Ion Chromatography Troubleshooting Guide - Resolving IC Analysis Issues

Ion

Chromatography

Troubleshooting

Guide

Resolving IC analysis issues

Detectors

and detection

Electrolytic

suppression

Pumps, eluent

delivery, and

pressure

Electrolytic eluent

generation

Retention

Peak shape

Selectivity

Sample injection

Resolving IC analysis issues

Ion Chromatography (IC) is the premier technique for determining ionic compounds in solution.

The basic components consist of an eluent source, pump, sample injector, separating column,

suppressor, and detector. As with any lab instrumentation, your IC system should be serviced

regularly to ensure peak performance. If problems arise that are not addressed by routine

maintenance, this troubleshooting guide provides you with suggested solutions so you can

quickly resume

generating the accurate, reliable data that Thermo Scientiﬁc

™

Dionex

™

systems are known for.

Common IC Issues

(Click on number to jump to section)

Thermo Scientiﬁc

™

Dionex

™

ICS-6000 HPIC

™

system

Sample injection

Ensure injection-valve materials are compatible with eluent conditions before use. If possible, ﬁlter all standards and

samples before injection, and ensure that the sample syringe is free of bubbles before sample loading. If possible, use

suction to draw sample into loop to avoid contamination or carryover from syringe.

Symptom

Solution

No peaks Check that the injector valve is plumbed correctly and is switching correctly. If using an autosampler,

check for trapped air bubbles, check correct location of samples and wash solutions, and check

that sampling needle is reaching the sample. Check needle tip for damage and ensure needle is

aligned properly with the injection port and is not leaking. For dual systems sharing an autosampler,

check the injection valve conﬁguration and ensure the correct valve is switching.

Poor injection

precision

Ensure use of factory recommended autosampler settings and that the injection valve waste line

is routed as recommended in the manual. Check sample transfer line calibration. Check syringe

operation and replace, if necessary. As above, check the autosampler operation, and check for air

bubbles. Check and wash the rotor and seals, replacing if necessary. For manual injection, leave the

needle in the needle port while switching the valve to inject. Check the stability of the sample and

standards.

Sample carryover Check the sample and standard compatibility with eluent and for signs of sample precipitation.

Flush the injection loop with up to 10 volumes of sample before injection. For problematic (viscous)

samples, dilute further if possible.

Reduced or reducing

peak heights

Check for adsorption, precipitation, or evaporation of sample or sample components within sample

vial or connecting tubing. Carry out the above maintenance procedures to ensure correct valve

operation.

Excessive pressure and

pressure spikes during

injection

Conﬁrm that the valve is switching quickly and smoothly. Ensure that the valve and loop are free

from salt deposits and signs of precipitation. Wash (sonicate) or replace rotor, seals, and loop as

necessary.

Leaking injector May be caused by a worn or scratched injector valve rotor or a damaged injector rotor and needle

seals. Remove each, wash, check, and replace if necessary.

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Retention

In IC, analyte retention is dependent upon eluent strength and, for weak anion and cation exchangers, pH.

Variation in retention is generally the result of eluent preparation errors or pump issues.

Symptom Solution

Decreasing

retention times

Column usage can affect capacity. Reproduce the production test chromatogram using conditions

noted on the Quality Assurance Report that was shipped with the column to assess column

performance. If capacity has been lost, attempt column regeneration per the manufacturer’s

recommendations or replace the column. Check the eluent concentration. Irreversible adsorption of

highly charged species from samples will reduce available capacity. Check the sample for potential

sources of column fouling. Use IC sample preparation to minimize matrix effects and

prevent column fouling.

Increasing

retention times

Verify that the actual eluent concentration and ﬂow rate are what have been speciﬁed in the method.

For organic ions, check secondary hydrophobic interactions (switch to more hydrophilic ion

exchange column if available).

Variable

retention times

Check the eluent concentration and pump stability. Ensure that there is sufﬁcient equilibration time

between runs. Check injection volumes and concentrations of sample and standard; if the column is

being overloaded, try a higher capacity column, or inject a smaller volume. To eliminate ﬂuctuations

due to changes in room temperature, place column in thermostatted oven.

Detection and detectors

Suppressed conductivity detection is by far the most common detection mode for modern IC. Other commonly used

detectors include UV absorbance and electrochemical. For all detector types,

eluent purity and correct preparation are

key to successful IC separations.

Symptom Solution

Excessive noise Check all predetection modules (including suppressor) for sources of noise and eliminate.

Check for trapped air bubbles in detection cell. Check detection cell for any visible contamination and

clean if necessary. Check lamp usage time (UV absorbance detection), replace if necessary.

Baseline drift Check for changes or drift in ﬂow rate. Check for ﬂuctuations in room temperature. Use column

and detector cell temperature control (conductivity detection). Check for column bleed and

contamination (remove column and remeasure baseline drift). For absorbance detection, ensure

sufﬁcient warm-up and check lamp usage time.

Periodic baseline

ﬂuctuation

If ﬂuctuations appear to be synchronous with pump cycle, purge the pump and check for general

functionality. To eliminate the potential for air in the ﬂuidics, degas eluents or source water

(for eluent generation) and purge pump.

No peaks Check the injector operation. Check standard integrity. As above, ensure that all predetector

modules are operating correctly. Check the baseline noise. To verify detector operation, remove

the column and inject standard to observe response. For UV absorbance detection, ensure correct

wavelength setting.

Lack of analyte

sensitivity

Carry out a signal-to-noise analysis and compare to previous data. Verify the eluent conditions

and suppressor function (conductivity detection). Check the eluent composition and background

conductivity or absorbance (high background signal can obscure analyte peaks.) Check for proper

injector functioning.

Nonlinearity Check the system precision, both with and without column. Check the baseline and standard

stability over time. Ensure that the signal-to-noise ratio is constant. Work above 10:1 signal-to-noise

ratio for quantitation. Make sure you are not overloading the column. Establish and work within linear

range. Note: For weak acid and weak base species, conductivity is fundamentally nonlinear.

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Peak shape

Poor peak shapes are generally a sign of secondary (non-ion exchange) interactions with components within the

system, stationary phase, suppressor membranes, or adsorbed contaminants (such as metal ions). For increased

IC column lifetime, always prepare eluents from deionized water (resistance over 18 MΩ -cm) and highest purity

(manufacturer-recommended) reagents. Always use a guard column.

Symptom Solution

Tailing peaks Reproduce the production test chromatogram using conditions noted on the Quality Assurance

Report that was shipped with the column to assess column performance. Check for improper tubing

connections (use of Dionex IC PEEK Viper ﬁttings is recommended). Check if tailing occurs with

all peaks or only with certain analyte classes or individual ions (this will help identify if secondary

interactions are causing tailing). For unwanted hydrophobic interactions, use a more hydrophilic

column or use an organic solvent additive to eluent (check complete system compatibility). If metal

contamination is suspected use the manufacturer’s recommended column reconditioning procedures.

Fronting peaks Check the column capacity and avoid sample overloading. Check the eluent concentration

setting for eluent generation cartridge in Thermo Scientiﬁc

™

Chromeleon

™

Chromatography Data

System (CDS) software, or manual eluent preparation calculations and pH. Check for possible

column voiding or packing irregularities and replace the column, if necessary.

Split peaks These are most often caused by column overloading. See above advice for fronting peaks.

This may be a sign of column void, in which case the column requires replacing.

Ghost peaks Check the system for contamination. Sources can include deionized water system tubing, manually

prepared eluent reagents, and autosampler wash water. Ensure complete elution of strongly retained

ions before the next sample injection. System peaks are often seen when peaks appear because of

eluent ion retention.

Selectivity

Selectivity refers to the relative order in which retained analytes elute from a column. Considerable variety exists

in IC stationary phase chemistry, including a range of strong, weak, and mixed-mode ion exchangers based upon

nonporous, porous, and agglomerated resins (and monoliths), together with a large range of silica-based phases.

In IC, eluent pH can play a signiﬁcant role in selectivity for weakly acidic and basic ions, and affect retention and

selectivity on weak ion exchangers. Use the Virtual Column online tool available on AppsLab to ﬁnd the best

Thermo Scientiﬁc

™

Dionex

™

IC column for your analytes of interest.

Symptom Solution

Reduced resolution Check eluent concentration and pH (particularly important when using weak ion exchangers and

nonsuppressed detection modes). Verify proper pump function. Check the column temperature

stability and use a thermostatted column oven, if available. Reproduce the production test

chromatogram using conditions noted on the Quality Assurance Report that was shipped with the

column to assess column performance. Check for sample matrix effects.

Increased resolution As above. Increased retention of solitary or speciﬁc ions indicates system contamination. Apply

regeneration or washing procedures and repeat.

Changes in column-to

column selectivity

Check to see if the difference is due to lot-to-lot variation by comparing the column performance

certiﬁcates (Quality Assurance Report, QAR). Check the column usage history. Apply regeneration

or washing procedures.

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Electrolytic suppression

Always ensure that the manufacturer’s guidelines for correct hydration, startup, operation, shutdown, and storage

procedures

are followed precisely to avoid irreversible damage. If error messages are observed, consult the operation

manual before attempting a solution. Always check solvent compatibility of electrolytic modules before using organic

solvents within IC eluents.

Symptom Solution

Leaking suppressor

module

Check that connectors and tubing are correctly ﬁtted. With suppressor module off-line, check back

pressure of downstream modules and eliminate any excess pressure sources (see suppressor

manual for detailed instructions). Check inlet and outlet ﬂow for both regenerant and eluent solutions

independently to detect leaks across suppressor membranes. If breakthrough is detected, replace

suppressor.

Increasing background

and baseline noise

Check and reduce excess back pressure (ensure that the conductivity cell is operating at

recommended back pressure). Check eluent and regenerant solution purity and ﬂow. If noise

continues, carry out suppressor cleaning and regeneration procedures per the manufacturer’s

recommendations.

Baseline spiking Ensure that the correct suppressor settings are being used. Ensure the purity and gas-free condition

of all solutions. Remove traces of contamination with cleaning procedures and rehydrate the module.

Poor linearity and

deteriorating peak

shapes

For anion-exchange IC, poor peak shapes can result from metal ion contamination of the membrane.

Regeneration or cleanup of the membranes using the manufacturer’s recommended procedures

should be attempted.

Electrolytic eluent generation

Always ensure that the manufacturer’s guidelines for correct startup, operation, shutdown, and storage

procedures

are followed precisely to avoid irreversible damage. If error messages are observed, consult the operation

manual before attempting a solution. Always check solvent compatibility of electrolytic modules before using organic

solvents within IC eluents.

Symptom Solution

Leaking eluent

generator cartridge

Check and tighten the ﬁttings. Check for tubing blockages and high system back pressure. If the

cartridge itself leaks, replace cartridge.

No power Check the power supply, connections, and contacts.

Low system pressure Check cartridge and EG degasser for leaks and if present, replace. Ensure high-pressure pump

is primed.

No peaks Conﬁrm that the correct concentration has been set in the instrument method. Ensure that the eluent

concentrate cartridge has not been exhausted.

High eluent background Check the water supply purity. Ensure that the continuously regenerated trap column is replaced

each time the eluent cartridge is replaced or after one year of use. Verify proper suppressor operation.

Back to instrument image

Pumps, eluent delivery, and pressure

Typically, in ion chromatography, inert (PEEK) dual piston pumps are used. Stainless steel pumps designed for

use with HPLC, should be avoided due to incompatibility with IC eluents. Check all deionized water and eluent

reservoirs and connecting tubing for signs of contamination and particulates. Only use the highest quality sources for

preparation of eluents and ﬁlter them before use.

Symptom Solution

Fluctuating and

pulsing ﬂow

Purge the pumps with degassed eluent. Persistent bubbles in the pump heads usually can be

removed using degassed methanol or propanol. If pulsing persists, remove the check valves and

wash (sonicate in water-methanol). If the problem persists, consider replacing the seals and cleaning

the pump heads. Ensure that sufﬁcient system back pressure is provided.

Fluctuating pressure

reading

As above, carry out purging, cleaning, and maintenance procedures.

Air bubbles Filter using a 0.45 µm inert hydrophilic ﬁlter (avoid cellulose) and degas all eluents thoroughly, using

sonication under vacuum. Purge the pumps each time fresh eluent or water is prepared.

Leaking pump heads Check the seals and replace, if necessary. Check instrument manual for eluent compatibility with

pump seals.

Salt deposits Wash with water to remove (check piston for scratches and replace, if scratched). Check the piston

heads for leaks. Replace the seals if necessary.

High back pressure Ensure pump ﬂow rate is not set too high. Check for excess backpressure tubing installed between

the pump and injection valve, and remove or replace, as needed. Ensure the IC system can support

the typical operating pressure of the installed column as speciﬁed in product manuals. Check

the guard column for blocked frits and replace, if necessary. Check each module and waste line

for blockages and ensure that ﬁttings are not overtightened. Ensure tubing of the correct internal

diameter is used throughout the IC system and that there are no excessive bends.

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Instrument service support

For Dionex technical support, call 1-800-532-4752, option 2 or email

customercare.dionex@thermoﬁsher.com

Back to instrument image

Find out more at thermoﬁsher.com/IC

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