Dionex DX-120 Operator's Manual

DX-120 ION CHROMATOGRAPH

OPERATOR’S MANUAL

© 1998 Dionex Corporatio n

Document No . 031183

Revision 03

September 1998

©1998 by Dionex Corpor ation
All rights reserved worldwide.
Printed in the United States of America.

This publication is protected by federal copyright law. No part of this publication
may be copied or distributed, transmitted, transcribed, stored in a retrieval system,
or transmitted into any human or computer language, in any form or by any means,
electronic, mechanical, magnetic, manual, or otherwise, or disclosed to third parties
without the express written permission of Dionex Corporation, 1228 Titan Way,
Sunnyvale, California 94088-36 03 U.S.A.

DISCLAIMER OF WARRANTY AND LIMITED WARRANTY

THIS PUBLICATION IS PROVIDED “AS IS” WITHOUT WARRANTY OF
ANY KIND. DIONEX CORPORATION DOES NOT WARRANT,
GUARANTEE, OR MAKE ANY EXPRESS OR IMPLIED
REPRESENTATIONS REGARDING THE USE, OR THE RESULTS OF THE
USE, OF THIS PUBLICATION IN TERMS OF CORRECTNESS,
ACCURACY, RELIABILITY, CURRENTNESS, OR OTHERWISE.
FURTHER, DIONEX CORPORATION RESERVES THE RIGHT TO REVISE
THIS PUBLICATION AND TO MAKE CHANGES FROM TIME TO TIME
IN THE CONTENT HEREINOF WITHOUT OBLIGATION OF DIONEX
CORPORATION TO NOTIFY ANY PERSON OR ORGANIZATION OF
SUCH REVISION OR CHANGES.

EMISSIONS COMPLIANCE

This equipment meets ITE standard EN 55022 part A for radiated emissions and is
suitable for use in a laboratory environment. Operation of this equipment in a
residential area, however, may cause interference to radio and television reception.

TRADEMARKS

Teflon® an d Tefzel® are registered t rademarks of E.I. du Pont de Ne mours & Co.
AutoSuppression, DX-LAN, IonSep®, MPIC®, OmniPac®, OnGuard,
Self-Regenerating Suppressor, and SRS  are trademarks of Dionex Corp.

PRINTING HISTORY

Revision 01, May 1996
Revision 02, March 1997
Revision 03, September 1998

Contents

1 • Introduction

1.1 About This Manual . . . . . . . . . . . . . . . . . 1-2

1.1.1 Typefaces and Conventions . . . . . . . . 1-3

1.1.2 Safety Messages and Notes . . . . . . . . 1-4

1.1.3 Symbols . . . . . . . . . . . . . . . . . . . 1-5

1.2 Related Manuals . . . . . . . . . . . . . . . . . . . 1-5

2 • Description

2.1 Operating Features . . . . . . . . . . . . . . . . . 2-1

2.1.1 Front Control Panel . . . . . . . . . . . . 2-3

2.1.2 Pump . . . . . . . . . . . . . . . . . . . . 2-6

2.1.3 Configuration DIP Switches . . . . . . . 2-6

2.1.4 Eluent Reservoirs . . . . . . . . . . . . . 2-7

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2.1.5 Component Panel . . . . . . . . . . . . . 2-8

2.1.6 Rheodyne Injection Valve . . . . . . . . . 2-11

2.1.7 Detector Cells . . . . . . . . . . . . . . . 2-12

2.1.8 DS4 Detection Stabilizer . . . . . . . . . 2-13

2.2 Dual-Column Configuration Features . . . . . . . 2-15

2.2.1 Column Select Mode . . . . . . . . . . . 2-16

2.2.2 Eluent Select Mode . . . . . . . . . . . . 2-18

2.3 Fluid Schematics . . . . . . . . . . . . . . . . . . 2-19

2.4 Control Modes . . . . . . . . . . . . . . . . . . . . 2-22

2.4.1 Local Mode . . . . . . . . . . . . . . . . . 2-22

2.4.2 Remote Mode . . . . . . . . . . . . . . . 2-22

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DX-120 Operator’s Manual

2.5 TTL Control . . . . . . . . . . . . . . . . . . . . . 2-23

2.5.1 Injection Valve/Remote Start Control . . 2-23

2.5.2 Recorder Range Control . . . . . . . . . . 2-23

3 • Operation and Maintenance

3.1 Preparing Eluents . . . . . . . . . . . . . . . . . . 3-1

3.1.1 Degassing Eluents . . . . . . . . . . . . . 3-1

3.1.2 Filtering Eluents . . . . . . . . . . . . . . 3-2

3.1.3 Pressurizing Eluent Reservoirs . . . . . . 3-2

3.2 Preparing Samples . . . . . . . . . . . . . . . . . 3-3

3.2.1 Collecting and Storing . . . . . . . . . . . 3-3

3.2.2 Pretreating . . . . . . . . . . . . . . . . . 3-3

3.2.3 Diluting . . . . . . . . . . . . . . . . . . . 3-4

3.3 Operating . . . . . . . . . . . . . . . . . . . . . . 3-5

3.3.1 Starting Up . . . . . . . . . . . . . . . . . 3-5

3.3.2 Injecting the Sample . . . . . . . . . . . . 3-7

3.4 Using an Integrator . . . . . . . . . . . . . . . . . 3-9

3.5 Running under PeakNet Control . . . . . . . . . . 3-9

3.6 Optimizing Temperature Compensation . . . . . . 3-10

3.6.1 With a DS4 . . . . . . . . . . . . . . . . . 3-10

3.6.2 With a CDM-3 Cell . . . . . . . . . . . . 3-10

3.7 Maintenance . . . . . . . . . . . . . . . . . . . . . 3-11

4 • Troubleshooting

4.1 Alarms . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2 Error Codes . . . . . . . . . . . . . . . . . . . . . 4-3

4.3 Liquid Leaks . . . . . . . . . . . . . . . . . . . . . 4-4

4.4 Pump Difficult to Prime . . . . . . . . . . . . . . 4-8

ii

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4.5 Pump Loses Prime . . . . . . . . . . . . . . . . . 4-8

4.6 Pump Does Not Start . . . . . . . . . . . . . . . . 4-9

4.7 No Flow . . . . . . . . . . . . . . . . . . . . . . . 4-9

4.8 Excessive System Backpressure . . . . . . . . . . 4-9

4.9 Peak “Ghosting” . . . . . . . . . . . . . . . . . . . 4-10

4.10 Nonreproducible Peak Height or Retention

Time . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4.11 Abnormal Retention Time or Selectivity . . . . . 4-11

4.12 DS4 Temperature Inaccurate . . . . . . . . . . . . 4-12

4.13 No Detector Response . . . . . . . . . . . . . . . 4-13

4.14 Low Detector Output . . . . . . . . . . . . . . . . 4-14

4.15 High Detector Output . . . . . . . . . . . . . . . . 4-14

4.16 Noisy or Drifting Baseline . . . . . . . . . . . . . 4-15

5 • Service

Contents

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5.1 Replacing Tubing and Fittings . . . . . . . . . . . 5-2

5.2 Changing the Sample Loop . . . . . . . . . . . . 5-2

5.3 Isolating a Restriction in the Liquid Plumbing . . 5-3

5.4 Replacing the DS4 Cell . . . . . . . . . . . . . . . 5-3

5.5 Cleaning Cell Electrodes . . . . . . . . . . . . . . 5-5

5.6 Calibrating the Cell Constant . . . . . . . . . . . 5-6

5.7 Calibrating the Pump Flow Rate . . . . . . . . . . 5-8

5.8 Cleaning and Replacing Pump Check Valves . . . 5-8

5.9 Replacing a Pump Piston Seal . . . . . . . . . . . 5-9

5.10 Replacing a Pump Piston . . . . . . . . . . . . . . 5-12

5.11 Replacing the Pressure Transducer Waste

Valve O-Ring . . . . . . . . . . . . . . . . . . . . 5-14

5.12 Changing the Main Power Fuses . . . . . . . . . . 5-15

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DX-120 Operator’s Manual

A • Specifications

A.1 Electrical . . . . . . . . . . . . . . . . . . . . . . . A-1

A.2 Environmental/Physical . . . . . . . . . . . . . . . A-1

A.3 Control Panel . . . . . . . . . . . . . . . . . . . . A-2

A.4 Pump . . . . . . . . . . . . . . . . . . . . . . . . . A-2

A.5 Pulse Damper . . . . . . . . . . . . . . . . . . . . A-2

A.6 Detector . . . . . . . . . . . . . . . . . . . . . . . A-2

A.7 Conductivity Cell . . . . . . . . . . . . . . . . . . A-3

A.8 DS4 Detection Stabilizer (Optional) . . . . . . . . A-3

A.9 Valves . . . . . . . . . . . . . . . . . . . . . . . . A-3

A.10 Delay Volume . . . . . . . . . . . . . . . . . . . . A-4

B • Installation

B.1 Facility Requirements . . . . . . . . . . . . . . . . B-1

iv

B.2 Installation Overview . . . . . . . . . . . . . . . B-1

B.3 Rear Panel Connections . . . . . . . . . . . . . . B-2

B.3.1 Power Connection . . . . . . . . . . . . . B-2

B.3.2 Switched AC Outlet Connection

(Optional) . . . . . . . . . . . . . . . . . . B-4

B.3.3 Waste Lines . . . . . . . . . . . . . . . . . B-5

B.3.4 Gas Connection . . . . . . . . . . . . . . B-5

B.3.5 DX-LAN Cable Connection (Optional) . B-6

B.4 Eluent Reservoir Connections . . . . . . . . . . . B-8

B.5 Pump Setup . . . . . . . . . . . . . . . . . . . . . B-8

B.5.1 Priming the Pump . . . . . . . . . . . . . B-8

B.5.2 Checking the Pump Flow Rate

Calibration . . . . . . . . . . . . . . . . . B-9

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Contents

B.6 Connections to Chromatography Components . . B-10

B.6.1 Backpressure Requirements . . . . . . . . B-12

B.6.2 Self-Regenerating Suppressor (SRS)

Installation . . . . . . . . . . . . . . . . . B-13

B.6.3 Column Installation . . . . . . . . . . . . B-17

B.7 TTL Control Connections (Overview) . . . . . . . B-19

B.7.1 TTL Inputs . . . . . . . . . . . . . . . . . B-19

B.7.2 TTL Outputs . . . . . . . . . . . . . . . . B-20

B.7.3 F errite Core Installation on TTL Output

Cables . . . . . . . . . . . . . . . . . . . . B-21

B.8 Autosampler Connections (Optional) . . . . . . . B-22

B.8.1 Autosampler Outlet Line Connection . . B-22
B.8.2 AS40 Automated Sampler Connections . B-22
B.8.3 AS3 500 Automated Sampler

Connections . . . . . . . . . . . . . . . . B-24

B.9 Recorder and Integrator Connectio ns

(Optional) . . . . . . . . . . . . . . . . . . . . . . B-27

C • Integrator Programming

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B.9.1 Chart Recorder Connections . . . . . . . B-27

B.9.2 4400 or 4600 Integrator Connections . . B-27

B.10 Configuration DIP Switch Settings . . . . . . . . B-29

B.11 DS4 Detection Stabilizer Installation . . . . . . . B-33

B.12 CDM-3 Cell Installation . . . . . . . . . . . . . . B-35

B.13 Injection Valve Connections . . . . . . . . . . . . B-36

B.14 Column Switching Valve Connections . . . . . . . B-37

B.15 DX-LAN Card Installation (Optional) . . . . . . . B-38

C.1 Integrator Power-up Configuration . . . . . . . . C-1

C.2 Setting Offsets . . . . . . . . . . . . . . . . . . . . C-2

C.3 Area Percent Mode . . . . . . . . . . . . . . . . . C-2

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DX-120 Operator’s Manual

C.4 Using DIALOG to Create a Method . . . . . . . . C-3

C.4.1 Time Functions . . . . . . . . . . . . . . . C-3

C.4.2 Creating a Method . . . . . . . . . . . . . C-4

C.5 BASIC Programming . . . . . . . . . . . . . . . . C-7

D • Conductivity Detection

D.1 How Conductivity Is Measured . . . . . . . . . . D-1

D.2 Conductivity of Solutions . . . . . . . . . . . . . D-2

D.2.1 Effect of Hydration Sphere and

D.2.2 Effect of Temperature on Condu ctivity . D-4

D.2.3 Species Detected by Conductivity . . . . D-5

D.2.4 Chemical Suppression . . . . . . . . . . . D-6

D.2.5 Eluents for Conductivity Detection . . . D-9

Solvent on Conductivity . . . . . . . . . . D-4

vi

E • Glossary

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1 • Introduction

The Dionex DX-120 Ion Chro matograph performs isocratic ion
analysis applications using conductivity detection. The DX-120 is an
integrated system, which includes a pump, detector, and injection
valve. The chromatography components, including the column(s),
Self-Regenerating Suppressor (SRS), and conductivity cell are
ordered separately. These components are moun ted on the inside of
the DX-120 door.

The DX-120 can be controlled locally, using the front panel keypad
and display, or remotely, from a PeakNet workstation. The PeakNet
workstation consists of a computer with a Dionex DX-LAN
interface card and PeakNet software (Release 4.30 or higher)
installed. Limited remote control is also available using TTL signals.

The DX-120 can be ordered as a single-column system or a
dual-column system. The dual-column system a llows switching
between two sets of columns (column select mode) or b etween two
eluents (eluent select mode). In the eluent select mode, the DX-120
can perform step gradients.



The following models are available:

Configuration Voltage/Line Frequency* Without

Single-column 115 VAC/60 Hz P/N 050100 P/N 050200

Dual-column 115 VAC/60 Hz P/N 050102 P/N 0502 02

*Must match the voltage and line frequency of the installation site’s
power source.

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With

DX-LAN

100 VAC/50 Hz P/N 050103 P/N 0502 03
230 VAC/50 Hz P/N 050106 P/N 0502 06

100 VAC/50 Hz P/N 050105 P/N 0502 05
230 VAC/50 Hz P/N 050108 P/N 0502 08

DX-LAN

1-1

DX-120 Operator’s Manual

1.1 About This Manual

Chapter 1

Introduction

Chapter 2

Description

Chapter 3

Operation and

Maintenance

Chapter 4

Troubleshooting

Chapter 5

Service

Appendix A

Specifications

Appendix B

Installation

Appendix C

Integrator

Programming

Introduces the DX-120 and explains the
conventions used in the manual, including
safety-related information.

Describes the DX-120 operating features, the
chromatographic fluid path, and the control
modes.

Provides operating and routine preventive
maintenance procedures.

Lists problems, with step-by-step procedures to
isolate and eliminate their sources.

Provides step-by-step instructions for routine
service and parts replacement procedures.

Lists the DX-120 specifications and installation
site requirements.

Describes how to install the DX-120.

Describes how to program a Dionex 4400 or
4600 integrator for automated control of the
DX-120.

1-2

Appendix D

Conductivity

Appendix E

Detection

Glossary

Describes conductivity detection and its
applications.

Defines terms commonly used in ion
chromatography.

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1.1 .1 Typefaces and Conventions

•

Capitalized bold type indicates a front panel button. For
example:

1 • Introduction

Press

•

Upper-case bold type indicates information displayed on

Pump

to turn on the pump.

the front panel screen. For example:

LEAK ALARM

•

Upper-case italic type indicates a grouping of front panel

displays when a leak occurs.

buttons. For example:
Use the buttons in the DISPLAY group to select the type

of information shown on-screen.

•

When a function can be controlled by a DIP switch
setting, the switch and position numbers are in
parentheses. For example:

(SW1-3) indicates DIP switch 1, position 3.
(SW2-5, 6, 7, 8) indicates DIP switch 2, positions 5, 6, 7,

and 8.

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1-3

DX-120 Operator’s Manual

1.1 . 2 Safety Mess ages and Notes

The DX-120 meets European, EMC, and safety requirements
per Council Directives 73/23/EEC and 89/336/EEC, EN
61010-1:1993 (safety), EN 5008 2-1:1992 (susceptibility), and
EN 55011:1991 (emissions). The TUV/CE and GS safety
label on the DX-120 attests to compliance with these
standards.

The DX-120 is designed for ion chromatography applications
and should not be used fo r any other purpose. If there is a
question regarding appropria te usage, contact Dionex before
proceeding.

This manual con tains warnings and precau tionary statements
that, when properly followed, can prevent personal injury
and/or damage to the instrument. Safety messages appear in
bold type and are accompanied by icons, as follows:

Indicates an imminently hazardous situation which, if not
avoided, will result in death or serious injury.

1-4

Indicates a potentially hazardous situation which, if not
avoided, could result in death or serious injury.

Indicates a potentially hazardous situation which, if not
avoided, may result in minor or moderate injury.

Indicates that the function or process of the instrument
may be impaired. Operation does not constitute a hazard.

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Informational messages also appear throughout this manu al.
These are label ed NOTE and are in bold type:

NOTES call attention to certain information. They alert
you to an unexpected result of an action, suggest how to
optimize instrument performance, etc.

1.1.3 Symbols

The symbols below appear on the DX-120, or on DX-120
labels.

1 • Introduction

NOTE

~

Alternating current

Protective conductor terminal

Power supply is on

Power supply is off

1.2 Related Manuals

During installation and operation of the DX-120, you may need to
refer to one or more of the following manuals for information about
other components or instru ments in the system.

4440 Integrator User’s Guide (Document No. 034200) or 4600

•

Integrator User’s Guide (Document No. 034408)
AS40 Automated Samp ler Operator’s Manual (Document

•

No. 034970)
Installation of Dionex Ferrule Fittings (Document No. 034213)

•

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1-5

DX-120 Operator’s Manual

PeakNet Software User’s Guide (Document No. 0349 14)

•

Installing the PeakNet System (Document No. 034941)

•

1-6

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2 • Description

2.1 Operating Features

Figures 2-1 and 2-2 illustrate the main operating features of the
DX-120.

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Figure 2-1. DX-120 Operating Features (Exterior)

2-1

DX-120 Operator’s Manual

2-2

Figure 2-2. DX-120 Operating Features (Interior)

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2.1 .1 Front Control Panel

The control panel liquid crystal d isplay (LCD) shows status
information and alarm conditions. Press a button in the group
labeled DISPLAY to determine the type of status information
shown. The remaining buttons control DX-120 operation.

Figure 2-3. DX-120 Control Panel

2 • Description

Button Function

DISPLAY

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Displays the pump flow rate setting (0.5 to 4.5 mL/min).

Displays the pump pressure transducer reading (0 to

27.6 MPa or 0 to 4000 psi)

NOTE
MPa is the default pressure unit. For psi, set DIP
SW1-4 on. See Section B.10 for details.

Displays the total conductivity reading (0 to 999.9 µS).

Displays the offset conductivity reading (-999.9 to

999.9 µS). Offset conductivity is the total conductivity
minus the offset for the current run (see the description of
the Auto Offset button).

Table 2-1. Control Panel Button Functions

2-3

DX-120 Operator’s Manual

Button Function

RECORDER

Delivers a chart mark signal to the analog output. The mark
is 10% of the full-scale voltage.

Delivers a 100% signal to the analog output. Pressing the
button continuously keeps the output signal at full scale. The
default full-scale voltage is 1 V, but can be changed to 10 V
(SW4-4).

Reduces th e analog output si gnal to zero. Pres sing the
button continuously keeps the output signal at zero.

COMPONENT ON/OFF

Turns the gas pressure to the eluent reservoirs on and off.
When on, the LED on the button is illuminated. This button
is

disabled

Local/Remote below).
Turns the pump flow on and o ff. When on, the LED on the

button is illuminated. This button functions in Local or
Remote mode.

Turns the SRS power on and off, as well as the DS4
Detection Stabilizer, if installed. When on, the LED on the
button is illuminated. In the dual-column configuration, this
button controls the power to the SRS and DS4 of the
selected column set (see Section 2.2.1). This button is

disabled

Local/Remote below).

when the DX-120 is in Remote mode (see

when the DX-120 is in Remote mode (see

2-4

SYSTEM CONTROL

Toggles between Local and Remote control modes. Local is
control from the DX-120 control panel and Remote is
control from a PeakNet workstation via the DX-LAN. The
selected mode is shown in the lower right-hand corner of the
display.

A red LED on the left side of the button indicates an alarm
condition. The top line of the display in dicates the source of
the alarm: cabinet or cell leak, high or low pressure, or SRS.
Pressing the button clears the alarm. If the alarm condition
is still present, the alarm reappears after 15 seconds.

Table 2-1. Control Panel Button Functions (continued)

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Button Function

Offsets the background conductivity. After start-up, allow
the system to equilibrate. The display shows the background
conductivity (the eluent conductivity before sam ple
injection). Press Auto Offset to offset this background
reading and zero the chromatogram baseline.

Switches the injection valve between the Load and Inject
positions. The current position is shown in the lower
left-hand co rner of the dis play.

When switched from Load to Injec t, the DX-120 also:

- sends a chart mark signal to the analog output (SW4-7)

- performs an auto offset (SW3 -3)

- sends a TTL signal indicating that an injection has
occurred

After 1 minute, the valve automatically returns to the Load
position (SW1-1).

This button is
mode.

COLUMN SELECTION

The COLUMN SELECTION buttons are active in the
dual-column configuration only.

In column select mode, this button initiates the column
switching sequence from column set B to column set A (see
Section 2.2.1). In eluent select mode, this button switches to
eluent delivery from line A (see Section 2.2. 2).

In column select mode, this button initiates the column
switching sequence from column set A to column set B (see
Section 2.2.1). In eluent select mode, this button switches to
eluent delivery from line B (see Section 2.2.2).

disabled

2 • Description

when the DX-120 is in Remote

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These buttons are
mode.

disabled

when the DX-120 is in Remote

Table 2-1. Control Panel Button Functions (continued)

2-5

DX-120 Operator’s Manual

2.1.2 Pump

The pump is located on the rig ht side of the main
compartment (see Figure 2-2). The knob o n the front of the
pump adjusts the flow rate from 0.5 to 4.5 mL/min.

Eluent Save Mode

If the DX-120 is idle (i.e., no control panel buttons have been
pressed and no PeakNet commands have been received) for
90 minutes, the pump flow automatically decreases to 1/20 th
of its cur rent flow rate and the SRS cycles on and off. When
this occurs, the LEDs on the
Press any button to return to the last selected flow rate.

To turn off this feature, reset the Pump Time-out DIP switch
(SW1-2).

2.1 .3 Configuration DIP Switches

Pump

and

SRS

buttons flash.

The DIP switches on the left side of the main compartment
control system parameters. The factory-set defaults can be
changed to meet specific system and application requirements
(see Section B.10).

NOTE
In this manual, when a function is controlled by a DIP
switch setting, the switch and position numbers are shown
in parentheses. For example: (SW1-3, 4) indicates DIP
switch 1, positions 3 and 4.

2-6

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2.1.4 Eluent Reservoirs

Dionex strongly recommends degassing all elue nts and
storing them in reservoirs pressurized with helium. This helps
prevent bubbles (resulting from eluent outgassing) from
forming in the pump head and the detector cell. Degassed
eluents and pressu rized reservoirs are especially impo rtant
when combining aqueo us and non-aqueous components (e. g.,
water and methanol). With non-aqueous components, glass
reservoirs are recommended.

The single-column DX-120 in cludes one 2-liter plastic
reservoir (P/N 0441 29). The dual-colu mn DX-120 includes
two 2-liter plastic reservoirs.

The following additional reservoirs are available from Dionex:

•

1-liter plastic reservoir (P/N 044128)

•

1-liter glass reservoir with shatterproof plastic coating
(P/N 044126)

2 • Description

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•

2-liter glass reservoir with shatterproof plastic coating
(P/N 044127)

The 2-liter plastic reservoir is not designed for vacuum
degassing. Do not use it for this purpose.

2-7

DX-120 Operator’s Manual

2.1 .5 Component Panel

Chromatography components are mounted on the inside fron t
door. Figure 2-4 shows the single-column component panel
layout. Figure 2-5 shows the dual-column layout.

The DX-120 is equipped with a Rheodyne injection valve
(see Section 2.1.6). The following additional components
must be ordered separately:

•

Self-Regenerating Suppressor(s) (SRS): The SRS
neutralizes the eluent and enha nces analyte conductivity.
For a dual-column system, order two suppressors.

•

Column(s): One or two analytical columns and one or two
guard columns can be installed on colu mn clips. The clips
have larger clasps on one side for supporting 4 mm
columns and smaller clasps on the other side for 2 mm
columns.

•

Column switching valve: The column switching valve is
installed only in a dual-column system. Th e valve controls
liquid flow to the selected column (in column select
mode) or from the selected eluent (in eluent sele ct mode).
See Section 2.2 for details abou t dual-column systems.

2-8

•

Detector cell: Only one flow-through cell is required in
either the single- or the dual-column system. Two cell
models are available: a DX-120 standard cell (the
CDM-3) and a DX-120 high-performance cell with heater
(the DS4 Detection Stabilizer). The DS4 is recommended
for applications requiring enhanced thermal stability. See
sections 2.1.7 and 2.1.8 for details about the cells and the
DS4.

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SRS

2 • Description

CDM-3 Cell

Injec tion Va lv e

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Guard Column

Analytical Colum n

Figure 2-4. Single-Column Component Panel Layout

NOTE
A DS4 Detection Stabilizer can be installed instead of the CDM-3
cell.

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DX-120 Operator’s Manual

2-10

Figure 2-5. Dual-Column Component Panel Layout

NOTE
A CDM-3 cell can be installed instead of the DS4 Detection
Stabilizer.

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2.1 .6 Rheodyne Injection Va lve

The Rheodyne injection valve has two operating positions:
Load and Inject. In the Load position, sample is loaded into
the sample loop, where it is held until injection. In the Inject
position, sample is swept to the column for analysis. Eluent
flows through one of two paths, depending on the valve
position:

•

In the Load position, eluent flows from the pump, through
the valve, and to the column, bypassing the sample loo p.
Sample flows from the syringe or autosampler line,
through the valve, and into the sample loop; excess
sample flows out to waste.

•

In the Inject position, eluent flows from the pump,
through the sample loop, and on to the column, carrying
the contents of the sample loop with it.

2 • Description

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Figure 2-6. Rheodyne Injection Valve Flow Schematics

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DX-120 Operator’s Manual

2.1.7 Detector Cells

The DX-120 accommodates two detector cell models. The
DX-120 standard cell (CDM-3; P/N 050776) is used for
applications that do not require th e enhanced baseline
stability gained through thermal stabilization. For increased
thermal stabilization in high-sensitivity applications, use a
DX-120 high-performance cell with heater (DS4 Detection
Stabilizer; P/N 050218).

If you change the cell model, the Cell Type DIP switches
(SW4-1, 2) must be reset to sel ect the new cell type.

Detector Cell Features

•

Both cells are flow-through conductivity cells with
polymeric bodies. Two 316 stainless steel electrodes are
permanently sealed into the cell bodies.

NOTE

•

A sensor (thermistor) located slightly downstream from
the electrodes senses the temperature of the liquid as it
exits the cell. The measured value is used for temperature
compensation.

•

The active volume is nominally 1.25 µL for the CDM-3
cell and 1.0 µL for the DX -120 high-perfo rmance cell.

•

The detector cell constant for both cells has a nominal
value of 160 cm

-1

.

The advanced geometry of the cells provide several benefits:

•

Excellent accuracy and linearity over a broad working
range

•

Efficient sweepout and low volume for low dispersion

•

Reduced sensitivity to electrode surface conditions

•

Low electrode mass

•

Effective temperature comp ensation

2-12

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2 • Description

Temperature Control and Compensation

Temperature directly affects the conductivity of a solution.
For example, laboratory heating and air conditioning systems
can cause a regular slow cycling in the baseline. This, in turn ,
can affect the reproducibility of an analysis. The higher the
conductivity, the more pronounced the effect.

In ion chromatography, suppressing eluent conductivity
minimizes the effect of temperature variation. Temperature
compensation further improves baseline stability. When the
conductivity cell is housed in a DS4 Detection Stabilizer, the
heater enhances the ability of these techniques to reduce
temperature effects on conductivity.

Temperature compensation also ensures that there is no major
change in the baseline or peak heights, should it be necessary
to change the DS4 operating set point. Readings will be
normalized to 25 °C.

2.1.8 DS4 Detection Stabilizer

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The DS4 is a temperature-controlled chamber consisting of a
cast aluminum base and cover enclosed in insulating foam.
The chamber houses both the cond uctivity cell and the eluent
heat exchanger. Figure 2-7 identifies the major components of
the DS4.

The DS4 provides the following benefits:

•

Conductivity measurements nearly impervious to
laboratory temperature variation

•

Very low disp ersion in the eluent heat exchan ger

•

Excellent peak height reproducibility

•

User-selected temperature set point

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DX-120 Operator’s Manual

2-14

Figure 2-7. DS4 Detection Stabilizer Features

Power input to a pair of transistors on opposite sid es of the
DS4 heats it to a user-selected temperature from 30 °C to
45 °C (SW3-4, 5, 6, 7). A sensor near the heat exchang er
outlet senses the eluent temperature. The DX-120 circuitry
compares this temperature with the selected temperature and
adjusts the heat input in real time to hold the temperature
within a few millidegrees.

The DS4 is sealed with an O-ring to trap eluent that may leak
from the cell. If 5 mL of liquid accumulates, a thermistor
sensor signals a leak to the CPU. Any additional leakage will
be discharged via the spill/overflow line. A second thermistor,
above the discharge level, acts as a temperature reference for
the leak sensor.

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2.2 Dual-Column Configuration Features

The dual-column configuration has two operating modes:

Column select mode allows switching of flow from one column

•

set to the other.
Eluent select mode allows switching of flow from one eluent to

•

the other (the column set is not switched).

The Column Select DIP switch (SW3-1) selects the mode:
on=column; off=eluent.

The dual-column system option adds the f ollowing features:

2 • Description

Column A

The

•

and

Column B

buttons on the front contro l panel

are enabled .
An eluent selection valve selects which eluent reservoir is used.

•

A column switching valve directs flow to the selected column set

•

(column select mode only).

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DX-120 Operator’s Manual

2.2 .1 Column Select Mode

In column select mode, you can switc h the flow path from
one column set to the other by pressing

B

or by sending a command from PeakNet.

Figure 2-8 illustrates the sequence of events when you switch
from column set A to column set B.

Column A

or

Column

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Figure 2-8. Column Selection Sequence

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