CORTECS 2.7 µm Columns
CONTENTS
I. INTRODUCTION
II. GETTING STARTED
a. Column Connection
b. Column Installation
c. Minimizing Band Spread Volume
d. Measuring Band Spread Volume
e. Measuring System Dwell Volume
f. Column Equilibration
g. eCord™ Installation
h. Functional Tests for Benchmarking a New Column
i. VanGuard™ Pre-Columns
III. COLUMN USE
a. Sample Preparation
b. pH Range
c. Solvents
d. Pressure
e. Temperature
I. INTRODUCTION
Thank you for choosing a Waters CORTECS Column. CORTECS 2.7 µm
Columns are based on the same solid-core particle technology
as CORTECS UPLC® 1.6 µm Columns, enabling seamless method
transfer between HPLC, UHPLC and UPLC platforms. All CORTECS
Columns are manufactured in cGMP, ISO 9001:2000 certified
facilities. Strict quality procedures for the manufacture of
the solid-core particle, the bonded phase synthesis, and the
column packing result in a high quality and reproducible final
product. Every column is individually tested and a Performance
Chromatogram and Certificate of Batch Analysis are provided on
the eCord Intelligent Chip. The eCord is available on all 2.1 mm
and 3.0 mm column dimensions.
CORTECS 2.7 µm Columns will exhibit maximum chromatographic
®
performance when used on a member of the ACQUITY UPLC
System family.
IV. COLUMN CLEANING, REGENERATION
AND STORAGE
a. Cleaning and Regeneration
b. Storage for Reversed-Phase and HILIC columns
V. ECORD INTELLIGENT CHIP TECHNOLOGY
a. Introduction
b. Installation
c. Column Use Information
VI. ADDITIONAL INFORMATION
a. Tips for Maximizing Column Lifetime
b. Getting Started with CORTECS® HILIC Columns
c. Troubleshooting Questions
II. GET TING STARTED
Each CORTECS 2.7 µm Column comes with a Certificate of
Analysis, which includes the bonded phase batch number and
the analytical test results for the unbonded and bonded particle.
The included Performance Test Chromatogram summarizes
the performance of each individual column and provides batch
number, column serial number, USP plate count, USP tailing
factor, retention factor, and chromatographic test conditions.
These data should be recorded and stored for future reference.
When available, the information can be accessed via the ACQUITY
UPLC Console using the attached eCord.
a. Column Connection
CORTECS 2.7 µm Columns are designed to operate on any HPLC,
UHPLC, or UPLC system. Due to the absence of an industry
standard, be aware that the type of fittings and connection on
each system will vary by manufacturer. All tubing connections
must be reseated to match the new column when it is installed.
If the style of the column endfitting does not properly match the
system connections, the chromatographic performance of your
new column will be negatively impacted, or leaking can occur.
c. Minimizing Band Spread Volume
Band spreading is the measurement of the system dispersion,
which impacts the chromatographic performance. Internal tubing
diameter and fluidic connections can significantly impact system
band spreading and chromatographic performance. Larger
tubing diameters cause excessive peak broadening and reduced
sensitivity (Figure 1).
0.005 inches
0.020 inches
0.040 inches
Diluted/Distorted Sample Band
Figure 1. Impact of Tubing Diameter on Band Spread.
d. Measuring Band Spread Volume
This test should be performed on a liquid chromatographic system
equipped with a UV detector.
b. Column Installation
Note. The flow rates given in the procedure below are described for
a 2.1 mm i.d. column. Adjust the flow rate up or down based on the
column pressure and system limits.
1. Purge the pumping system of any buffer-containing mobile
phases using 100 % HPLC-grade water.
2. Purge the pumping system to 100% organic mobile phase
(methanol or acetonitrile).
3. Connect the inlet of the column to the chromatographic system.
4. Flush the column with 100% organic mobile phase (methanol
or acetonitrile) by setting the pump flow rate to 0.1 mL/min.
Increase the pump flow rate to 0.5 mL/min over 5 minutes.
5. Once the mobile phase is flowing from the column outlet, stop
the flow.
6. Attach the column outlet to the detector. This prevents air
entering the detector flow cell.
7. Increase the flow rate as described in step 4.
8. Monitor until a steady backpressure and baseline have
been achieved.
1. Disconnect the column from the system and replace with a zero
dead volume union.
2. Set the flow rate on the pumping system to 1 mL/min.
3. Use a test mixture (dissolved in the mobile phase conditions)
that delivers a maximum peak height of less than 0.5 AU.
4. Inject 2–5 µL of this solution.
5. Using the 5-Sigma method, measure the peak width in minutes
at 4.4% of peak height:
System Volume
4.4% h
Figure 2. Determination of System Band Spread Volume using 5-Sigma method.
Band Spreading (µL) = Peak Width (min) x Flow Rate (µL/min)
(For example, If peak width = 0.1 min and flow rate = 1000 µL/min,
band spread = 100 µL)
CORT ECS 2.7 µm Columns
2
Table 1. Expected System Band Spread Volumes for Waters
LC Systems
Recommended
CORTECS Column i.d.
System
Alliance
Band
Spread
®
2695 HPLC 29 µL 4.6 mm 3.0 mm
1st
Choice
2nd
Choice
ACQUITY UPLC 12 µL 2.1 mm 3.0 mm
ACQUITY UPLC H-Class 9 µL 2.1 mm 3.0 mm
ACQUITY UPLC I-Class (FTN) 7.5 µL 2.1 mm 3.0 mm
ACQUITY UPLC I-Class (FL) 5.5 µL 2.1 m m 1.0 mm
Non-Waters UHPLC System 15–25 µ L 3.0 mm 2.1 mm
e. Measuring System Dwell Volume
Dwell volume is different than system band spreading. System
dwell volume is a measurement of the volume it takes for the
initial gradient conditions to reach the head of the column. This
value is necessary when transferring a method between different
chromatographic systems.
Programmed time = 5.00 minutes
0.70
0.65
0.60
0.55
0.50
0.45
0.40
AU
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Figure 3. Measuring System Dwell Volume.
50%
0 2 4 6 8 10 12 14 16 18 20 min
Flow Rate = 1.5 mL/min
5.69 minutes
- 5.00 minutes
0.69 minutes
Time = 5.69 minutes
System Volume:
0.69 min x 1.5 mL/min = 1.04 mL
Table 2. Expected System Dwell Volumes for Waters Systems
System Dwell Volume
Alliance 2695 HPLC 900 µL
ACQUITY UPLC 120 µ L
ACQUITY UPLC H-Class 350 µL
ACQUITY UPLC I-Class (FTN) 100 µ L
ACQUITY UPLC I-Class (FL) 95 µL
1. Disconnect the column from the system and replace with a zero
dead volume union.
2. Use acetonitrile as mobile phase A, and acetonitrile containing
0.05 mg/mL uracil as mobile phase B.
3. Use the flow rate in the original method and the intended flow
rate on the target instrument.
4. Collect detector baseline using 100% mobile phase A for
5 minutes.
5. At 5.00 minutes, program a step to 100% mobile phase B,
and collect data for an additional 5 minutes.
6. Measure absorbance difference between 100% A and 100% B.
7. Measure time at 50% of that absorbance difference.
8. Calculate time difference between start of step and 50% point.
9. Multiply time difference by the flow rate to calculate
system volume.
f. Column Equilibration
CORTECS 2.7 µm Columns are shipped in 100% acetonitrile. It is
important to ensure mobile phase compatibility before changing
to a different mobile phase system. To avoid precipitating mobile
phase buffers within the column or system, flush the column with
five column volumes of a waters/organic solvent mixture, using
the same, or lower, solvent content as in the desired buffered
mobile phase (for example, flush the column and system with 60%
methanol in water prior to introducing 60% methanol/40% buffer
mobile phase).
Note. If mobile phase additives (i.e., ion-pairing reagents) are
present in low concentrations (<0.2% v/v), 100 to 200 column
volumes may be required for complete equilibration. In addition,
mobile phases that contain formate (i.e., ammonium formate,
formic acid) may require extended equilibration times.
For reversed-phase separations, equilibrate the column with a
minimum of 10 column volumes of the mobile phase to be used
(refer to Table 3 for a list of column volumes). The column may be
considered fully equilibrated once a constant backpressure and a
stable detector baseline is achieved.
CORT ECS 2.7 µm Columns
3
Table 3. Empty Column Volumes (mL)
Internal Column Diameter
Column Length (mm) 1.0 mm 2.1 mm 3.0 mm 4.6 mm
30 0.024 0.10 0.21 0.50
50 0.039 0.17 0.35 0.83
75 0.059 0.26 0.53 1.25
100 0.079 0.35 0.71 1.66
150 0.12 0.53 1.07 2.49
For CORTECS HILIC Columns, flush with 50 column volumes of
50:50 acetonitrile/water with 10 mM final buffer concentration.
Prior to the first injection, equilibrate with 20 column volumes
of initial mobile-phase conditions (refer to Table 1 for a list of
column volumes). If gradient conditions are used, equilibrate
with 8–10 column volumes between injections. Failure to
appropriately equilibrate the column could results in drifting
retention times. See “Getting Started with CORTECS HILIC
Columns” under “Additional Information”.
g. eCord Installation
eCord Technology represents a significant advancement in column
usage tracking management when connected to an ACQUIT Y UPLC
System. The eCord Intelligent Chip can be read by connecting the
yellow fob to the reader/writer located on the right hand side of
the ACQUITY UPLC Column heater module. Embedded information
such as the column manufacturing QC data and Certificates of
Analysis may be accessed via the ACQUITY UPLC console. The
eCord is available on all 2.1 mm, and 3.0 mm column dimensions.
h. Functional Tests for Benchmarking a New Column
Waters recommends performing a benchmarking test upon receipt
of your column and throughout lifetime usage. By using a standard
mix such as the appropriate Quality Control Reference Material
(QCRM), you can:
Verify the performance of your column upon receipt
2. Repeat test daily to track column and system performance
over time.
For more information on benchmarking performance, visit
www.waters.com/QCRM
Note. If an analyte mixture found in the Performance Test
Chromatogram is used to benchmark, the isocratic efficiencies
measured in your laboratory may be less than those given on
the Waters Performance Test Chromatogram. This is normal
and expected. The Waters isocratic column testing systems
have been modified in order to achieve extremely low system
dispersion. This presents a more challenging test of how well
the column was packed. This also guarantees the highest
quality packed column. These special testing systems have
been modified to such an extent that they are not commercially
viable and have limited method flexibility other than isocratic
column testing.
3. Determine the number of theoretical plates (N) and use this
value for periodic comparisons.
4. Repeat the test periodically to track column performance
over time. Slight variations may be obtained on different
LC systems due to the quality of the connections, operating
environment, system electronics, reagent quality, column
condition, and operator technique.
i. VanGuard Pre-Columns
VanGuard Pre-Columns are designed to be attached directly to the
inlet of a CORTECS Analytical Column. They are 2.1 mm i.d. x 5 mm
length guard columns packed with CORTECS solid-core silica
particles. The chemistries offered for VanGuard Pre-Columns are
identical to the available CORTECS chemistries.
Note. VanGuard Pre-Columns are shipped with a collet and ferrule that
are NOT pre-swaged. This enables the end user to seat the VanGuard
Pre-Column to the specific CORTECS Column to ensure void-free and
leak-free connections. Care must be taken when removing the O-ring
that holds these two pieces on the pre-column tubing.
CORT ECS Column
VanGuard Pre-Column
Monitor the health of your column and system over time
Troubleshoot separation difficulties that arise
The Neutrals QCRM (p/n 186006360) or HILIC QCRM (p/n
186007226) are appropriate mixtures with which to benchmark
your CORTECS Column and System. Other QCRMs are available
depending on the application and detection mode.
1. Run an initial benchmark test to monitor key performance
criteria such as retention time, peak area, peak tailing,
resolution, response, system pressure, etc.
Place wrench here
Ferrule
Flow
Figure 4. Installing a VanGuard Pre-Column.
CORT ECS 2.7 µm Columns
Collet
Place wrench here
4
VanGuard Pre-Column Installation Instructions
1. Remove the VanGuard Pre-Column from its box and shipping
tube and remove the plastic plug.
2. Orient the pre-column so that the male end is facing up and
carefully remove the black O-ring that holds the collet and
ferrule in place during shipment (collet and ferrule are not
permanently attached).
3. Orient the CORTECS Column perpendicular to the work surface
so that the column inlet is on the bottom.
4. From below, insert the VanGuard Pre-Column into the column
inlet; turn the assembled column and pre-column 180 °C so
that the pre-column is now on top.
5. Tighten with two 5/16” wrenches placed onto the CORTECS
Column flats and VanGuard Pre-Column hex nut (male end) as
shown in Figure 4.
6. While keeping pressure on the VanGuard Pre-Column against the
CORTECS Column, tighten ¼ turn to set the collet and ferrule.
7. Check that the ferrule is set by loosening the connection and
inspecting the ferrule depth.
8. Reattach (Steps 4–6) the pre-column and apply flow to inspect
for leaks.
3. If the sample is not prepared in the mobile phase, ensure that
the sample, solvent and mobile phases are miscible in order to
avoid sample precipitation or buffer precipitation.
4. Filter sample with a 0.2 µm membrane to remove particulates.
If the sample is dissolved in a solvent that contains an organic
modifier (e.g., acetonitrile, methanol, etc.) ensure that the
membrane material is compatible with the solvents in use.
Alternatively, centrifuge the sample for 20 minutes at
8,000 RPM, followed by the transfer of the supernatant to an
appropriate vial.
5. For hydrophilic-interaction chromatography (HILIC) separations,
the samples must be prepared in a high percentage of organic
solvent (e.g., 95% acetonitrile). See “Getting Started with
CORTECS HILIC Columns”.
b. pH Range
Table 4. Recommended pH Range for CORTECS Columns
Chemistry pH Range
CORTECS 2.7 µm, C
CORTECS 2.7 µm, C
18
+ 2–8
18
CORTECS 2.7 µm, HILIC 1–5
2–8
III. COLUMN USE
To ensure the continued high performance of CORTECS 2.7 µm
Columns, follow these guidelines:
a. Sample Preparation
1. Sample impurities and/or particulates often contribute
to column contamination. One option to avoid column
contamination is to use Waters Oasis® or Sep-Pak® solid-phase
extraction (SPE) devices. To select the appropriate sorbent for
a specific sample type, visit www.waters.com/sampleprep
2. It is preferable to prepare the sample in the initial mobile
phase conditions or a weaker solvent for the best peak shape
and sensitivity.
Column lifetime will vary depending on the combination of
temperature, mobile phase pH and type of buffer or additive
used. Table 5 lists the recommended buffers and additives for
CORTECS Columns.
Note. Working in combinations of extreme pH, temperature, and
pressure may result in reduced column lifetime.
CORT ECS 2.7 µm Columns
5
Table 5. Mobile Phase Buffer Recommendations for CORTECS 2.7 µm Columns
Additive/Buffer pK
TFA 0.30 Volatile Yes
Acetic Acid 4.76 Volatile Yes
Formic Acid 3.75 Volatile Yes
Acetate
4CH2
COOH)
(NH
Formate
(NH4COOH)
Phosphate 1 2.15 1.15 – 3.15 Non-volatile No Traditional low pH buffer, good UV transparency.
Phosphate 2 7.2 0 6.20– 8.20 Non-volatile No
4.76
3.75
Buffer
a
Range
3.76
– 5.76
2.75
– 4.75
Volatility (±1 pH unit)
Volatile Yes
Volatile Yes
c. Solvents
To maintain maximum column performance, use high quality HPLC
or MS grade solvents. Filter all aqueous buffers prior to use through
a 0.2 µm filter. Solvents containing suspended particulate materials
will generally clog the outside surface of the inlet of the column.
This may result in higher backpressure or distorted peak shape.
d. Pressure
CORTECS 2.7 µm Columns are compatible with HPLC, UHPLC,
and UPLC pressures. Table 6 provides the maximum operation
pressure for each column dimension.
Table 6. Maximum Operation Pressure
Column i.d. Maximum Operating Pressure
2.1 mm 15,000 PSI [1034 bar]
3.0 mm 15,000 PSI [1034 bar]
4.6 mm 9,000 PSI [620 bar]
e. Temperature
CORTECS 2.7 µm Columns can be used at temperatures up to 45 °C
to enhance selectivity, reduce solvent viscosity, and increase
mass transfer rates.
Used for
Mass Spec
Comments
Ion pair additive, can suppress MS signal, used in
the 0.02-0.10% range.
Maximum buffering obtained when used with
ammonium acetate salt. Used in 0.1-1.0% range.
Maximum buffering obtained when used with
ammonium formate salt. Used in 0.1-1.0% range.
Used in the 1-10 mM range. Note that sodium or
potassium salts are not volatile.
Used in the 1-10 mM range. Note that sodium or
potassium salts are not volatile.
Above pH 7, reduce temperature/concentration
and use a guard column to maximize lifetime.
IV. COLUMN CLEANING, REGENERATION, AND
STORAGE
a. Cleaning and Regeneration
Changes in peak shape, peak splitting, shouldering peaks, shifts in
retention, change in resolution, or increasing backpressure may
indicate contamination of the column. Flush with a neat organic
solvent to remove the non-polar contaminant(s), taking care not to
precipitate any buffered mobile phase components. If this flushing
procedure does not solve the problem, purge the column with the
following cleaning and regeneration procedures.
Use a cleaning routine that matches the properties of the samples
and stationary phase type (reversed-phase, normal-phase or
HILIC) to help solubilize the suspected contaminate. Flush with
20 column volumes of solvent at 45 °C. Return to the initial
mobile phase conditions by reversing the sequence.
If using a reversed-phase column, purge the column with a
sequence of progressively more non-polar solvents (i.e., water-to-
methanol-to-tetrahydrofuran-to-methylene chloride).
If using a HILIC column, purge the column with a sequence of
progressively more polar-organic solvents (i.e., acetonitrile-
to-acetonitrile/methanol-to-acetonitrile/water-to-water).
Note. Working in combinations of extreme pH, temperature and
pressure may result in reduced column lifetime.
If column performance has not improved after regeneration/
cleaning procedures, contact your local Waters representative for
additional support.
CORT ECS 2.7 µm Columns
6
b. Storage after Reversed-Phase and HILIC Use
For periods longer than four days, store the column in 100%
acetonitrile. For separations utilizing elevated temperature,
store immediately after use in 100% acetonitrile. Do not store
columns in buffered eluents. If the mobile phase contained a buffer
salt, flush the column with 10 column volumes of HPLC-grade
water (see Table 3 for column volume information) followed
by 10 column volumes of acetonitrile. Failure to perform this
intermediate step could result in precipitation of the buffer salt
in the column when 100% acetonitrile is introduced. Completely
seal the column to avoid solvent evaporation and drying out of the
chromatographic bed.
Note. If a column has been run with a formate-containing mobile
phase (e.g., ammonium formate, formic acid, etc.) and is purged
with 100% acetonitrile, slightly longer equilibration times may be
necessary when the column is re-installed and re-wetted with that
same formate-containing mobile phase.
b. Installation of the eCord
The eCord device can be read by connecting the yellow fob to the
heater compartment receptacle located on the right hand side
of the ACQUITY UPLC Column heater module. Once the eCord
is connected, column identification and overall column usage
information can be accessed.
Figure 6. Installing the eCord Intelligent Chip.
eCord Fob
c. Column Use Information
The eCord Intelligent Chip provides the user with specific column
information as well as column use data including; chemistry
type, column dimension, serial number and part number. The
overall column use information includes; total number of samples
injected, total number of injections as well as the maximum
pressure and temperature that the column has been exposed to.
Additionally, detailed column history includes the sample set
start date, user name and system name.
V. ECORD INTELLIGENT CHIP TECHNOLOGY
a. Introduction
The eCord Intelligent chip provides a paperless tracking history
of the column’s performance and usage throughout its lifetime.
The eCord is permanently attached to the column body via a
tether that cannot be removed. This ensures that the history of the
column is always accessible to the user of that column. The eCord
Intelligent Chip is available on CORTECS Columns with 2.1 mm
and 3.0 mm inner dimensions.
Waters eCord -
intelligent chip
Figure 5.: eCord Intelligent Chip Identification.
At the time of manufacture, the Performance Test Chromatogram,
analytical data for the particles, and Certificate of Batch Analysis
is downloaded onto the eCord. This information may then be
accessed via the ACQUITY UPLC console once the column is
installed.
VI. ADDITIONAL INFORMATION
a. Tips for Maximizing Column Lifetime
1. To maximize column lifetime, pay close attention to:
Water quality (including water purification systems)
Solvent quality
Mobile phase preparation, storage, and age
Sample, buffer, and mobile phase solubility
Sample quality and preparation
2. When problems arise, systematically troubleshoot potential
cause one variable at a time in a systematic fashion.
3. Always remember to:
Use an in-line filter unit (part number 205000343) or a
suitable Vanguard Pre-Column.
Discourage bacterial growth by minimizing the use of
100% aqueous mobile phases where possible.
To reduce the chances of mobile phase contamination
or degradation, prepare enough mobile phase to last for
3–4 days. Alternatively, store excess bulk quantities in a
refrigerated environment.
Discard and re-prepare aqueous mobile phase every
24–48 hours (if 100% aqueous mobile phase is required).
Add 5–10% organic modifier to aqueous buffer to minimize
bacterial growth (adjust gradient profile as necessary).
Filter aqueous portions of mobile phase through a
0.2 µm filter.
CORT ECS 2.7 µm Columns
7
Routinely maintain your water purification system to
ensure it is functioning properly.
Only use ultra-pure water (18 ΩOhm-cm) and highest
quality solvent possible.
Consider sample preparation (e.g., SPE, filtration,
centrifugation, etc.) when possible.
4. Avoid when possible:
100% aqueous mobile phases
HPLC-grade bottled water
“Topping off” your mobile phases
Using phosphate salt buffer in combination with
high acetonitrile concentrations (e.g., >70%) due to
precipitation.
Injection Solvent considerations:
1. Whenever possible, injection solvents should contain 95%
acetonitrile with the polar solvent (i.e., water, methanol,
isopropanol) component to be no more than 25% of the total
volume. A generic injection solvent is 75:25 acetonitrile/
methanol. T his is a good compromise between analyte
solubility and peak shape.
2. Avoid water and dimethylsulfoxide (DMSO) in the injection
solvents. These solvents will produce very poor peak shapes.
In HILIC, it is important to remember that water is the
strongest eluting solvent. Therefore, it must be eliminated or
minimized in the injection solvent. Exchange water or DMSO
with acetonitrile by using reversed-phase SPE. If this is not
possible, dilute the water or DMSO with organic solvent.
b. Getting Started with CORTECS HILIC Columns
Note. CORTECS HILIC Columns are designed to retain very polar
bases. Acidic, neutral, and/or non-polar compounds will have
limited retention
Mobile-Phase Considerations:
1. Always maintain at least 3% polar solvent, such as water, in
the mobile phase or gradient. This ensures that the CORTECS
HILIC Particle is always hydrated.
2. Maintain at least 40% organic solvent (e.g., acetonitrile) in
your mobile phase or gradient.
3. Avoid phosphate salt buffers to avoid precipitation in high
organic content mobile phases used for HILIC separations.
Phosphoric acid is acceptable.
4. Buffered mobile phases such as ammonium formate or
ammonium acetate will produce more reproducible results
compared to unbuffered additives such as formic acid or acetic
acid. For best peak shape, maintain a buffer concentration of
10 mM.
5. If using an ACQUIT Y UPLC System, the weak needle wash
solvent should closely match the % organic present in the
initial mobile-phase conditions, otherwise, analyte peak shape
distortion can occur.
c. Troubleshooting Questions
1. Are you using 100% aqueous mobile phases?
2. What is the age of the mobile phase?
3. Is the mobile phase filtered through a 0.2 µm membrane?
4. Was the mobile phase prepared fresh or topped off?
5. Is the water source of adequate quality?
6. When was the last time the water system was serviced or
was the bottle of
water unopened?
7. Is bacterial growth a possibility (pH7 phosphate buffer is
susceptible to bacterial growth within 24 hours)?
8. If a neat standard is prepared in the initial mobile phase
conditions and injected, are the problems still observed?
9. If the sample is filtered/purified (i.e., SPE, filtration...etc.) is
the problem still observed?
10. Has the quality of the samples changed over time?
Waters, The Science of W hat’s Possible, CORTECS, UPLC, ACQUITY UPLC, Alliance, Oasis, and Sep-Pak are registered trademarks of Waters
Corporation. eCord and VanGuard are trademarks of Waters Corporation. All other trademarks are property of their respective owners.
©2014 Waters Corporation. Produced in the U.S.A. May 2014 720005024EN KP-P DF
Waters Corporation
34 Maple Street
Milford, MA 01757 U.S.A.
T: 1 508 478 2000
F: 1 508 872 1990
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