please refer to the corresponding user manuals for any hardware mentioned in
this manual for relevant safety information.
Contact for Additional Technical Assistance 1.3
For further technical assistance please do not hesitate to contact your nearest
BRUKER dealer or contact us directly at:
BRUKER BioSpin GMBH
am Silberstreifen
D-76287 Rheinstetten
Germany
Phone: + 49 721 5161 0
FAX: + 49 721 5171 01
E-mail: service@bruker.de
Internet: www.bruker.de
10 (327) BRUKER BIOSPIN User Manual Version 002
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Test Samples 2
Table 2.1. Setup Samples for Different NMR Sensitive Nuclei
Nucleus Sample Method O1P Remarks
3
H
1
H Silicone paste
Silicone rubber
Adamantane
Glycine
Malonic Acid
19
F PVDF
PTFE
3
He
203,209
Tl
31
P (NH4)H2PO
7
Li LiCl MAS
117,119
Sn Sn (cyclohexyl)
Sm2Sn2O7/SnO
87
Rb RbNO3, RbClO
11
B BN
Boric Acid
65
Cu Cu-metal powder wideline knight shift +2500ppm
71
Ga Ga2O
129
Xe as hydroquinon
Clathrate
gas in air
23
Na Na2HPO
Na3P3O
51
V NH4VO
123
Te
27
Al AlPO-14 MQMAS 0 d1 05-1s, 4 lines
4
3
4
9
4
1
HMAS
1
HMAS
1
HMAS
CRAMPS
CRAMPS
19F
MAS
CP
19
FMAS
1H/31
PCP 0 powdered sample, piezoelectric, 4s
CP
4
MAS
2
MQMAS 0 0.5s repetition
4
MAS
MQMAS >5s repetition
hahn echo CT 300 kHz wide
CPMAS 0
MQMAS
MQMAS
0
0
0
-3
-3
106
126
0
0 dep. on crystal water 2-5 lines
setup proton channel, shim, set field
setup proton channel, set field
setup proton channel, set field, shim
under CRAMPS conditions
setup CRAMPS
resolution CRAMPS, d1=60s
direct observe 19F
CP 1H/19F, 1H/13C,19F/13C (low sensitivity)
direct observe
5ms contact, d1>10s
VT shift thermometer, d1<1s
Sm2Sn2O7,>60s SnO2 (temp. independent)
d1>5s
single pulses overnight, 1s
2
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Test Samples
Table 2.1. Setup Samples for Different NMR Sensitive Nuclei
13
C Adamantane
α-glycine
79
Br KBr MAS 57 d1< 50msec, angle setting
59
Co Co(CN)
55
Mn KMnO
93
Nb
207
Pb PbNO
Pb(p-tolyl)
29
Si Q8M
6
4
3
4
8
DSS,TMSS
77
Se H3SeO
(NH4)2SeO
113
Cd Cd(NO3)2*4H2O CPMAS 350 15ms contact, d1>8s
195
Pt K2Pt(OH)
199
Hg Hg(acetate)
3
4
6
2
Hexakis (dimethyl
sulphoxide)
Hg(II) trifluoromethansulfonate
2
H d-PMMA
d-PE
d-DMSO
6
Li LiCl, Li (org.) make sure it is not 6Li depleted, d1>60s
17
O D2O 0 pulse determination, 100scans,0.5s
15
N α-glycine CP 50 sensitivity, 4ms contact,4s
35
Cl KCl WL,MAS 0 pulse determ., 100 scans
33
S K2S MAS 0 100 scans in a >=500 MHz instr.
14
N NH4Cl MAS,WL 0 100 scans, narrow line.
25
Mg
47/49
Ti Anatas MAS
39
K KCl MAS,WL 0 100 scans
2
CP,DEC
CP
50
110
HH setup, shim
sensitivity,decoupling.Prep.: precipitate
with acetone from aq. solution, C,N fully
labelled for fast setup, recoupling, REDOR
(10% in natrl. abundance)
finely powdered, reduced volume
MAS shift thermometer
MAS >500 kHz pattern
MAS
shift thermometer, 0,753 ppm/degr.
d1>10s
CP -150
CPMAS
CPMAS
CPMAS
CPMAS
-50
0
1800
-200
5ms, 15s
d1>5s, reference sample 12.6/-108 ppm
reference sample 0 ppm
HH setup, 8ms contact, d1>10s
3ms, d1>4s
CPMAS -12000 1ms contact, d1>4s
CPMAS 2500
-2313
WL
WL
0
0
5ms contact, d1>10s
30-35ms contact, d1>10s *
wideline setup d1 5s
wideline setup d1 0.5s/10s amorphous/
crystalline
WL
0
exchange expt. at 315K
labelled for fast setup
12 (327) BRUKER BIOSPIN User Manual Version 002
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Test Samples
Table 2.1. Setup Samples for Different NMR Sensitive Nuclei
109
Ag AgNO
89
Y Y(NO3)3*6H2O CPMAS -50 10ms contact, d1>10s
3
AgSO3CH
3
* Literature: J.M. Hook, P.A.W. Dean and L.C.M. van Gorkom, Magnetic Resonance in Chemistry, 33, 77
(1995).
MAS
CPMAS 70
1scan, 500s, finely powdered
50 ms contact, 10 s repetition, 1 scan.
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Test Samples
14 (327) BRUKER BIOSPIN User Manual Version 002
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General Hardware Setup 3
Avance instruments are constructed in a way to minimize the requirements to reconnect or readjust hardware for different experiments. Probe changes are however sometimes necessary, and require some manual operations. This chapter
deals with connections that need to be done by the operator, and also with other
manipulations that are required to set up the instrument in an optimum way.
Since the RF pathways are under software control up to the preamplifier, and under operator control between preamplifier and probe, both setups are considered
separately.
All remaining connections (heater cable, thermocouple, gas flow, spin rate cable,
PICS cable) can in no way be under software control, so the operator is responsible for proper wiring, cabling, and tubing! Since mistakes (especially in connection
with compressed gas tubing) may cause rather expensive repairs, it is recommended to check carefully before an experiment is started.
The following operations will be described and illustrated with suitable images, for
WB and SB probes, where non-trivial differences exist.
3
"
Connections to the Preamplifier" on page 15
"RF Connections Between Preamplifier and Probe" on page 20
"RF-Filters in the RF Pathway" on page 21
"Connections for Probe Identification and Spin Detection" on page 25
"MAS Tubing Connections" on page 26
"Additional Connections for VT Operation" on page 31
"Probe Setup, Operations, Probe Modifiers" on page 41
"Mounting the Probe in the Magnet/Shim Stack " on page 50
"The edasp Display for a System with two Receiver Channels" on page 54
Connections to the Preamplifier 3.1
For solids and liquids there should normally be different sets of preamplifiers. Liquids preamplifiers (HPPR, High Performance Preamplifiers) are not suitable for
some of the requirements of solid state NMR. Where CP/MAS applications are the
only solids applications, it is however possible to use liquids preamplifiers for Xobservation. Solids preamplifiers (HPHPPr, High Power High Performance Pre-
amplifiers) are definitely required if high power ≥ 1 kW is used (liquids preamplifiers take max. 500W for X frequencies, 50W for proton and fluorine frequency).
For the high frequency range
are available, the older HPHPPr
19
F and 1H, two different types of solids preamps
19
F /1H and the recent replacement HPLNA
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General Hardware Setup
RF cables from transmitter, RS-485
control, DC voltages in, tune and lock
RF in, RF signal out to receiver, gate
pulses for preamplifier control (multireceive setup only).
The orange colored cable is the high
voltage supply for the HPLNA preamplifier.
(High Power Low Noise Amplifier) which is strictly frequency selective, either 19F
1
or
H.
The connections into (the back) of the preamp stack should normally not be
changed. For broadband high power preamplifiers, it is important to insert the appropriate “matching box” into the side of the preamp.
Figure 3.1. All Connections to the Back of the Preamplifier
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Connections to the Preamplifier
The lock preamplifier is located at the
bottom of the stack, the transmitter
cable carries the lock pulses. For solids, this preamp is normally not required.
When the transmitter cables are rewired to different preamp modules,
the changes must be entered into the
edasp routing (type edasp setpreamp, NMRSU password required).
Figure 3.2. Transmitter Cables (only) Wired to Back of the Preamplifier
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General Hardware Setup
Figure 3.3. The edasp setpreamp Display
Note for Figure 3.3.
nections!
: Transmitter to preamplifier wiring must reflect hardware con-
18 (327) BRUKER BIOSPIN User Manual Version 002
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Connections to the Preamplifier
1
1. RF signal out to receiver
2. Lock signal out to lock receiver
3. Tune RF in (from SGU 2 aux out)
4. PICS probe ID cable to probe
5. ATMA and AUX connectors
6. RS 485 control connection and DCin
7. Additional DC supply for >3 preamps
8. High voltage DC for HPLNA-preamp
9. Additional controls for multi-receiver
2
3
4
5
6
8
9
7
Figure 3.4. Additional Connections to the Preamplifier Stack.
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General Hardware Setup
1. Pulse from TX
2. Pulse pathway to probe
3. To probe
4. Signal from probe
5. Signal to preamplifier
1
2
3
4
5
2
4
Figure 3.5. Matching Box Setup for High Power X-BB Preamplifiers
The frequency of the observed nucleus must be within the bandwidth of the
matching box (the matching box contains a low pass filter to suppress frequencies
above the X-nucleus frequency range (
which directs the RF pulse into the probe, and the NMR signal into the preamplifier). High resolution preamplifiers use actively switched pin diodes for this purpose
and are therefore broadbanded, so there is no exchangeable box.
Pulsing with high power into an RF circuit which is not properly set up to pass this
frequency may result in damage to the RF circuit (in this case, the “matching box”)
or to the transmitter. This applies to filters, preamplifiers and matching boxes. Especially, if liquids preamps are used for solids work, as well power limitations as
frequency limitations must be strictly observed!
1
H, 19F) and a passive diode multiplexer,
RF Connections Between Preamplifier and Probe 3.2
These connections must be done with high quality cable, with suitable length. It
should be short, but not too short so that the cable must not be severely bent.
Higher quality cable is fairly stiff; the flexible ones are of less quality.
N.B.: It is extremely important that RF cables are not bent to a radius of less than
30 cm, and that no force is exerted on the RF connectors. Adapters should be
avoided; since every connector may change the impedance to deviate from the
required 50 Ω. Cables with loose connectors should be discarded, unless they
20 (327) BRUKER BIOSPIN User Manual Version 002
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RF-Filters in the RF Pathway
can be repaired by a skilled RF engineer. BNC connectors should be avoided;
they are usually off 50 Ω.
As pulses in solids NMR can be rather long, and rather high power, it is also necessary to consider the preamplifier’s power limitations.
Proton high resolution preamps are unsuitable for high power pulses, especially
for durations required for decoupling. High resolution X-BB preamplifiers are limited to 10 msec pulses at 300 (500) watts. If the back label does not say 500W, it is
300W max.
1H/19
F high power preamps need not necessarily be bypassed, but may gradually
deteriorate under many decoupling pulses. It is therefore recommended to bypass
these for decoupling unless the experiment requires that the preamp remain in
line.
Warning: These preamps are not optimized for 19F, so 19F decoupling
should never be done through this preamp.
1
H HPLNA preamplifiers need not be bypassed. HPLNA preamplifiers are
strictly frequency selective; a 19F pulse through a 1H HPLNA will destroy it!
RF-Filters in the RF Pathway 3.3
RF filters are frequently required if more than one frequency is transmitted to the
probe.
Without filtering, the noise and spurious outputs from the transmitter of one channel would severely interact with signal detection on another channel. One has to
keep in mind that pulse voltages are in the order of hundreds of volts, but NMR
signals are in the order of microvolt. In High Resolution, where the selection of nuclei to run is rather limited, it is possible to apply the necessary filtering inside the
preamplifier. For solids, this is not easily possible, due to the wide range of possible detection frequencies, but also due to the additional dead time that filters may
cause. So all filtering is done with external filters. If a single channel NMR experiment is run, no filters are required.
Usually, one filter per RF channel is required. Both filters should mutually exclude
the frequency of the other channel(s). Usual attenuations of the frequency to be
suppressed should be around > 80 dB, in special cases, when both frequencies
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General Hardware Setup
are rather close, >140 dB may be necessary (as in the case 1H/19F). More than
90 dB is usually hard to achieve with one filter.
Using external filters has three principal safety aspects:
1. Make sure you do not pulse into a filter with a frequency that this filter does not
pass.
2. Make sure the pulse power you apply does not exceed the power rating of this
filter. Most modern Bruker filters will survive 1 kW pulses of 5msec, but older filters (or non-Bruker filters) may not.
3. Remember that filters may attenuate the pulse RF voltage by as much as 1.5
dB (about 20%!)
The following figures illustrate the most common filter combinations.
Figure 3.6. Standard Double Resonance CP Experiment, Bypassing the Proton
Preamp
Figure 3.7. Standard CP Experiment, Proton Preamp in Line
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RF-Filters in the RF Pathway
Please note in Figure 3.7.
the preamp.
Figure 3.8. Triple Resonance Experiment, without X-Y Decoupling
Figure 3.8.
pass will suffice), note the preamp configuration. It is recommended not to put two
preamps of the same kind next to each other in order to avoid incorrect wiring of
probe and filters. For the X-channel, only the proton frequency needs to be filtered
out if X or Y is not decoupled while Y or X is observed (protons are usually decoupled).
is a triple resonance experiment, without X-Y decoupling (one band-
: Only high power preamps allow decoupling through
Figure 3.9. Triple Resonance Experiment, with X-Y Decoupling
Figure 3.9.
es required! Care should be taken that the two bandpass filters mutually exclude
the other frequency as efficiently as possible. Low pass filters will not allow X or Y
observe while Y or X is decoupled!).
User Manual Version 002 BRUKER BIOSPIN 23 (327)
is a triple resonance experiment, with X-Y decoupling (two band pass-
Page 24
General Hardware Setup
Figure 3.10. Triple Resonance 1H/19F-Experiment
Figure 3.10.
1
and
H decoupling or X-observation with 19F and 1H decoupling (WB probes ≥
400 MHz only! For SB probes and <400 MHz different hardware is used). A set of
1
H-transmitter/bandpass/preamp and 19F-transmitter/bandpass/preamp is re-
is a double/triple resonance HF-experiment, with 19F observation
quired.
Note: a standard
short pulses it is ok, for decoupling it must be bypassed, or a dedicated
1H/19
F preamplifier will not allow long 19F pulses through it! For
19
F pre-
amp must be used.
Figure 3.11. 19F/1H Combiner/Filter Set
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Connections for Probe Identification and Spin Detection
1. PICS probe connector
2. Spin rate monitor cable
Figure 3.12. Quadruple Resonance HFXY Experiment (WB probes ≥ 400 MHz
only!)
Connections for Probe Identification and Spin Detection 3.4
Most solids probes were delivered without Probe Identification System (PICS).
Probes delivered since 2007 are equipped with PICS. Please refer to Figure 3.4.
to identify the PICS port at the preamplifier cover module. The probe connections
for the spin rate cable and the PICS cable are shown in Figure 3.13.
in Figure 3.14.
for a SB probe.
for a WB and
User Manual Version 002 BRUKER BIOSPIN 25 (327)
Figure 3.13. PICS Probe Connector and Spin Rate Monitor Cable on a WB Probe
Page 26
General Hardware Setup
On SB probes the location may differ, but the connectors are (if present in the
case of PICS) easily identified by the type of connector.
Figure 3.14. Spin Rate Monitor Cable Connector for 2 Different Types of SB
Probes
Warning: The spin rate monitor cable has a probe side connector that is exactly the same as the power supply cable for the B-TO thermocouple oven
used with many high resolution probes. If this cable is connected to the
spin rate monitor assembly at the probe, the latter will be destroyed. Make
sure the B-TO cable and the MAS cable (labelled “probe” at the probe side)
are labelled such that they cannot be mistaken!
MAS Tubing Connections 3.5
For any type of fast spinning probe, compressed gas is used to provide the spinner bearing and drive gas. Please refer to the installation or site planning manuals
to learn about the gas requirements. The most important parameters are:
• Mains pressure (should be at least maximum required pressure +1 bar, to pro-
vide pressure regulation range).
• Bearing pressure: up to 4.5 bar (as of February 2008)
• Drive pressure: up to 4.5 bar (as of February 2008)
This means that at least 5.5 bars of pressure should be available at the outlet. If
the pressure droop along the supply tube is substantial, the internal pressure may
drop below 5 bars, then the MAS unit stops to regulate and gives a warning.
Consequently, we recommend a primary (inlet) pressure of min. 6 bar, preferably
7-8 bar (max. 10 bar) and a low loss gas line (8mm inner diameter, distance ≤5
meters) between the instrument and the gas supply, to assure trouble free operation even under conditions of high gas throughput. The maximum throughput depends on the experimental conditions and the probe type.
26 (327) BRUKER BIOSPIN User Manual Version 002
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MAS Tubing Connections
The following gas requirements exist:
1. At room temperature or higher: dew point min. -30 °C, compressed air will do.
2. At temperatures 200 °C or higher (suitable probe required!): nitrogen is re-
quired to prevent coil oxidation.
3. At temperatures between room temperature and -50 °C (using a B-CUX cryo
cooler with -80 °C exchanger temperature): nitrogen or compressed air with a
dew point ≤ -100 °C.
4. At temperatures below -50 °C (using liquid nitrogen and heat exchanger): boil-
off nitrogen with a dew point -196 °C.
Any compressed gas used in NMR probes must be free of any liquid droplets or of
oil (from compressor lubrication). Especially oil (even smallest amounts) will lead
to probe arcing, and/or spinning problems and potentially expensive repair. Using
boil-off nitrogen should be carefully considered, since it is by far the most reliable,
stable and trouble free source of compressed gas, to be used at any temperature!
Connections 3.5.1
MAS tubing connections are quite different between different types of probes (for
stationary, non spinning probes, only frame flush and VT gas are required:
1. WB probes, VTN, WVT and DVT probes (VTN: VT-normal range, WVT: VT-
wide range). These probes have a diameter of 72 mm and are longer than SB
probes. Probe lengths are the same up to 400 MHz, the same for 500 and 600
MHz, and longer for higher fields.
2. SB probes, VTN and DVT type probes, also major differences between older
and more modern probes. Furthermore, probes with sample insert/eject and
probes without insert/eject exist.
The major difference between DVT and VTN/WVT probes is that for VTN/WVT
probes the bearing gas is used for temperature control, whereas for DVT probes,
bearing, drive and VT gas are separate.
User Manual Version 002 BRUKER BIOSPIN 27 (327)
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General Hardware Setup
1. VT gas only input into dewar
2. Two thermocouple connectors
3. Drive gas in
4. Bearing gas in
1. VT plus bearing gas
2. One thermocouple connector at stator inlet
3. Drive gas
Wide Bore (WB) Magnet Probes
Figure 3.15. WB DVT Probe MAS Tubing Connections
Figure 3.16. VTN Probe MAS Tubing Connections Note: WVT Probes are VTN-
Type Probes
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MAS Tubing Connections
1. Sample insert/eject
2. Eject gas in
3. Insert gas in
4. Flush gas for transfer tube
5. T-piece to insert tube (allows the flush gas to be fed in
at low temperature to avoid ice formation on spinner cap)
6. Shim stack flush connection
1. Thermocouple(s)
2. Bearing gas in
3. Drive gas in
4. PICS cable
5. Heater
6. Heater cable in
7. VT gas in
8. Spin rate cable
9. Flush gas in
Figure 3.17. WB Probes: Eject/Insert Connections
Figure 3.18. WB Probes: DVT, Probe Connections for RT and HT Measurements
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General Hardware Setup
1. Frame flush for VT.
2. Ball joint takes bearing gas from the Quickfit connector at the front into the heater dewar.
3. Bearing connector for ambient temperature gas.
1
3
2
1
Standard Bore (SB) Magnet Probes
Figure 3.19. SB VTN Probe MAS Connections
With the standard bore VTN probe, quick fit connectors include:
• Bearing (3).
• Eject (2).
• Drive (5).
• Vertical (7) to the tilt stator for eject.
• Magic Angle (8) to tilt stator into the magic angle.
• Bearing sense (to supervise bearing pressure, shut down in case of a pressure
loss).
For LT experiments, the ball joint at the heater dewar must be opened and the
transfer line of the heat exchanger or the cooling unit must be connected.
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Additional Connections for VT Operation
Figure 3.20. SB DVT probe MAS connections.
The numbered connectors are the same as the VTN probe. Connectors 7 and 8
are not present since the probe does not tilt the stator for eject (not required for
2.5 mm probes).
Additional Connections for VT Operation 3.6
If Variable Temperature experiments must be run, there are a few connections to
be done which are not required for room temperature experiments.
First of all, there must be a flow of VT control gas. For MAS probes, this flow can
be the bearing gas (VTN) or it can be separate (DVT). In any case, the VT control
gas will flow through a dewar which contains a heater. There will be at least one
thermocouple which senses the temperature as close as possible to the sample.
Several requirements must be fulfilled to obtain precise and stable temperature
readings as close as possible to the real sample temperature. This will however
be part of a different chapter.
Some connections are required to control the temperature of the probe/sample,
others are necessary to protect the probe and the magnet from illegal temperatures. MAS probes are usually not as well insulated as for instance a wideline or
PE stationary probe is. Therefore the probe outer shell warms/cools down during
the experiment. The heat transfer between heater and probe electronics/probe
environment must be kept at a safe level.
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General Hardware Setup
1. Probe heater connector
2. VT gas in
3. TC connector (s)
4. Frame flush gas
Safety precautions involve flushing the probe frame, this serves to keep the
tuning elements at decent temperatures. Furthermore, the magnet must be
kept at legal temperatures to prevent freezing of O-rings or excessive expansion of the inner bore tube. The shim stack must be kept at temperatures below 70 °C, else the shim coils might be damaged. With MAS p r obes,
it must be made sure that no wet air is sucked into the eject tube, which
would lead to formation of ice on low temperature runs. This requires to
maintain some overpressure above the spinner (usually by applying some
flow to the insert gas line).
Heat exchangers must be dried with a flow of dry gas before use, so there is no
water left in which will ice up the exchanger loop. After use, they must be warmed
up and dried with a dry gas flow so that there is no water in leading to corrosion.
The following figures show the various connections to different probes.
Figure 3.21. WB Probe MAS VTN and WVT, and DVT Probe Connections
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Additional Connections for VT Operation
1. Probe heater connector
2. VT gas in
3. TC connector (s)
4. Frame flush gas
1
3
2
4
Figure 3.22. WB Probe MAS DVT Connections
In the figure above the upper thermocouple connector (read), located at stator
out, lower thermocoupler connector (regul), located at stator inlet are connected.
The VT unit must have the auxiliary sensor module to read more than one temperature. Only the TC labelled "regul" is used for regulation.
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General Hardware Setup
1. Probe heater connector
2. VT gas in
3. TC connector (s)
4. Frame flush gas
Figure 3.23. SB Probe MAS VTN
Figure 3.24. SB Probe MAS DVT Connections
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Additional Connections for VT Operation
1. Bell shaped glass dewar around sample chamber
2. Insulating and sealing Al
2O3
- felt ring
3. Cover for coil/sample compartment, fixed with plastic or metal screws
Figure 3.25. WB Wideline or PE Probes
Figure 3.26. WB Wideline or PE Probe Connections
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General Hardware Setup
Figure 3.27. Low Temperature Heat Exchanger for VTN Probes (old style)
In the figure above is a low temperature heat exchanger for VTN probes (old
style):
• 1 turn exchanger loop for SB probes;
• 2 turn loop for WB probes;
• 4 turn loop for DVT probes.
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Additional Connections for VT Operation
Figure 3.28. Low Temperature Heat Exchanger for DVT Probes
The low temperature heat exchanger for DVT probes in the figure above uses the
exchanger coil with 6 turns, the larger one may be used for high resolution
probes. To use the spring loaded connection device shown in the close-up:
1. Compress the spring.
2. Move the hollow part over the ball joint.
3. Release the spring.
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General Hardware Setup
1. Nitrogen exhaust/refill
2. Transfer line to probe (DVT)
3. VT Gas flow from B-VT 3000
4. N2 level control (to B-VT 3000 temperature controller)
1
2
3
4
Figure 3.29. Low Temperature Liquid N2 Dewar with DVT Probe/Heat Exchanger
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Additional Connections for VT Operation
1. Gas in
2. Frame flush
3. Shims
4. Spin rate
5. Heater
6. Magnet bore
7. Transfer line
8. Read and regulation thermocouples
9. Support for transfer line
1
2
3
5
6
7
8
9
4
Figure 3.30. Bottom view of Low Temperature DVT Probe/Heat Exchanger
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General Hardware Setup
1. B-CU X heat exchanger and transfer line
2. Bypass
3. Heater
4. Read and regulation thermocouples
5. PICS probe identification
6. Bearing, drive
1
2
3
5
6
4
Figure 3.31. Low Temperature Setup with B-CU X (or B-CU 05)
In the figure above is the low temperature setup with a B-CU X (or B-CU 05) for
DVT probes only, shown from the probe/magnet side.
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Probe Setup, Operations, Probe Modifiers
1. To bypass (when heater is off)
2. VT gas in, from B-VT 3000
3. Control, to B-VT 3000
4. Heater in/out (unused)
1
2
3
4
Figure 3.32. Low temperature setup with B-CU X
Probe Setup, Operations, Probe Modifiers 3.7
Setting the Frequency Range of a Wideline (single frequency) Probe 3.7.1
In a single frequency design, there are more degrees of freedom in tuning the circuit. The frequency range is set by a suitable NMR coil (see Figure 3.26.
tuning is done by a variable capacitance (1) and a fixed capacitance inside an exchangeable tuning insert (3). The purpose of this setup is to adapt the probe to
the desired task as much as possible. A wideline probe has to cope with a large
range of frequencies and line widths, and must provide the shortest possible pulses and highest possible sensitivity at the shortest possible dead time. These requirements cannot be met with one standard setup. Principles of setting up such a
probe are:
1. Select an NMR coil (2) with highest inductance that can still be tuned to the re-
quired frequency. Choose the smallest coil diameter permitted by your sample,
reduce the sample diameter if appropriate
2. Select the symmetrization insert such that the desired frequency is close to the
upper end of the available tuning range
). Fine
User Manual Version 002 BRUKER BIOSPIN 41 (327)
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General Hardware Setup
1. Tuning capacitance
2. Exchangeable NMR coil
3. Exchangeable symmetrization and Q-reduction
1
2
3
3. Select the Q value of the insert according to the expected line widths (higher Q
for line widths up to 100 kHz). Please note that multiturn coils, especially multifilament coils, have an intrinsically low Q.
Figure 3.33. RF Setup of a Wideline Single Frequency Probe
Shifting the Probe Tuning Range 3.7.2
Most probes cover a fairly wide frequency range. Changing the frequency range
of a probe requires either a change in the inductance or capacitance of the circuit.
The inductance of a circuit is hard to change unless a coil is mechanically lengthened or shortened. Most probes are tuned over a certain range by variation of a
capacitance. The frequency range is then determined by the minimum and maximum capacitance that can be set. In order to make the inductance as high as possible (since the signal from the oscillating magnetization is detected in the
inductive part), one usually chooses a capacitance with very small minimum capacitance, which again means a not large enough maximum capacitance. So in
most probes additional tuning components must be inserted (removed) to achieve
the full tuning range. The highest signal to noise is always reached with maximum
inductance and minimum capacitance, i.e. at the high end of the tuning frequency
achieved with maximum inductance.
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Probe Setup, Operations, Probe Modifiers
In a wideline probe the NMR coil is easily replaced. So with a few coils of different
inductance one can extend the tuning range determined by the tuning capacitor
inside the probe. This cannot easily be done in a MAS probe for two reasons:
1. The coil must be carefully aligned such that it does not touch the spinning rotor
2. There are two frequency ranges to be set- the X-tuning range and the proton
tuning frequency.
In such a probe, changing the coil would throw off the proton tuning totally, so a
coil change is not possible.
Extending the tuning range of a CP/MAS probe can be done in the following ways
(Figure 3.34.
1. Switch the proton transmission line between λ/4 (low range) and λ/2 mode
(high range). The proton transmission line is also part of the X-circuit and is
higher (lower) in capacitance in λ/4 (λ/2) mode (only 400 MHz and up).
2. Add a parallel capacitance to the X-tuning capacitance, which makes the ca-
pacitance bigger (tunes to lower frequency). This is normally done to shift the
tuning range to or below
3. Add a capacitance in series to another capacitance. This reduces the total ca-
pacitance and shifts to higher frequency. A capacitance in series to the λ/4 line
will reduce its total capacitance and shift the X tuning to higher frequency.
):
15
N.
4. Add a parallel coil to the NMR coil. This reduces the total inductance and shifts
to higher frequency, however at the cost of filling factor. The bigger the parallel
inductance, the smaller the high frequency shift and the loss.
User Manual Version 002 BRUKER BIOSPIN 43 (327)
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General Hardware Setup
1. X-frequency in
2. X-tuning
3. NMR Coil
4. lambda/4 switch
5. Parallel capacitance
6. Parallel inductance
7. Serial capacitance
8. H-tuning
1
2
3
5
6
7
8
4
Figure 3.34. Possible Modifiers for Probe Tuning Ranges (400 MHz and up only)
Figure 3.34.
ly. In 300 MHz and lower probes only a λ/4 line can be used, because a λ/2 would
be too long, but here λ/4 can be tuned over the full range.
All these modifications may be available for WB probes. In SB probes, they are
usually built in (if necessary) and operated by a switch.
illustrates modifiers for probe tuning ranges for 400 MHz and up on-
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Probe Setup, Operations, Probe Modifiers
1. λ-line inner conductor
2. Rotating switch at λ/4 position
3. Switch closed rotating counterclockwise (seen from probe lower end). Contact springs
(grounded) touch the λ-line at the λ/4 position
4. Switch open rotating clockwise.
5. Switch operating rod
6. Tuning capacitor at the end of the λ-line inner conductor: Fine tunes the effective length and there-
fore resonating frequency of the λ-line. This tunes the proton channel frequency (“tune”).
Figure 3.35. λ/4 (low range) and λ/2 Mode (high range), 400 MHz Probe
At 400 MHz, the wavelength is large, so the λ/4 point is below the closed section
(7) of the λ-line. At higher frequencies, the λ/4 point may fall within the closed section 7.
The proton channel (decoupling channel) is usually tuned via a so-called λ-line
(“transmission line”). This is just a coaxial cable or a coaxial conductor with an arrangement of an outer conductor (a tube) and an inner conductor (a rod). The relative diameters and distances and also the dielectric in between (usually air in WB
probes) determine the impedance of the transmission line. Since such a line is as
well an inductance as a capacitance, it is a resonating circuit. If the length of the
transmission line equals λ/4 or λ/2 of the RF-wave, it is a λ/4 or λ/2 line. Since the
upper end of the transmission line (inner conductor) is connected to the coil, high
voltage is required there. This means that the λ/4 point has low voltage but high
User Manual Version 002 BRUKER BIOSPIN 45 (327)
current, whereas the λ/2 point is at high voltage and low current. A short between
Page 46
General Hardware Setup
inner and outer conductor at the λ/4 position enforces a low voltage/high current
and fixes a certain resonance frequency.Some probes are tuned for the proton
resonance frequency by a tunable capacitor at the end of the λ/2-line (400 MHz
and up) which changes the effective length of the λ/2-line. Some probes (400 MHz
and below) are tuned by shifting the position of the λ/4 short to a higher (higher
frequency, shorter length) or lower (lower frequency, longer length) position.
Figure 3.36. A λ/4 only probe (left) and a λ/4 - λ/2 probe (right)
On the left side of the figure above is a λ/4 only probe (200, 300 MHz, 400 low
range only probes). The transmission line is only λ/4, proton tuning is done by
moving the brass block to ground (1). Proton matching is done with capacitor 2.
On the right side of the figure above is a λ/4 - λ/2 probe 600 MHz. Due to the high
proton frequency the λ/4-length shortens, the λ/4 point (1) moves inside the transmission line outer conductor (2). The screw (3) is used to set λ/4 (screw in) and λ/
2 –mode (screw out). (4) proton tuning capacitor.
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Probe Setup, Operations, Probe Modifiers
1. X-tuning variable capacitance
2. Y-tuning capacitance
3. Proton reject filter
4. Low range extension with parallel capacitance
5. Frame flush air outlet (to protect sensitive capacitors)
Figure 3.37. Without/with Parallel Capacitance to Shift the Tuning Range to Lower
Frequency
Adding a parallel capacitance does not decrease the efficiency of a circuit. However, a certain circuit has the highest possible efficiency if it is tuned with maximum inductance and minimum capacitance. Maximum inductance can usually not
be achieved due to spacial restrictions in the stator (MAS probes) or due to losses
in Q if the coil becomes too large (increase in resistance). Furthermore, capacitances are tunable, inductances usually are not, so a wide tuning range can only
be achieved via exchangeable inductances and/or capacitance with a wide tuning
range. Capacitances may look different than the one shown in the picture. Frequently, two larger capacitances are used in series to form a smaller capacitance
withstanding higher voltage. A parallel capacitance lowers and narrows the tuning
range.
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General Hardware Setup
1. X-Tuning cap
2. Parallel coil
3. Proton reject filter („trap“)
4. Probe ground
Figure 3.38. Parallel Coil to Shift the Tuning Range to Higher Frequency
This additional coil is electrically connected in parallel to the detection coil. Since it
is connected behind the proton trap, the proton channel is not influenced, but as
well the X and Y channel will be affected, because only part of the inductance is
now filled with sample. A parallel coil therefore reduces the RF efficiency quite
substantially. The losses increase as the inductance (size and number of turns) of
the parallel coil decreases. A coil of the same inductance as the detection coil will
cost 50% in S/N and pulse voltage. Usually, these coils introduce about 30% loss.
Adding a Frequency Channel to a Probe (WB probes only) 3.7.3
Probes are produced as single channel, double (channel), triple or quadruple
probes (1, 2, or 3 RF connectors on the probe). It is not possible to modify a probe
produced as a double channel probe into a triple probe, but a triple probe may be
used as triple or double probe. As multiple tuning will reduce the RF performance
of a probe on the other channels (if they are part of the same RF network), it is
better to remove an unused RF channel, if this is possible.
The usual case is triple probes or quadruple probes. A triple probe can be tuned
1
to
H, X and Y (where X is the higher frequency, Y is the lower frequency, both in
the X-nuclei range). A triple probe X/F/H only has 2 RF connectors, because 1H
and 19F are tuned to the same RF connector simultaneously. Likewise, a quadruple probe is an X/Y/F/H probe, with the X channel tuned to X and Y, and the pro-
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Probe Setup, Operations, Probe Modifiers
1. X-Tuning capacitor
2. Y-Tuning capacitor
3. X-Y trap (stops X-frequency into
Y-channel, but not Y into X-channel)
ton channel tuned to
Figure 3.9.
, Figure 3.10., Figure 3.11., Figure 3.12. for the connection of such
19
F and 1H, so there are only 3 RF connectors. Check
probes.
So the double tuning of the X channel into an X and a Y channel is an optional operation available for WB probes. SB probes are always fixed multi channel
probes, with no option to insert/remove an RF channel.
Such probes have 2 complete X-tuning circuits, almost identical in construction.
Activating the second channel means: Insert a filter which is tuned to reject at the
exact X-frequency (exactly to
nel frequency is fixed to the specified frequency (in this case,
quency has a broader tuning range (in this case
13
C frequency for a 13C/15N-2H probe). The X chan-
15N-2
13
C), while the Y fre-
H). With different filterinserts, that same probe can be modified to different frequency combinations, with
the following restrictions:
1. A frequency outside the tuning range of the probe in double mode cannot be
reached in triple mode (for instance, if the probe in double mode does not tune
31
to
P, a triple insert for 31P-13C cannot be provided (without a frequency range
shift shown in Figure 3.34.
). As the triple tuning insert will act as a load to the
whole circuit, the frequency range will shift a bit to lower frequencies.
2. Both frequencies (X and Y) should be within the same basic probe tuning
range high or low (λ/2 (high range) or (λ/4 (low range)) mode.
Figure 3.39. Mounting a Triple Insert Into a Triple Probe
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General Hardware Setup
These inserts can be made to optimize the X or the Y channel. They should be
mounted in exactly the position as indicated on the information sheet included
with the probe.
Reversing the trap may mess up tuning! Observe probe manual instructions! For
low range (below
13
C) nuclei, the probe must be in λ/4 mode. Combinations of
low/high range nuclei are difficult/impossible and always lossy!
Mounting the Probe in the Magnet/Shim Stack 3.8
Usually, the service engineer installing the magnet and the rack has considered
the local restrictions, and placed the system such that all operations which may be
required for the proper probe installation are conveniently possible. This refers to
the ease of access of the magnet bore from below and above, to mount the probe
and the sample insert devices, and also to the possibility to place VT equipment
(liquid N
without restricting standard operations.
Depending on the type of probe, VT control gas enters the probe from the side or
from behind. So it must be possible to attach the heat exchanger transfer line from
the appropriate side. Furthermore, the weight of the transfer line must be relieved
from the probe dewar ball joint, so there should be appropriate fixation points for
the transfer line. It is important that the transfer line enters the ball joint as straight
as possible, as a ball joint will cut off the flow when strongly tilted to an angle.
It should also be possible to reach the probe tuning elements (since they need to
be operated frequently) as easily as possible from the operators chair. Also, when
tuning the probe, the video screen and the preamplifier display should be easily
visible.
dewar, B-CU 05 or B-CU X) in a convenient location that allows access
2
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EDASP Display: Software Controlled Routing
Figure 3.40. Example of a 600 WB NMR Instrument Site
The example of a 600 WB NMR instrument site in the figure above provides easy
access to the probe from either side.
EDASP Display: Software Controlled Routing 3.9
The menu edasp shows all relevant RF routing and allows the routing which are
under software control to be changed. The following restrictions apply:
• Connections between transmitter and preamplifier cannot be changed (the
command edasp setpreamp with NMR Super user permissions does that).
• Channel F1 is the detection channel by default (which is no limitation).
• Detection must usually be routed via the same SGU as the F1 pulses are,
since that SGU will supply the phase coherent reference signal. In some cases, pulsing and detection may use different SGU’s, but provisions must be
made to add the signal up coherently (using exactly the same frequency on
both channels is usually coherent).
• Routing between SGU's and transmitters can only be selected if cf (the config-
uration routine) has found a hardware connection that supports this routing.
• Most routine applications will route correctly if the “default” button is pressed in
the short menu version (receiver routing not shown).
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General Hardware Setup
• If an illegal or potentially dangerous routing is selected, an error message or a
warning will pop up. Error messages will not allow selection of this routing.
• On AVIII instruments (with SGU/2), one SGU can produce two pulse trains
(within the same NCO-frequency-setting range, 5 MHz).
Figure 3.41. Short Display, Pulse Routing Only for C/N/H DCP or REDOR Experi-
ment, observing
52 (327) BRUKER BIOSPIN User Manual Version 002
13
C (above) and 15N (below)
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EDASP Display: Software Controlled Routing
In the figures above is a “short” display, pulse routing only, for a C/N/H DCP or
REDOR experiment, observing C and observing N (without any hardware
change!). Green dots indicate CORTAB linearization.
mitter since
13
C requires less power than 15N.
13
C routed via 500W trans-
Figure 3.42. Long Display, Pulse and Receiver Routing
The figure above is a “long” display, with pulse and receiver routing:
• Green dots: CORTAB done for this path, transmitter linearized.
• Dotted green lines: Possible (hardwired) routing are shown (“show RF rout-
ing”).
• Receiver routing: SGU3 used for transmit and receive (“show receiver rout-
ing”).
• Power indication: Maximum possible power output (as measured, “show pow-
er at probe in”).
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General Hardware Setup
Figure 3.43. Pulse on F2, Observe on F1 - Routing
In the figure above the SGU2 is used for pulsing and the SGU1 is used to receive.
Figure 3.44. The edasp Display for a System with two Receiver Channels
In the figure above the edasp display for a system with two receiver channels, set
for observe on
for pulse and detection on both receiver channels.
54 (327) BRUKER BIOSPIN User Manual Version 002
13
C and 15N, while decoupling on protons. The same SGU is used
Page 55
Basic Setup Procedures 4
This chapter contains information and examples on how to set up basic solid-state
NMR (SSNMR) experiments. We‘ll begin with the settings for the RF-routing of
the spectrometer, some basic setup procedures for MAS probes and how to mea
sure their (radio frequency) RF-efficiency and RF-performance. Accurate measurement of the pulse lengths and the associated RF-power levels is essential for
solid-state NMR experiments. In SSNMR, RF-field amplitudes are often ex
pressed as spin nutation frequencies instead of 90° pulse widths. Spin nutation
frequency n
pulse duration 4t
Setting up the magic angle, shimming a CPMAS probe, setting up cross polarization and measuring probe sensitivity for 13C will also be explained. This is part of
probe setup and performance assessment during installation. However, regularly
scheduled performance measurements should be part of the hardware, probes
and spectrometer maintenance.
riodically.
and 90° pulse width are related through the reciprocal of the 360°
rf
nrf = 1/(4t
such that:
p90
)= RF-field in Hz (with t
p90
Therefore, these checks should be performed pe-
p90
in µsec)
4
-
-
The checks also need to be performed if an essential piece of hardware has been
exchanged. In the following, we describe all steps which are necessary to assess
performance of a CPMAS probe, along with all necessary settings. Detailed infor
mation about TopSpin software commands is available in the help section within
the appropriate chapter.
Setting up a CPMAS probe from scratch requires the following steps:
1. Mount the probe in the magnet and connect the RF connectors of the probe to
the appropriate preamps.
2. Connect the spinning gas connectors and the spin rate monitor cable.
3. Insert a spinner with finely ground KBr and spin at 5 kHz.
It is assumed that these operations are known. If not, please refer to the following
sources:
• Probe manual.
• MAS-II pneumatic unit manual in TopSpin/help.
• SBMAS manual in TopSpin/help.
-
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Basic Setup Procedures
This chapter will include:
"Setting the Magic Angle on KBr"
"Calibrating 1H Pulses on Adamantane"
"Calibrating 13C Pulses on Adamantane and Shimming the Probe"
"Calibrating Chemical Shifts on Adamantane"
"Setting Up for Cross Polarization on Adamantane"
"Cross Polarization Setup and Optimization for a Real Solid: Glycine"
"Some Practical Hints for CPMAS Spectroscopy"
"Literature"
General Remarks 4.1
Despite the fact that most spectra taken on a CP/MAS probe look like liquids
spectra, the conditions under which they are taken must account for the presence
of strong interactions. This basically means that:
• Fast spinning, and
• high power pulses are applied.
Fast spinning requires a high precision mechanical system to allow spinning near
the speed of sound. This requires careful operation of the spinning devices.
Please read the probe manual carefully!
High power decoupling in solids requires 20-fold RF fields compared to liquids
spectroscopy, since we are dealing with >20 kHz dipolar couplings rather than
maximum 200 Hz J-couplings! This means that RF voltages near the break
through limit must be applied, and that currents of far more than 20 A occur.
It is therefore essential that:
-
• Power levels for pulses must be carefully considered before they are applied.
Always start at very moderate power levels with an unknown probe, find the
associated RF field or pulse length and then work your way towards specified
values. The same applies for pulse lengths, especially decoupling periods,
since the power dissipation inside the probe is proportional to pulse power and
duration. Always observe the limits for duty cycle and maximum pulse power.
Please refer to the probe specifications for more information. Never set acqui
sition times longer than required!
-
• Spinners and turbine must be kept extremely clean. Any dirt, especially oil,
sweat from fingers, water will decrease the breakthrough voltage dramatically.
Make sure the spinner is always clean (wipe before inserting, touch the drive
cap only) and the spinning gas supply is carefully checked to provide oil-free
and dry (dew point below 0 °C) spinning gas. Compressors and dryers must be
checked and maintained on a regular basis. Any dirt inside the turbine will
eventually cause expensive repairs.
The following setup steps need only be executed upon installation or after a probe
repair. The test spectrum on glycine should be repeated in regular intervals to as
sure probe performance.
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Basic Setup Procedures
Setting the Magic Angle on KBr 4.2
For all following steps, generate new data sets with appropriate names using the
edc command to record all individual setup steps.
RF-Routing 4.2.1
The spectrometer usually has 2 or more RF generation units (SGU's), transmitters
and preamplifiers. In order to connect the appropriate SGU to the appropriate
transmitter and the transmitter to the associated preamp where the probe chan
nels are connected, there are several routing possibilities. In order to minimise errors in hardware connections, the routing is under software control where
possible. Where cable connections need to be done manually, the software does
not allow a change. These connections are made during instrument installation.
Enter the “edasp” command (or click the Edit button in the nucleus section in the
acquisition parameter window eda) in order to get the spectrometer router display.
Alternatively, click on the routing icon in eda.
-
Figure 4.1. Routing for a Simple One Channel Experiment
The figure above shows the routing for a simple one channel NMR experiment using the 1000 W output from the high power amplifier.
In this menu, 4 RF channels are available. These 4 RF channels can be set up for
4 different frequencies. The two left most columns labelled frequency and logical
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Basic Setup Procedures
channel define the precise irradiation frequency by setting the nucleus and the offset O1 from the basic frequency. In this example, we want to set up for pulsing/observe on the nucleus 79Br. Selecting 79Br for channel F1 defines the basic
frequency BF1 of
the adjustable offset (9000 Hz in this case). Both values are added to show the
actual frequency setting, SFO1. The frequency setting is taken from a nucleus ta
ble which is calculated for the respective magnetic field B0. The index 1 in O1,
BF1, and SFO1 refers to the RF channel 1 (which is also found in the pulse pro
gram where the pulse is defined as p1:f1. Note that this index does not exist for
the following columns which represent the hardware components (SGU1-4 refers
to the slot position in the AQS-rack). The lines connecting the (software) channel
F1 to the actual frequency generation and amplification hardware can be drawn
ad libitum as long as the required hardware connections are present. The connec
tions between transmitter and preamp cannot be routed arbitrarily, because every
transmitter output is hardwired to a preamplifier, so the lines are drawn in green.
Please note that the nucleus in channel F1 is always the observe nucleus.
To set up f o r 79Br observation, click on Default and the correct routing will be
shown.
The green dot between SGU1 and amplifier 1 indicates that for this nucleus in this
connection, the transmitter has been calibrated for amplitude and phase linearity
(CORTAB).
79
Br (in this case on a 600 MHz spectrometer, 150.360709) and
-
-
-
For example, if you select a nucleus where this has not been calibrated and the
green dot is not visible, the same power level setting in dB will produce >6 dB
more power (> 4-fold power) which may destroy your probe. Calibrate power lev
els in such a case starting with 10 dB less power (higher pl(n)-value) to prevent
destruction of your probe!
The connections between SGU(n) and transmitter (n) can be altered by clicking
on either side of the connecting line (removes the connection), and clicking again
on both units you want to connect (route). In case of high power transmitters, you
have two power stages which you select by clicking on the desired stage. High
power stages require the parameter powmod to be set to “high”. Selecting a path
which is not fully routed will generate an error message.
To leave the display, click on Save. Make sure your probe X-channel is connected
to the selected preamplifier (the sequence of preamplifiers in edasp represents
the physical position of the preamplifier in the stack). If the preamp is a high power
type, make sure the correct matching box is inserted into the preamp (for 500-800
MHz systems, it would be labelled for the frequency range 120-205 MHz). Con
nections are shown in the figure below:
-
-
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Basic Setup Procedures
1: X Low Pass Filter 5: 13C Matching Box
2: Proton Bandpass Filter 6: X Probe Connector
3: X-BB Preamplifier 7: 1H Probe Connector
4: 1H HP Preamplifier
1
2
6
7
5
4
3
Figure 4.2. Probe Connections to the Preamplifier
The figure above shows the probe connections to the preamplifier with appropriate filters, placed on a table for better illustration.
Setting Acquisition Parameters 4.2.2
Create a new data set for the experiment by typing edc in the command line.
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Figure 4.3. Pop-up Window for a New Experiment
Spin the KBr sample moderately (~5, 2.5 mm: 10 kHz). In order to set up the experiment, type ased in the command line to open the table with parameters used
for this experiment.
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Figure 4.4. ased Table with Acquisition Parameters for the KBr Experiment
Then check rf routing by clicking on the Edit button in figure 4 or by typing edasp
in the command line and check powmod by clicking the default button (as de
scribed above). The rf routing for this experiment is shown in figure 1. Next set p1
= 2 µs, ns = 8 or 16. The power level at which p1 is executed is pl1. Having high
power transmitters it is important to be aware of the pulse power that is applied.
With TopSpin 2.0 and later, ased shows pl1 and pl1w, if the transmitter has been
linearized (green dot in edasp) and the transmitter power has been measured.
Set the power to about 100W.
For a non linearized transmitter, pl1 should be set to 10 in case of a 1000W transmitter and to 4 (5) for a 300W or 500W transmitter. You can also check durations
and power levels in a graphical display by clicking the experiment button in the
Pulprog window as it is shown in the figure below.
-
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Basic Setup Procedures
Figure 4.5. Graphical Pulse Program Display
In the figure above, the experiment button for opening the graphical display is
marked with a red circle.
Then match and tune the probe for this sample using the command wobb. This
will start a frequency sweep over the range of SFO1+/-WBSW/2. The swept fre
quency will only be absorbed by the probe at the frequency to which it is tuned.
-
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Figure 4.6. Display Example of a Well-tuned Probe
At frequencies, where the probe is not matched to 50 Ohms, the curve will lift off
the zero line. If tuned to a frequency within SFO1+/-WBSW/2, but ≠ SFO1, the
probe response will be off center.
N.B.: Fake resonances may appear which do not shift with probe tuning. It is always a good idea to keep track which nucleus was tuned last so it is clear what direction to tune to. Usually, turning the tuning knob counter clockwise (looking from
below) will shift to higher tuning frequency.
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Figure 4.7. Display Example of an Off-Matched and Off-Tuned Probe
Figure 4.8. Display Example Where Probe is Tuned to a Different Frequency
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Basic Setup Procedures
The figure above is an example of where the probe is either tuned to a completely
different frequency outside this window or the probe is not connected to the se
lected preamp. Check edasp for correct routing, Check for correct matching box
frequency range. Increase WBSW to 50 or 100 and try to find the probe reso
nance position.
When the probe is tuned well, as shown in Figure 4.6., start an acquisition by typing zg in the command line or clicking on the black triangle (upper left side) in the
acquisition display. Do a
ft and phase correct.
Set offset O1 to the value obtained for the center peak (see Figure 4.13.) and
start “xau angle”. This will allow you to view the fourier transformed spectrum or
the FID after ns scans. The magic angle is adjusted best when the spikes on the
FID or the spinning sidebands in the Spectrum display have maximum size, like
shown in
nance and the un-shuffled FID display mode. The spinning sidebands should
have maximum intensity, the rotational echoes on the FID should extend out to at
least 8msec in the FID-display.
Figure 4.9.. This is most easily seen with the carrier exactly on reso-
Fourier transformation and a phase correction by typing
-
-
Figure 4.9. FID and Spectrum of the 79Br Signal of KBr used to Adjust the Magic
Angle
Calibrating 1H Pulses on Adamantane 4.3
Spin the KBr sample down and change to a spinner filled with adamantane. Spin
at 5-10 kHz. Generate a new data set from the KBr data set by typing new. Set
the instrument routing for
ing figure:
User Manual Version 002 BRUKER BIOSPIN 65 (327)
13
C observe and 1H decoupling, as shown in the follow-
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Basic Setup Procedures
Figure 4.10. Routing for a Double Resonance Experiment using High Power
Stage for H and X-nucleus
The figure above shows the routing for a double resonance experiment, e.g. a 13C
experiment with
mod must be set to high. To check which power mode is selected, one may click
the default button, change to powmod high in the command line if necessary.
Note: the routing is only effective if the parameter powmod = high.
To change to proton observe, click SwitchF1/F2.
1
H decoupling. For high power transmitters, the parameter pow-
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Basic Setup Procedures
Figure 4.11. Routing for a Double Resonance Experiment, Changed for Proton
Observation
In the figure above channel F2 need not be used.
The settings for F1 and F2 are interchanged. Change rg to 8-16 and d1 to 4 sec.
Set pl1w to 50W, or to 10 dB (high power proton transmitter), 7 dB (500W proton
transmitter), 5dB (300W proton transmitter) or -4 (100W transmitter), if the green
dot does not appear in the
1
H channel in edasp. Connect the probe proton chan-
nel to the proton preamp. A proton band pass filter must be inserted between preamp and probe. Tune the proton channel of the probe using the command wobb
high. This means that the highest frequency is tuned first. Stop and type wobb
again. Then adjust the tuning of the X channel to
13
C. Alternatively, you can
switch to the lower frequency channel within wobb high by clicking on the fre
quency table symbol in the wobb display or by pressing the second touch button
on the preamp cover module twice. Then acquire ns =2 scans on the protons of
adamantane.
-
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Figure 4.12. Proton Spectrum of Adamantane at Moderate Spin Speed
Set the carrier frequency O1 on top of the biggest peak using the encircled button
in TopSpin.
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Figure 4.13. Setting the Carrier on Resonance
Click on the marked red arrow to set the observe frequency, set the position of the
cursor line, and left click on the o1 button. Acquire another spectrum, ft and
phase.
Then expand the spectrum around the adamantane proton signal including the
spinning sidebands by clicking on the left margin of the region of interest and pull
ing the mouse to the right margin of the region of interest as shown in the following figure:
-
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Basic Setup Procedures
Figure 4.14. Expanding the Region of Interest
Click right mouse button in the Spectrum window. When the Save Display Region to menu pops up, select Parameters F1/2 and OK or type dpl in the com-
mand line.
Figure 4.15. Save Display Region to Menu
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Start parameter optimization by typing popt in the command line. The popt window will appear.
Figure 4.16. The popt Window
Use optimize step by step, parameter p1 to optimize parameter p1, optimum
posmax to find the highest signal intensity (90 degree pulse) for the given value of
pl1w or pl1,and varmod lin to use linear increments for optimization. The value
for group is not used for optimizing only one parameter and the number of exper
iments nexp is set automatically when clicking on the save button. Then save table by clicking on the save button and click on start optimize to start the
optimization procedure.
The parameter value obtained by the program is written into the parameter set of
the actual experiment at the end of the optimization.
In order to stop the execution of popt use the skip or stop optimization buttons.
Skip optimization will evaluate the obtained data as if popt had finished regularly
and writes the parameter into the parameter set. Stop optimization will stop with
out evaluation of the data. You can also type kill in the command line and click on
the bar with “poptau.exe” to stop optimization. This will work like stop optimiza
tion.
Popt will generate a data set, where the selected expansion part of the spectrum
is concatenated for all different parameter values (in this case, for p1). It will have
a
procno around 999. To achieve this, processing parameters are changed ap-
-
-
-
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Basic Setup Procedures
propriately. Fourier transforming a normal FID in such a window will generate an
incorrect spectrum window.
Therefore:
Never start an acquisition in such a window, first read in the procno where popt
was started using the rep n command where n is the source procno.
Figure 4.17. The popt Display after Proton p1 Optimization
The figure above shows the popt display after proton p1 optimization, the biggest
signal is obtained at 6 µsec in this case.
Once you have obtained a 90-degree pulse for a given power setting, you can calculate power levels for different rf fields using the AU program calcpowlev. Type
xau calcpowlev into the command line and follow the instructions in the popup
window.
Calculate the power level (in Watts or dB) required to achieve a 4.5 µsec proton
90 degree pulse. In this case, 6 µsec were obtained. The command calcpowlev
calculates a power level 2.5 dB higher than used above to achieve 4.5 µsec pulse
length. Set the new pl1 as calculated and check whether 2*4.5 µsec for p1 will
give a close to zero signal. This is a safe power level for all probes for pulses up to
100 msec. length.
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Calibrating 13C Pulses on Adamantane and Shimming the Probe 4.4
A high power decoupling experiment on 13C of adamantane is used to measure
13
C pulse parameters.
NOTE: For experiments where long decoupling pulses on protons are executed,
the proton preamplifier must be bypassed, i.e. the transmitter should be wired to
the probe directly (via the proton bandpass filter) without going through the pre
amp if a high power proton preamplifier is not available. For HP-HPPR modules
1H/19
F this is not absolutely necessary, but recommended. For HPLNA 1H modules it is not required to bypass. Note that when bypassing the preamp which attenuates by about 1 dB, the proton power levels should be corrected by adding 1
dB to the pl-values.
Type edasp in the command line. You should get a display like in Figure 4.11..
Click on SwitchF1/F2 to set for 13C observation with proton decoupling. Load the
pulse program hpdec. Set cpdprg2=cw. Set pl12 to the power level that yields a
4.5 µsec proton pulse. Set pl1 such that in ased the power displayed is 200W for
13
C (7mm probe), 150W (4mm probe) or 80W (2.5 mm probe). If the green dot is
not visible in edasp for the
(500W transmitter) or 7 dB (300W transmitter) for any probe. Make sure the pro
ton channel is tuned (wobb high) and the carbon channel is also tuned (wobb).
With d1 = 4s, rg = 256 swh = 100000, td = 4k, o2 set to be on resonance on the
adamantane protons as found above, accumulate 4 scans. Set the carrier fre
quency between both adamantane 13C peaks. Reduce the spectral width swh to
50 kHz, set aq =50 msec.
13
C channel, set pl1 to 12 dB (1 kW transmitter), 9 dB
-
-
-
Acquire 2-4 scans and define the plot limits (as shown in Figure 4.14.) for the
larger of the two peaks. Define the plot limits and determine the 90 degree carbon
pulse p1, using popt. Recalculate pl1 for a 4.5 µsec carbon pulse using calcpow
lev.
Pulse continuously using gs and shim the z gradient for highest FID integral.
The gradient settings can be conveniently changed in the setsh display. Figure
4.18. and Figure 4.19. show the adamantane 13C FID without shims, with z-shim
adjusted and the corresponding setsh displays.
-
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Basic Setup Procedures
Figure 4.18. Adamantane
13
C FID with 50 msec aq. setsh Display
The figure above is an Adamantane 13C FID with 50 msec aq, with setsh display
showing no shim values. N.b.: spinning removes part of the B
in homogeneities.
0
Probes which do not use susceptibility compensated coil wire can show much
shorter T
* and require much more shimming effort (only with older probes up to
2
400 MHz proton frequency).
Figure 4.19. Adamantane
13
C FID with 50 msec aq. setsh with Optimized Z-Shim
Value
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Basic Setup Procedures
For optimum shims (rarely required) set the shims x, y, z2, xy and x2-y2, as well as
xz and yz. You may need to increase the acquisition time aq to see the effect of
increasing resolution. Save the shims using the command wsh followed by a suit
able name.
Before the shims are saved, it is recommended to reset the field value in the
bsmsdisp menu to be exactly on resonance with your shift reference sample of
choice (protons of adamantane or water in D
This allows the command probefield (TopSpin version 3 and up) to set the field
according to probe shims and magnet drift (see below, and
Shift Calibration" on page 87).
Note: For long acquisition times (aq > 0.05 s) the decoupling power level pl12
must be set to +3 dB and d1 must be increased to 6s. To allow longer acquisition
times than 50 msec, the ZGoption –Dlacq must be set in ased, if the pulse pro
gram contains the include file aq_prot.incl. Make sure the –Dlacq option is not left
set for the following steps.
O or silicon rubber).
2
"Field Setting and
Calibrating Chemical Shifts on Adamantane 4.5
-
-
In TOPSPIN (as well as in the XWIN-NMR 3.5 release) the frequency list for NMR
nuclei follows the IUPAC recommendations (see: R.K. Harris, E.D. Becker, S.M.
Cabral de Menezes, R. Goodfellow and P. Granger, NMR Nomenclature. Nuclear
Spin Properties and conventions for Chemical Shifts, Pure Appl. Chem. Vol. 73,
1795-1818 (2001) for reference).
Set the 13C low field signal of adamantane to 38.48 ppm. This will set the parameter SR which is used to calculate the chemical shift axis and the peak positions in
the spectrum.
Note: All data sets generated from this data set will have the peak positions correctly calibrated, if the magnetic field B0 is not changed. However, you must make
sure that the magnetic field is always the same. It may change, if the magnet has
a slight drift, or if different shim settings are loaded. Therefore the same shim file
should be loaded and the field be set to the same value using the BSMSDISP
command. If the magnet drift is noticeable, the calibration should be redone in
suitable intervals and the field value recorded in the lab notebook.
One can also use a spinner filled with H2O to set the field position more precisely.
Do not spin the sample and make sure the cap is well fitted. Set o1p to 4.85 ppm,
set for proton observe (as described above for adamantane), and use gs for con
tinuous pulsing and FID display. Change the field value in bsmsdisp until the FID
is exactly on resonance. Then all spectra taken should be correctly referenced
with sr = 0. For more information on correct field setting and shift calibration, see
"Field Setting and Shift Calibration" on page 87.
-
For all these experiments the field sweep must be off! When the BSMS unit is
turned off and on again, the sweep will always be on. Running spectra with the
sweep on will superimpose spectra at different fields! One can set the sweep am
plitude to 0 in order to avoid such an accidental error condition.
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Setting Up for Cross Polarization on Adamantane 4.6
Cross polarization is used to enhance the signals of X-nuclei like 13C. The strong
proton polarization is transferred (cross polarized) to the X-nuclei coupled to the
protons via strong dipolar couplings. To achieve this, the protons and the X-nuclei
must nutate at the same frequency. This frequency is the RF field applied to both
nuclei at the same time (contact time). If this condition (Hartmann-Hahn-condition)
is met, the transfer of proton magnetization to carbon is optimum. Since the pro
ton signal of adamantane is resolved into spinning sidebands even at slow spin
rates, this Hartmann-Hahn condition can be set to match for every proton spinning
sideband. Using a ramp for the proton contact pulse, the Hartmann-Hahn match is
swept over these possible match conditions and becomes insensitive to miss-sets
and different spin rates.
Start from the data set used for observing 13C under proton decoupling (1.4).
Load the pulse program cp (in eda or typing pulprog cp). The pulse sequence is
depicted in the following figure:
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Figure 4.20. A cp Pulse Sequence
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The following parameters are set:
• pl12, for the initial 90 degree pulse and the decoupling during acquisition: set
for a 4.5 µsec proton 90 degree pulse (as previously determined)
• pl1, for the carbon contact pulse, set for a 4.5 µsec carbon pulse (as previous-
ly determined)
• p3, 4.5 µsec
• spnam0, set to ramp.100 to sweep the proton contact RF field from 50 to
100%
• sp0, set to pl12 -3 dB, to account for the lower average RF over the ramp.
• p15, 2-5 msec (after the value, specify m to make it milliseconds, else it is tak-
en as microseconds)
• cpdprg2, select cw
• o1, set between both adamantane peaks
• o2, set to be on resonance on adamantane protons
Acquire 2 or 4 scans, then set plot limits for both peaks, and optimise p3 (+/- 2
µsec) and pl1 (+/- 2 dB) for best signal. Fig. 21 shows a Hartmann-Hahn match
optimization over 4 dB using a ramp contact pulse going from 50 to 100% ampli
tude.
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Figure 4.21. Hartmann-Hahn Optimization Profile
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The wiggles besides the signals stem from truncation of the FID after 50 msec acquisition time.
To exemplify the existence of several HH-conditions on a spinning adamantane
samples, another HH profile (
tact pulse is used. There are several maxima corresponding to matches on the
sideband orders n+2, n+2, n+1, n+0, and n-1. The largest intensity is seen for n+/
-1, the intensities are very sensitive to the RF-level which is varied in 0.2 dB steps.
Using a ramp makes the experiment much more stable and more quantitative.
Problems may arise if the proton T
must be employed. It makes therefore sense to use a flatter ramp (70-100%) and
optimize for the spin rate which is used.
Figure 4.22.) is shown where a square proton con-
is short, since usually longer contact times
1ρ
Figure 4.22. Hartmann-Hahn Optimization Profile Using a Square Proton Contact
Pulse
The sideband order 0 at 4.8 dB gives a rather small intensity. A ramp sweeping
over 3.5-6.5 dB would cover both most efficient HH conditions. Note that increas
ing the spin rate would shift all maxima except the one at 4.8 dB further out.
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Cross Polarization Setup and Optimization for a Real Solid: Glycine 4.7
Adamantane is highly mobile even in the solid state. Therefore it behaves differently from a “hard” solid like glycine. For instance, it is not sensitive to decoupling
mis-adjustments, and also not sensitive to miss-sets of the magic angle. It is how
ever extremely sensitive to HH misadjustment. Glycine is therefore used for fine
tuning of the decoupling parameters and signal-to-noise assessment. Start with
the parameters found for adamantane, using a 50-100% ramp (ramp.100) and
p15=2 msec for contact, aq = 20 msec. Change the sample from adamantane to
glycine.
Since glycine may exist in two different crystal modifications with very different
CP-parameters, and since packing of the spinner determines crucially the achiev
able S/N value, it is useful to prepare a reference spinner with pure α-glycine, finely powdered and densely packed. α-glycine is prepared by dissolution of glycine in
distilled water and precipitation with acetone, quick filtering and careful drying in a
desiccator. Drying is important because wet glycine may readily transform, espe
cially when kept warm, into γ-glycine. α-glycine has two carbons with shifts of
176.03 and 43.5 ppm. γ-glycine shows resonances somewhat shifted to higher
field, sharper lines, longer proton T
experiment time and less signal to noise.
and shorter proton T1ρ which results in longer
1
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Spin the glycine sample at 5 kHz (7mm spinner), or 10 kHz (smaller spinners 4,
3.2 or 2.5), tune and match the probe.
The glycine cp/mas 13C-spectrum taken under the same conditions as adamantane previously will look like in Figure 4.23., far from optimum:
Figure 4.23. Display Showing α-Glycine Taken Under Adamantane Conditions, 4
scans
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The figure above shows α-glycine taken under adamantane conditions, 4 scans:
Incorrect carrier setting, α-carbon at 43 ppm insufficiently decoupled. Angle is set
correctly, because carboxyl peak at 176.03 ppm shows a narrow lorentzian line
shape. HH condition looks okay.
Now reset the carrier as shown in Figure 4.13.. o1p should be around 100 ppm,
in the middle of most carbon spectra. Acquire a spectrum, set the plot limits (Fig-
ure 4.14., Figure 4.15.) for the peak at 43 ppm, and start popt, optimizing o2 for
maximum signal (+/- 2000 Hz around the current position) in steps of 500 Hz. The
following result will be obtained:
Figure 4.24. Optimization of the Decoupler Offset o2 at Moderate Power, Using
cw Decoupling
Since the proton spectrum of glycine extends around 5 ppm, the optimum decoupler offset will be obtained at higher frequency than the adamantane proton peak
(around 1.2 ppm). Decoupling is still inefficient, since cw decoupling is used which
does not cover the whole proton shift range. Also decoupling power is too low with
a proton pulse of 4.5 µsec. Glycine requires about 90 kHz of decoupling RF, corre
sponding to a 2.7 µsec proton 90 degree pulse. This can be obtained with probes
of 4mm spinner diameter and smaller (2.5, 3.2 mm). For a 7 mm probe, 3.5
(4µsec) can be expected at proton frequencies below 500 (at 500) MHz. Use cal
cpowlev to calculate the required power level pl12 and set p3 to twice the expected proton pulse width. Check with 4 scans whether a close to zero signal is
obtained. Compared to 4.5 µsec, a 2.7 µsec pulse requires about 4.5 dB more
power (corresponding to almost 4 times more power!!!).
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With p3 properly set, a spectrum like in Figure 4.25. should be obtained, with
about 93 kHz decoupling RF field.
Figure 4.25. Glycine with cw Decoupling at 90 kHz RF Field
In the spectrum above, a lorentzian deconvolution (Analysis menu) shows a line
width of 71 Hz for the peak at 43 ppm. The line width achievable under optimum
decoupling conditions varies with the magnetic field. At fields below 9.4 Tesla
(400 MHz) this line is substantially broadened by second order quadrupolar inter
action to 14N. At fields above 9.4 Tesla (500 MHz and higher), the residual line
width is mostly determined by chemical shift dispersion and insufficient decou
pling. Here less than 60 Hz (at 600 MHz) are expected. More efficient decoupling
schemes must be applied especially at higher magnetic fields. A more efficient
decoupling scheme is spinal64. Select cpdprg2 = spinal64, set pcpd2 to proton
180 degree pulse – 0.2 µsec for a start. A glycine spectrum as shown in
4.26. is obtained.
Figure
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Table 4.1. Summary of Acquisition Parameters for Glycine S/N Test
Parameter Value Comments
PULPROG cp cp.av for AV1 and 2
NUC1 13C Nucleus on f1 channel
O1P 100 ppm
NUC2 1H Nucleus on f2 channel.
D1 4 s Recycle delay.
NS 4 Number of scans.
SWP 300 ppm Spectral width for Glycine.
TD 2048 Number of acquired complex points.
CPDPRG2 SPINAL64 Decoupling scheme f2 channel (1H).
13
C offset
SPNAM0 ramp.100 or ramp 70100.100 For ramped CP.
P15 2 ms Contact pulse (f1 and f2 channel).
PL1 Set for 4-4.5 µsec P90.
SP0 (or pl2 AV1+2) Set for 4-4.5 µsec P90 – 2 dB (optimize).
PL12 High power level f2 channel (1H) excitation
and decoupling.
P3 90
PCPD2 or
o 1
H pulse at PL12 (f2 channel).
SPINAL64 decoupling pulse.
P31 (AV1+2)
O2P 2.5 - 3 ppm
1
H offset - optimize in 400 - 500 Hz steps for
maximum signal of aliphatic peak.
Note that the spectral window (swp) is set in ppm which makes the acquisition
time dependant on the B
for the linewidths dependence on the B
-field at a given td of 2k. This is intended and accounts
0
-field. The glycine lines show a broaden-
0
ing proportional to B0 due to chemical shift dispersion. To make S/N values more
comparable, this accounts for shorter T
at higher field.
2
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Table 4.2. Processing Parameters for the Glycine S/N-Test
Parameter Value Comment
SI 2-4 k Twofold or fourfold zero filling.
WDW No No apodization used for S/N measurement In this case.
PH_mod Pk Phase correction if needed.
BC_mod Quad DC offset correction on FID.
FT_mod Fqc
Note: No line broadening is applied since the acquisition time is set appropriately.
Figure 4.26. Glycine Spectrum with Spinal64 Decoupling at 93 kHz RF field
Here, the line width of the line at 43 ppm is fitted to be about 50 Hz: Correspondingly, the intensity is much higher. The sinocal routine calculates 80:1 S/N, using
250 to -50 ppm spectrum range, 50 to 40 signal range and 10 ppm noise range.
On this triple probe, more than 100:1 is expected. What else needs to be opti
mized? Two more parameters are essential:
1. The power level at HH contact
2. The decoupling pulse pcpd2.
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The spectrum of Figure 4.26. was taken at contact power levels as set for adamantane. Furthermore, a 50% ramp was used, which has a rather low average
RF level corresponding to about 5.7µsec in this case (25% less than 4.5 µsec).
This does not spin lock the protons well enough. So the power level of the contact
needs to be increased. Set spnam0 = ramp70100.100. Set sp0 and pl1 to about
2 dB less attenuation and check S/N again. Re-optimize the HH condition observ
ing the peak at 176 ppm (which is less strongly coupled to protons and therefore
exhibits a sharper HH matching condition) in steps of 0.3 dB. In this case, S/N im
proves to 100:1. Then optimize the decoupling pulse pcpd2 in steps of 0.2 µsec,
observing the peak at 43 ppm (which is more sensitive to decoupling mis-sets).
Here, this led to another 10% improvement in S/N.
Good Laboratory Practice requires that evaluation measurements be taken in
suitable periods. Store the optimized glycine spectrum together with the following
important information:
1. Value of field setting.
2. Name of the shim file.
3. Name of the operator.
4. Probe setup (triple mode or double mode, high range or low range setting, WB
probes only, name or part number of the probe).
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5. Description of the sample (which reference rotor, weight of glycine and spinner).
6. Any additional comments, for instance the reading of the micrometer setting
for the X tuning adjustment (not available on all probes).
Write this information into the title file so it is stored with the data set as well as all
other acquisition and processing parameters. Recalling this data set and acquir
ing a new data set should give the same spectrum within +/- 10% of S/N.
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Some Practical Hints for CPMAS Spectroscopy 4.8
Some general recommendations for reasonable RF-fields used in WB probes:
Table 4.3. Reasonable RF-fields for Max. 2% Duty Cycle
Probe Nucleus
2.5mm CPMAS double resonance 35
kHz max sample rotation
2.5mm CPMAS double resonance 35
kHz max sample rotation
3.2mm CPMAS double resonance 24
kHz max sample rotation
3.2mm CPMAS double resonance 24
kHz max sample rotation
4 mm CPMAS double resonance
probe (15 kHz max. sample rotation)
4 mm CPMAS double resonance
probe (15 kHz max. sample rotation)
4 mm CPMAS triple resonance probe
(15 kHz max. sample rotation)
7mm CPMAS double resonance probe
(7 kHz sample rotation)
7mm CPMAS double resonance probe
(7 kHz sample rotation)
Decoupling power over 50 ms, 200ms,
500ms. Contact pulse up to 10 ms
1
H 115 kHz (2.2µs 90º pulse), 75 kHz, 40 kHz
71 kHz (3.5 µs) contact
13
C 83 kHz (3 µs 90º pulse)
71 kHz (3.5 µs)
1
H 110 kHz (2.3 µs), 60 kHz, 35 kHz
68 kHz (3.7 µs)
13
C 78 kHz (3.2 µs)
68 kHz (3.7 µs)
1
H 92.5 kHz (2.7us 90º), 50 kHz, 30 kHz
62 kHz (4 µs)
13
C 71 kHz (3.5 µs)
62 kHz (4 µs)
13
C 66 kHz (3.8 µs)
50 kHz (5 µs)
1
H 70 kHz (3.6 µs 90º pulse), 35 kHz, 20 kHz
50 kHz (5 µs)
13
C 55 kHz (4.5 µs)
50 kHz (5 µs)
Note: Higher RF power levels should only be applied if necessary and within
specifications. For special probes, max. allowed RF fields may be lower. Check
with your Bruker BioSpin applications support if in doubt.
In order to have quantitative information about the precision of your magic angle,
one may measure the line width of the KBr central peak and compare it with the
line width of the 5
th
spinning sideband. If the linewidths compare within ± 8% then
the MA-setting is acceptable. The line-width comparison is conveniently achieved
with the command peakw, expanding the display first around the center line, typ
ing peakw and then repeating this with the 5th sideband to either side.
Most cp/mas probes are tunable over a large range of X-frequencies. It can sometimes be fairly difficult to retune a probe to an arbitrary frequency within the tuning
range. NEVER just load a nucleus and blindly tune and match the probe, using a
small wobble width (wbsw) of 10 MHz or less. Instead, either note the current tun
ing position of the probe into the lab notebook and start retuning to the new nucleus frequency from this frequency on, following the probe response over the whole
frequency range using a large wbsw of 50 MHz. Alternately, check the microme
ter setting of the X-tuning adjustment and conclude from that to which nucleus the
probe is tuned. Make a list of micrometer settings for the most frequently mea
sured nuclei.
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Basic Setup Procedures
Remember which way to turn the tuning knob to tune to higher and lower frequencies. On most probes, turning the adjustment counter clockwise tunes to higher
frequency. Do not change the matching adjustment until you have found the cur
rent tuning position of the probe, else you may loose the probe response totally.
Do not tune without having the appropriate matching box fitted to the preamp.
Fake resonances may appear due to filters between probe and preamp, because
filters are also tuned circuits. Remove all filters before tuning over a wide range,
and fine tune again (wbsw ≤ 10 MHz) when the probe is tuned close to the de
sired frequency.
Changing the proton tuning will affect the X-tuning, so always tune the proton
channel first, then the X-channel.
Setting a probe from high range to low range mode (lambda/4 switch) will shift the
X-tuning to lower frequency by many MHz, the proton frequency will only change
by a few MHz.
An empty probe may tune as much as 10 MHz higher on the proton channel compared to a probe with a spinner in.
When a probe has not been used over an extended period, humidity may collect
inside the turbine, causing a few harmless arcs (RF-breakthrough) on the proton
channel. If the arcing does persist and/or gets worse, have the probe checked.
Usually this means that dirt has accumulated inside the turbine or on the RF-coil.
Cleaning should be done by a trained person only.
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Regular probe performance checks comprise:
• Checking the magic angle setting (KBr)
• Checking the shims (Adamantane)
• Checking S/N performance on glycine
These checks must also be performed after a probe repair. Since a repair may result in a more efficient power conversion, start with slightly reduced power settings.
SB probes flip the stator vertical for sample eject. These probes require some
more effort to assure a correct angle setting.
Remember to always approach the magic angle setting from the same side!
To check the reproducibility of the magic angle setting, take a KBr spectrum, stop
spinning, eject and reinsert the sample, take another spectrum into a new data
set, compare in dual display mode.
If the second spectrum is worse, dial less than 1/8th of a turn counterclockwise.
Take another spectrum, compare again.
A laboratory notebook should be kept with the following entries (a suitable form
for printout is supplied in the
"Appendix"):
• Name of the shim file and field value for every probe.
• Value of power level in dB and power in watt (if available) for proton decou-
pling (pl12, pl12W) and associated pulse lengths p3, pcpd2.
• Value of proton contact power level in dB and watt (sp0, sp0W).
• Value of carbon contact power level (pl1, pl1W) and associated pulse length
p1.
• S/N value obtained on glycine, SR value for shift calibration, line width on α-
carbon in Hz.
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Field Setting and Shift Calibration 4.9
Note: It is essential that, if spectra taken at different times and/or taken with different probes need to be compared, the shift calibration is executed correctly. If the
magnetic field was not the same, the spectra will have different values of Spec
trum Reference (sr).
To reduce the requirement of readjustment and to make referencing more reliable, the field should be set to be the same for all spectra.
To keep the field the same, 2 parameters must be taken into account:
1. The drift of the magnetic field
2. The difference in shims and field between different probes.
The drift of the magnet should be measured in the following way:
Insert a sample of D2O and run a proton spectrum just like it was done on adamantane in "Calibrating 1H Pulses on Adamantane" on page 65.
Without changing any parameter, rerun the spectrum every 10 minutes for a full
day. This can be done with popt, storing the data as a 2D experiment, or use the
pulse program zg in a 2D data set, with appropriate settings for d1 and td1 so that
the drift of the magnet can be followed by the changes in peak positions of the
D
O protons. The pattern of changes in the peak position will reveal whether the
2
changes are solely due to magnet drift, or whether there are additional disturbanc
es to the magnet field. A magnet drift will always be constant towards lower frequency (note.: A freshly charged magnet may also drift to higher frequency, but
this will change, so it makes no sense to account for this initial drift). A nonlinear
drift pattern indicates temperature changes, abrupt changes reveal magnetic dis
turbances (elevator, cars or trucks trains, or the keys in your pocket- only if your
magnet is not shielded).
-
-
-
From these data, filter out the linear magnet drift. Determine the number of digits
the field value in the bsmsdisp menu must be changed to set the field back to the
exact same value as in the first spectrum. Recalculate this number to a drift time
of exactly 1h/24h. Note these values as your magnet drift rate.
This drift rate will only reach a stable and constant value some time after charging, so the drift rate measurement should be repeated until the drift value is constant. This may take some weeks to months (for high field magnets).
The magnet drift value will allow to calculate the time dependant component of the
field. The probe dependant component can be established by shimming every
probe and setting the field on the same sample, following the same procedure for
every probe after shimming. When then the shim file is written, the current (cali
brated) field position is written to disk with the shim file.
Executing the AU program (or command, TopSpin version 3.0 and later) probe
field will now set the field to the appropriate value according to drift and time (tak
en from the date of the shim file, so the computer clock should be correct) and
probe shims (from the current probe setting, so the appropriate probe must be se
lected in edhead). However: this will only work if all shim files contain the precisely
determined field value for the same reference compound.
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Literature 4.10
Shift referencing:
1. R.K Harris, E.D. Becker, S.M. Cabral de Menezes, R. Goodfellow, and P. Granger, NMR Nomenclature. Nuclear Spin Properties and conventions for Chemical shifts, Pure Appl. Chem. Vol. 73, 1795-
1818 (2001)).
2. W.L. Earl, and D.L. VanderHart, Measurement of 13C Chemical Shifts in Solids, J. Magn. Res. 48, 3554 (1982).
3. C.R. Morcombe, and K.W. Zilm, J. Magn. Reson. 162 p479-486 (2003)
4. IUPAC recommendation (Harris et al.):
5. http://sunsite.informatik.rwth-aachen.de/iupac/reports/provisional/abstract01/harris_310801.html
Cross polarization:
1. D. Michel, and F. Engelke, Cross-Polarization, Relaxation Times and Spin-Diffusion in Rotating Solids,
NMR Basic Principles and Progress 32, 71-125 (1994).
2. G. Metz, X. Wu, and S.O. Smith, Ramped amplitude Cross Polarization in Magic-Angle-Spinning
NMR, J. Magn. Reson. A 110, 219-227 (1994).
3. B.H. Meier, Cross Polarization under fast magic angle spinning: thermodynamical considerations,
Chem. Phys. Lett. 188, 201-207 (1992).
4. K. Schmidt-Rohr, and H.W. Spiess, Multidimensional Solid-State NMR and Polymers, Academic Press
(1994).
5. S.Hediger, B.H. Meier, R.R. Ernst, Adiabatic passage Hartmann-Hahn cross polarization in NMR un-
der magic angle sample spinning, Chem. Phys.Lett 240, 449-456 (1995).
88 (327) BRUKER BIOSPIN User Manual Version 002
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Decoupling Techniques 5
Line shapes in solids are often broadened by dipolar couplings between the spins.
If the coupled spins are of the same kind, it is called homonuclear dipolar cou
pling. heteronuclear dipolar couplings exist between nuclei of different kind. While
most dipolar couplings between X-range nuclei can be removed by magic angle
spinning, couplings between
removed by spinning.
can be obtained by different forms of rf-irradiation with or without sample spinning.
It is possible to suppress homonuclear couplings without suppressing heteronu
clear couplings. Most frequently, the nucleus 1H must be decoupled when X-nuclei like 13C or 15N are observed, since it is abundant and broadens the line
shapes of coupled X-nuclei strongly.
Heteronuclear Decoupling 5.1
1
H, 19F and X nuclei cannot easily and efficiently be
Decoupling of homonuclear and heteronuclear interactions
5
-
-
CW Decoupling 5.1.1
CW decoupling simply means irradiating the decoupled spins (usually protons)
with RF of constant amplitude and phase. The decoupling program is called cw or
cw13 and it uses pl12 or pl13, respectively. The decoupling programs select the
power level and pl12 does not need to be specified in the pulse program, if it is
not used elsewhere. In the decoupling program there is also a statement setting
the RF carrier frequency, according to the parameter cnst21, which is zero (on re
sonance) by default. In order to optimize decoupling, one uses the highest permitted rf-field (e.g. 100 kHz for 4mm probes) and optimizes the carrier frequency o2
or o2p using popt.
The cw –decoupling program is written as follows:
0.5µ pl=pl12 ; reset power level to default decoupling power level
1 100up:0 fq=cnst21; reset decoupling carrier frequency to o2+cnst21
jump to 1 ; repeat until decoupler is switched off by do in the
; main ppg
CW decoupling suffers from the fact that protons have different chemical shifts, so
irradiating at a single frequency does not decouple all protons evenly. At higher
magnetic fields this becomes more evident, since the separation due to the mag
netic field increases. CW decoupling requires fairly high decoupling power to be
efficient.
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TPPM Decoupling 5.1.2
TPPM decoupling surpasses the traditional cw decoupling. The decoupling programs tppm15 and tppm20 use a 15 and 20 degree phase shift between the two
pulses, respectively. Both operate at power level pl12. The cpd program tppm13
uses 15 degree phase shift, as tppm15, but operates at power level pl13.
In order to optimize the decoupling one optimizes pcpd2 (AV3, or p31, AV1+2)
with popt and the carrier frequency, by varying o2 or o2p. Strongly proton cou
pled 13C-resonances narrow substantially, especially at high magnetic fields
(>300 MHz).
The figure below shows an arrayed optimization using popt for the TPPM phase
tilt and pcpd2 (available in TS2.0 and higher).
-
Figure 5.1. Optimization of TPPM Decoupling, on Glycine at Natural Abundance
The figure above shows optimization of TPPM decoupling, on glycine at natural
abundance,
13
C CPMAS at 5 kHz spin rate. Each block represents a 2° degree increment of the phase toggle and the variation in each block stems from incrementation of the pulse width in 0.2 µs increments. Optimum decoupling was found with
a 4.5 µs pulse at a 16° phase toggle. It is obvious that more than one near opti
mum combinations of phase toggle and pulse length exist.
Reference:
1. A.E. Bennett, C.M. Rienstra, M. Auger, K.V. Lakshmi, and R.G. Griffin; Heteronuclear decoupling in rotating solids, J. Chem. Phys. 103 (16); 6951 – 6958 (1995).
90 (327) BRUKER BIOSPIN User Manual Version 002
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SPINAL Decoupling 5.1.3
SPINAL provides adequate decoupling bandwidth even for high field (>400 MHz)
instruments at an RF-level of 80 kHz or higher. SPINAL-64 (64 phase permutati
ons) outperforms TPPM and may be used as standard decoupling sequence. SPINAL-64 can be optimized in the same way as TPPM, by incrementing pcpd2 (p31)
(the phase shifts are fixed). The decoupling pulse is an approximate 180° pulse.
Reference:
1. B.M. Fung, A.K. Khitrin, K. Ermolaev, J. Magn. Reson. 142, 97-101 (2000).
Swept-Frequency-TPPM 5.1.4
This decoupling method combines TPPM and a frequency variation via. pulse
length variation to achieve a wider decoupling bandwidth. The decoupling efficien
cy is better than TPPM (especially at high fields), and comparable to if not better
than SPINAL-64. The corresponding cpd-program is called swftppm.
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-
Reference:
1. R.S. Thakur, N. D. Kurur, and P. K. Madhu, J. Magn. Res. 193, 77 (2008).
XiX Decoupling 5.1.5
XiX decoupling requires high spinning speeds, but decouples at a moderate RF
level. 180° proton pulses are used, synchronized to the rotor speed such that re
coupling does not occur (pcpd2≠n/4*rotor periods). Usually, pcpd2 is selected to
be about 1/3 rotor period. The decoupler power level must be adjusted to produce
a 180° pulse of (rotor period)/3.
Reference:
1. A. Detken, E. H. Hardy, M. Ernst, and B. H. Meier, Chem. Phys. Lett. 356, 298-304 (2002).
Pi-Pulse Decoupling 5.1.6
Pi−pulse decoupling is a decoupling program, for weaker nuclear interactions like
J couplings or weak dipolar interactions, using rotor synchronized 180° pulses. π-
pulse decoupling uses the xy-16 phase cycle for large bandwidth. Abundant pro
tons cannot be sufficiently decoupled with this method, but it is very suitable to remove couplings to 31P, which is hard to do by cw or tppm, since the chemical shift
range is wide. Likewise, it can be used to decouple dilute spins or spins which are
homonuclear decoupled by spinning (
19
F).
-
-
Reference:
1. S.-F. Liu and K. Schmidt-Rohr, Macromolecules 34, 8416-8418 (2001).
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Decoupling Techniques
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Homonuclear Decoupling 5.2
Homonuclear decoupling refers to methods which decouple dipolar interactions
between like spins. Those are only prominent between abundant spins like
19
F and 31P (and potentially some others). This interaction cannot easily be spun
1
H,
out in most cases and renders NMR-parameters like chemical shifts of the homo
nuclear coupled spins or heteronuclear couplings and J-couplings to other (X-)nuclei unobservable.
Multiple Pulse NMR: Observing Chemical Shifts of Homonuclear Coupled Nuclei 5.2.1
Multiple pulse NMR methods are covered in the chapters about CRAMPS of this
manual collection. The principle of those methods (CRAMPS, if MAS is used to
average CSA interactions simultaneously), is to set the magnetization of the spins
into the magic angle, using a suitable pulse sequence. In this case, the dipolar
couplings between those spins are suppressed. Short observation windows be
tween pulses allow observation of the signal from the decoupled nuclei.
Reference:
1. S. Hafner and H.W. Spiess, Multiple-Pulse Line Narrowing under Fast Magic-Angle Spinning, J.
Magn. Reson. A 121, 160-166 (1996) and references therein.
Multiple Pulse Decoupling 5.2.2
-
-
Multiple Pulse Decoupling: Observing dipolar couplings and j-couplings to homonuclear coupled nuclei.
Homonuclear couplings between abundant spins (usually protons) superimpose
their heteronuclear dipolar couplings to X-spins and J-couplings to X-spins so
these (distinct) couplings are not observable. homonuclear decoupling protons
while observing X-spins makes these couplings observable. Any method used in
multiple pulse NMR (section
5.2.1) may be used to achieve this.
BR-24, MREV-8, BLEW-12
Used as heteronuclear decoupling methods, the window between pulses may be
shortened or omitted (semi-windowless or windowless sequences). These se
quences work well, but have rather long cycle times and are therefore not suitable
for fast spinning samples. Else they work in a similar fashion as the sequences
covered in the following. BLEW-12 decoupling is supplied as a standard cpd-pro
gram. It consists of a windowless sequence of 90° pulses with suitable phases.
High RF levels for decoupling provide better resolution.
FSLG Decoupling
The Frequency Switched Lee Goldburg (FSLG) sequence may be used at spin rates up to 15 kHz. It is a homonuclear decoupling sequence which rotates the interaction Hamiltonian around an effective field, aligned at the magic angle (arctan
) with respect to the Zeeman field in the rotating frame. The tilt is achieved by
off resonance irradiation at the Lee Goldburg frequency fLG according to the Lee
Goldburg condition.
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2π
The off-resonance condition depends on the RF-field of irradiation, not very sensi-
tively however. The irradiation frequency jumps between +/- (RF-field)/sqrt(2) for
the duration of two 360°pulses on resonance (=293° pulses at the LG-frequency)
with a 0/180° phase alternation. The include file <lgcalc.incl> calculates all values
according to the RF-field (set in Hz as cnst20) within the pulse program.
Figure 5.2. Geometry for the FSLG Condition
Note that B
erence 2). Note the sign of B
tive field. A positive B
points along the 1 1 1 direction in the 3 dimensional space (see Ref-
eff
and a B1 with phase 0 results in the effective field being in
off
when calculating the actual direction of the effec-
off
the positive quadrant along the magic angle in the X-Z plane of the rotating frame.
Two methods are available to achieve such a frequency switch experimentally.
One method is simultaneous switching of frequencies and phases. The other
method uses phase-modulation. Frequency, time and phase relate to each other
as derivative of phase and time as to get
= .../. The relationship describes the
rate at which a phase of the rf-pulse must be changed in order to achieve a certain frequency offset. Vinogradov et al. describe this approach under the acronym
PMLG (Phase Modulated Lee Goldburg).
Used in combination with cp signal generation, both methods allow observing proton-J-couplings to the observed X-nucleus. However, only samples with very narrow lines will produce well resolved J-couplings as shown below on adamantane.
Harder solids require careful adjustment and fairly high power levels to show
barely resolved couplings, since the linewidths achieved are broader than what
can be achieved with standard decoupling sequences like tppm. Since the hetero
nuclear X-H-coupling remains, there may be spinning sidebands from this coupling, in addition to CSA sidebands.
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Decoupling Techniques
Figure 5.3. FSLG Decoupling Pulse Sequence Diagram
Figure 5.4. Adamantane, FSLG-decoupled, showing the (downscaled) C-H J-
couplings.
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Ω
The figure above shows homonuclear proton decoupling on center packed adamantane sample rotating at 7 kHz, 100 kHz 1H decoupling field. Note that good
B
-homogeneity is required. Use a CRAMPS spinner (12 μl sample volume in a
1
4mm spinner).
Setting up the experiment:
1. Use center packed adamantane in a CRAMPS rotor, unlabeled and a spinning
rate of 10 kHz for adamantane.
2. Start from a data set with well adjusted HH condition on adamantane.
3. Generate a new data set with edc.
4. Readjust decoupling power pl12 and p3, pcpd2 for 70-100 kHz RF field, de-
termine the precise RF field (preferably via a 360° proton pulse p3).
5. Load the pulse program fqlg. This uses frequency shifts with simultaneous
phase shifts for FSLG-decoupling at pl13.
6. Set pl13 to achieve the same RF-field as measured in step 4, set cnst20 to
the value of RF field in Hz. The pulse program contains the include file <lg
calc.incl> which calculates the required frequency shifts to either side (shown
in ased as cnst22 and cnst23). Cnst24 provides an additional overall offset to
compensate for phase glitch. With proper probe tuning and 50
cnst24 should be close to zero.
match,
-
7. Set acquisition and processing parameters according to Table 5.1. and Table
5.2..
A spectrum like in fig. 4 should be obtained. If the splitting is worse, optimize with
pl13 and cnst24. Usually, somewhat less power than calculated is required.
The FSLG decoupling scheme is also implemented as cpd-program cwlgs. The
include file lgcalc.incl is also required. With cpdprg2 = cwlgs, the standard cp
pulse program can be used. The ZGOPTN –Dlacq (ased) should be set in order
to allow decoupling times >50 ms.
Table 5.1. Acquisition Parameters
Parameter Va lu e Comments
pulprog fqlg AV3, use fqlg.av for AV1+2.
d1 4 s Recycle delay.
ns 4-16 Number of scans.
aq 80 ms Acquisition time.
spnam0 ramp.100 or, ramp70100.100 For ramped CP.
pl12, p3 set for p3=90°
sp0, pl1 set for cp
p15 5-10m
pl13 set for 70-100 kHz Optimize for best resolution.
cnst20 70000-100000 Equals the applied RF-field.
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2
π
Table 5.1. Acquisition Parameters
cnst24 0 To be optimized.
cnst21 0 Reset proton frequency to SFO2.
Table 5.2. Processing Parameters
Parameter Value Comment
SI 2*td Adequate 4fold zero filling.
WDW no No apodization.
PH_mod pk Phase correction if needed.
BC_mod quad DC offset correction.
As mentioned above, frequency shifts can also be generated by a phase gradient
shape. A phase change of 360° per second corresponds to a frequency of 1 Hz,
as can easily be visualized. The frequency shift which needs to be achieved is
±RF-field/
corresponding to a 293° flip angle on resonance, it can easily be calculated that a
phase change over 209° during a 293° flip angle pulse is required to achieve this.
. Since the pulse duration must achieve a 2 rotation off resonance,
Figure 5.5. Shape with Phase Gradients
In the figure above: Shape with phase gradients for positive and negative offsets
and corresponding phase change, stdisp –display of lgs-1 shape. Amplitude is
100% throughout.
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References:
Decoupling Techniques
Vinogradov et. al. have published shapes with much fewer steps and different
phases. The pulse length for the shape does not depend on the number of steps,
but only on the applied RF-field. Using the include file lgcalc.incl, a pulse p5 is cal
culated from cnst20=RF-field in Hz. The total shape pulse length must be 2*p5.
To use pmlg decoupling, save the pulse program fqlg under a different filename
and change calculations and loop as follows:
define loop counter count; calculate number of LG periods according to aq
"count=aq/(2*p5)"
define pulse pmlg
"pmlg=2*p5"
"sp1=pl13" set shape power to pl13 for LG (TS2.1 only)
.
3 (pmlg:sp1 ph3): f2 for one full PMLG unit, as for lgs-1 shape
lo to 3 times count
-
1. A. Bielecki, A.C. Kolbert, and M.H. Levitt, Frequency-Switched Pulse Sequences: Homonuclear De-
coupling and Dilute Spin NMR in Solids, Chem. Phys. Lett. 155, 341-346 (1989).
2. A. Bielecki, A.C. Kolbert, H.J.M. deGroot, R.G. Griffin, and M.H. Levitt, Frequency-Switched Lee-Gold-
burg Sequences in Solids, Advances in Magnetic Resonance 14, 111-124 (1990).
3. E. Vinogradov, P.K. Madhu, and S. Vega, High-resolution proton solid-state NMR spectroscopy by
phase modulated Lee-Goldburg experiments, Chem. Phys. Lett. 314, 443-450 (1999) and references
cited therein.
DUMBO
DUMBO (Decoupling Uses Mind Boggling Optimization) is a phase modulation
scheme where the phase modulation is described in terms of a Fourier series
The shape can be created using the AU-program DUMBO. The DUMBO shape
file in the release version of TOPSPIN is calculated for 32 µs pulses. To create
your own DUMBO shape you can also use the au-program dumbo. See instruc
tions in the header of the au-program for proper use.
The above pulse program to observe J-couplings with DUMBO decoupling would
be written as follows:
define loop counter count;calculate number of LG periods according to aq
-
"count=aq/(p10)"
.
3 (p10:sp1 ph3):f2 ;p10 set by AU-program DUMBO (n*32 µsec)
lo to 3 times count
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Decoupling Techniques
References:
1. D. Sakellariou, A. Lesage, P. Hodgkinson, and L. Emsley, Homonuclear dipolar decoupling in solid-
state NMR using continuous phase modulation, Chem. Phys. Lett. 319, 253-260 (2000).
2. Lyndon Emsley’s home page: http://www.ens-lyon.fr/STIM/NMR/NMR.html
Transverse Dephasing Optimized Spectroscopy 5.3
Decoupling optimized under refocused conditions:
Figure 5.6. Pulse Program for Hahn Echo Sequence
Transverse Dephasing Optimized spectroscopy (G. De Paepe et al. 2003) uses a
spin echo sequence for optimizing heteronuclear decoupling. The idea behind it is
simply the removal of the normally dominant J
line broadening effects) in the transverse relaxation rate R
8). With the normal CP experiment the observed line broadening (coherence de
cay time T
*
) might be caused by other heterogeneous effects, such as distribu-
2
term (describing coherent residual
0
(A. Abragam chapter
2
tion of chemical shifts or susceptibility effects and not reflect the true T’
(coherence lifetime). The true T’2 achieved through good heteronuclear decoupling can then be observed with a hahn-echo experiment. Optimization is done by
looking for the maximum signal amplitude of the decoupled resonances of inter
est. Be careful not to exceed the maximum decoupling time with high power decoupling.
Reference:
1. G. De Paepe, N. Giraud, A. Lesage, P. Hodgkinson, A. Böckmann, and L. Emsley, Transverse Dephasing Optimized Solid-State NMR Spectroscopy, JACS 125, 13938 – 13939 (2003).
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2
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Practical CP/MAS
Spectroscopy on
6
Spin 1/2 Nuclei 6
Once good setup parameters have been obtained to observe 13C and get good S/
N on glycine, it should be easy to also observe
samples and on nuclei different from
across samples where it is difficult to observe
gies to optimize acquisition parameters for 13C and other spin ½ nuclei.
Possible Difficulties 6.1
Usually, 13C spectra are easily acquired. Several sample properties may however
make observation difficult:
1. Low concentration of 13C in the sample.
2. No or too few protons in the sample.
13
C. Nevertheless, sometimes one comes
13
C-CP/MAS spectra on other
13
C. This chapter deals with strate-
3. Long proton T1.
4. Long T
5. Short proton T1ρ.
If a nucleus different from 13C should be observed, there are additional potential
difficulties:
6. Unknown chemical shift.
7. Unknown Hartmann-Hahn-condition.
8. Unknown relaxation properties (proton T1, T1ρ, T
Possible Approaches for 13C Samples 6.2
1.Collect as much information about the sample as possible. Do not accept samples
for measurement with unknown composition. Request information about:
- possible hazards (upon a rotor explosion)
- concentration of the nucleus to be measured
- structural information about the molecular environment of the nucleus of interest:
- mobility (rigid environment: expect long T1 and repetition delay),
- proximity to protons (can one use cross polarization)
I-S
.
).
I-S
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Practical CP/MAS Spectroscopy on Spin 1/2 Nuclei
- conductivity, dielectric loss (expect tuning and RF-heating problems if sample
is dielectrically lossy or even conductive)
2. Collect information about the sample first by running an “easy” nucleus:
Feasibility of cross polarization parameters is the required key information, because it decides the steps to follow.
If the sample information which you have collected shows that a 13C CP/MAS
experiment should be feasible (sample contains more than 20% protonated
carbons), load a reference cross polarization data set (S/N test spectrum of
glycine), spin the sample at the same spin rate, set contact time (p15) to 1ms,
wait 1 min., do one scan. There should be a visible signal.
From there on, optimize the required repetition rate (d1), contact time (p15),
number of scans (ns), spin rate (masr) and Hartmann-Hahn adjustment until
the signal is optimum. In very few cases, the decoupler offset (o2) may require
readjustment.
If no 13C-signal is found, the reasons may be:
- incorrect setup (recheck reference sample)
- concentration lower than expected
- unusual relaxation properties (long T
3. Then the most important information about the sample (proton T1, proton T1ρ)
can be obtained by looking at the protons in the sample. Set up for proton ob
servation, set swh to 100000-500000, rg to 4 and pulprog cpopt (if not found
in the library, copy the pulse program in the appendix), p3 and pl12 for
p3=p90. Set spnam0 = ramp.100, sp0 = power level for HH, p15 =100 us. Do
1 scan and fourier transform/phase correct. Using popt, optimize d1 for maxi
mum signal.
long proton T1, short proton T1ρ).
I-S,
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-
Note: CP/MAS probes usually have a substantial proton background signal. Do not be misled by this, it will not behave like a regular signal:
- it will grow steadily with longer pulses
- it will not show spinning sidebands
- it will cancel when a background suppression pulse program like aring is
used with a full phase cycle.
4. Knowing the required relaxation delay, the following step is to determine the
cross polarization (contact time). On protons, we measure the time constant
T1ρ. Using popt in the previous setup, vary p15 between 100 µsec and 10 ms
(even 20 ms at reduced power, if a long T
is expected, as the distance be-
I-S
tween nucleus of interest is long or the mobility is high, leading to a small heteronuclear dipolar coupling between nucleus of interest and protons). This
measurement will tell you how long the contact time p15 may be. A value of
p15 giving 50% of the initial proton signal amplitude will still give a 2-fold en
hancement on 13C. If the proton signal is below 50% at 1ms spin lock time or
even less, a full cp-enhancement cannot be expected.
5. Now we know the minimum relaxation delay and the maximum contact time.
With these parameters used as d1 and p15, the measurement is just a matter
of patience.
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