The CHROMacademy Essential Guide - On Demand webcast Introduction to Ion Chromatography
The Essential Guide from LCGC’s CHROMacademy present an educational webcast on the fundamental
principles of ion chromatography. In this session, Dr. Ken Cook (Bio - Separations Manager, Dionex)
and Tony Taylor (Technical Director, Crawford Scientific), present a definitive guide to the fundamental theory
and instrumentation of ion chromatography.
This guide considers the underlying theory of the technique, column and eluent selection and key separation variables as well as the various techniques used for ion suppression and detection. We also consider various applications of ion chromatography together with recent advances in the technique including capillary ion chromatography, fast and ultra high pressure ion chromatography as well as hyphenation of ion chromatography to mass spectrometric detectors.
A must see for everyone using or considering ion chromatography.
Dr. Ken Cook
EU Separations Science Support Manager
Dionex / ThermoFisher, UK
Basic theory of ion chromatography
Separation and detection
The ion chromatography system
Post column suppression
Eluent preparation strategies
Column choice and basic applications of ion chromatography
Eluents for ion chromatography
Altering elution times and selectivity
Advances ion chromatography
Fast ion chromatography
Capillary ion chromatography
Hyphenating ion chromatography to mass spectrometry
Ion chromatography is a generic term that applies to any method for chromatographic separation of ionic or ionisable species in solution.
The term ion chromatography (IC) encompasses a range of different techniques; however, the most important forms of IC are based on each of the following four separation mechanisms: 
Although some of the above mechanisms (like ion-suppression) do not involve traditional ‘ion exchange’ separation mechanisms, they are still considered forms of ion chromatography and are critical concepts within many ion chromatographic separations.
Based on ionic interactions between analyte ions and polar functional groups in the stationary phase, ion exchange chromatography is the most widely used of all forms of ion chromatography
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IC - Ion Chromatography
NPC - Normal Phase Chromatography
IPC - Ion Pair Chromatography
RPC - Reversed Phase Chromatography
« Figure 1:
Applicability of selected forms of liquid chromatography
Nowadays the vast majority of ion chromatographic separations are dominated by ion exchange mechanisms using stationary phases with charged functional groups. These types of mechanisms dominate the separation of analytes that permanently hold electrostatic charges (i.e. weak or strong acidic/basic species or inorganic ions).
Figure 2:Species typically analysed with suppressed conductivity detection Ion Chromatography (IC)
Ion-exchange chromatography (IEC) is based on the different affinities of the analyte ions for oppositely charged ionic functional groups in the stationary phase or adsorbed counter ions.[2, 3]
Nowadays the vast majority of ion chromatographic separations are dominated by ion exchange mechanisms using stationary phases with charged functional groups. These mechanisms dominate the separation of analytes that hold electrostatic charges (i.e. weak and strong acidic/basic species or inorganic ions) and are used in a wide variety of applications as indicated in Figure 3.
Environmental Testing Labs
Wastewater treatment facilities
Food producers and processors
Figure 3:Example of industry / application area in which ion chromatography is used
Ion-exchange chromatography (IEC) is based on the different affinities of the analyte ions for the oppositely charged ionic functional groups in the stationary phase or adsorbed counterions.[2, 3] When analysing inorganic ions this form of chromatography is often generically referred to as Ion Chromatography.
Depending on the charge of the exchange centres on the surface, the resin could be either an anion-exchanger (positive ionic functional groups on the surface) or cation-exchanger (negative functional groups on the surface). The process for the retention and separation of both anionic and cationic species are shown in Figure 4, a) and b).
Figure 4a:Anion exchange chromatography in which the stationary phase is a strongly cationic resin / polymer and analyte (chloride ion, Cl-) retention is controlled by altering the ionic strength of the eluent species, typically using the anionic counter ions shown, which are listed by counter ion ‘strength’
Figure 4b:Cation exchange chromatography, undertaken using a anionic polymer surface and using cationic counter ions as shown to selectively elute the analyte (sodium, Na+)
In ion-exchange chromatography, retention is based on the affinity of different analyte and counter ions for the charged site on the stationary phase surface and on a number of other solution parameters such as counter ion type (strength) and concentration.
Figure 5: Variables affecting retention in ion chromatography as exemplified by the separation of anions of various ‘size’ (hydrodynamic volume) and charge
In general, the elution (eluotropic) strength of the mobile phase is controlled via the nature of the counter ion chosen (some counter ions are more surface active than others and therefore displace analytes ions more readily) and the concentration of the counter ion (displacement by the law of mass action).
The selectivity in ion exchange chromatography is mainly based on differences in the material of column construction and the functional groups bonded to the polymer surface (stationary phase).
The main mechanisms for controlling retention and selectivity are shown in Figure 6.
Altering Selectivity in Ion Chromatography
Figure 6: Principle variables for altering retention
and selectivity in ion chromatography
Consider the exchange of two ions and between the solution and exchange resin R-:[1, 6]
The equilibrium constant for this process is:
K essentially determines the relative affinity of both cations to the exchange centres on the surface. If the constant is equal to one, then no discriminating ability is expected for the system.
Similarly, the exchange of two ions C- and D- between the solution and exchange resin E+ :
Depending on the charge state of the exchange functional groups on the surface, the resin could be either anion-exchanger (positive ionic functional groups on the surface) or cation-exchanger (negative functional groups on the surface).
In general terms, the ion exchange chromatographic process can consist of four main steps.
Step 1. Equilibration of the stationary phase to the desired conditions:
When the equilibrium is reached all functional groups in the stationary phase are associated with exchangeable counterions. See below:
Important pointers to consider:
In the case of anion exchangers, the exchangeable counter-ions would be of anionic nature (such hydroxide, carbonate, borate etc)
In the case of cation exchangers, the exchangeable counter-ions would be of cationic nature (H+ from HCl, methanesulfonic acid, tartaric acid etc)
Animation 2.Stationary phase equilibration on a cation exchange column (oversimplified).
Step 2. Sample application and wash:
The objective is to bind analytes to the stationary phase while washing out unwanted constituents. See below:
Where: is the Analyte of interest
Note that in many applications the optimum separation may be achieved by choosing conditions so that major and troublesome contaminants are bound to the exchanger while the substance of interest are eluted during the washing step. This procedure is sometimes referred to as “starting state elution”.
Animation 3.Sample application and stationary phase
wash on a cation exchange column (oversimplified).
Step 3. Elution of retained analytes from the column:
This step is accomplished by a change in the buffer composition, usually increasing the ionic strength of the mobile phase would be enough to elute all retained analytes. See below:
Where: is the Analyte of interest
The highest ionic strength which permits binding of the analytes of interest and the lowest ionic strength that causes their elution should normally be used as the starting and final ionic strengths in subsequent analysis. A higher ionic strength buffer is frequently used as a washing step before column regeneration.
Step 4. Column Regeneration:
All molecules that still remain bounded to the stationary phase must be removed to restore the full capacity of the stationary phase. This step is usually accomplished by changing the eluent system or buffer composition. See below:
In general terms there are only a few additions to a traditional HPLC system in order to achieve ion exchange chromatographic separations; primarily because the critical elements required for a good chromatographic separation remain the same (good mass transfer, low dead volume, suitable mobile and stationary phases).
As in traditional HPLC, ion chromatography pumping systems use reciprocating pumps which cope with the pressure and volumetric needs of most ion chromatography applications. As many of the eluent systems used in ion chromatography can be corrosive, ion chromatographs tend to be constructed from, or have hydraulic pathways which are constructed from polymer materials (PEEK, polyether ether ketone is typical)
Figure 7: » Typical reciprocating pump design with polymer components and/or hydraulic pathways used for corrosive eluent systems in ion chromatography
Columns packed with suitable packing materials have been developed to provide good separation performance in minimum time. The working life of the column can be increased by using a filtering system (guard column or in-line filter) between the autosampler and the column.
The electrical conductivity detector is one of the most important detection types for ion chromatography. It actually measures the conductivity of the mobile phase and therefore it is not a solute property detector but a bulk property detector. The principles and working principles of detectors for ion chromatography will be given in another chapter.
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Figure 8:Schematic diagram of an Ion Exchange Chromatograph (Courtesy of Dionex, a Thermo Fisher Company)
Perhaps the most noteworthy differences between a standard HPLC system anda modern Ion Chromatograph are the Eluent Generator and Electrolytic Eluent Suppressor. These components will be dealt with in greater detail in subsequent sections.
The quality of the eluent system is of overriding importance to ion chromatography, especially the level of potentially interfering background ions, as one might expect. Solutions should be freshly prepared with high quality water and additives. Please bear in mind that eluent systems for ion chromatography should always be.
Microfiltered: use 0.45 μm filter
Degassed: use helium or vacuum
Continuously stirred: use magnetic stirrers
Freshly prepared: ideally on a daily base
Prepared at the correct standard: use high quality water and chemicals
It is highly advisable to use carbon dioxide absorbers, especially when dealing with either alkaline or low buffering capacity eluent systems.
In order to avoid CO2 absorption, eluent reservoirs must be well closed with a head pressure of Helium. Remember that carbonate absorption onto low concentration OH eluents can lead to drifting problems early in the gradient.
Note that precipitation should always be avoided; this is of particular importance when changing eluent system. Solutions used in succession should be miscible. If the system has to be rinsed with an organic solution, then use solvents with increasing or decreasing lipophilic character (e.g. chloroform ↔ acetone ↔ water).
In ion chromatography, the required initial buffer concentration will vary depending on the nature of the buffering species (i.e. buffer ion ‘strength’).
Relative affinities of counter ion for the stationary phase versus the analyte ion will vary depending upon the ion-exchanger type and the analytical conditions. However it is possible to give an approximate ‘relative’ series in terms of counter ions, although modern resins are often designed to operate with simple H+ and OH- counter ion gradients.
As a rule, an increase of the charge-density (charge to solvated ion ratio) of the solute ion will increase retention due to increased coulombic interactions as the analyte and surface charges move closer together. This trend becomes more pronounced in more diluted mobile phases.
The order of affinities of commonly available cations relative to strong acid cation exchange stationary phases are generally in the following order:
Ba2+ > Ca2+ > Mg2+ > Cs+ > K+ > NH4+ > Na+ > H+
Cation-exchange mobile phases of 0.1 M KCl are stronger then those containing 0.1M NaCl, provided that all other parameters are identical.
And similarly the relative affinity of anions can be approximated as: citrate> salicylate> ClO4 > S2O32- > HPO42- > NO3- > Br- > NO2- > CN- > Cl- > HCO3- > H2PO4- > CH3COO- > HCOO- > BrO3- > ClO3- > F- > OH-
Higher degrees of cross linking result in ion-exclusion effects, i.e., exclusion of ions with higher solvated radii from the stationary phases pores. Since these ions are also less retained, they elute more quickly than ions with a smaller hydrodynamic radius, which can enter the small pores. More highly charged ions and small radius are polarizable are therefore retained longer. The effects of the last two properties in difficult to predict, making the relative series above tentative, rather than absolute.
Eluent Generation / Re-generation
Most modern instruments are equipped with eluent re-generation or generation devices which function to either re-generate the eluent system post detection OR generate simple (H+ and OH-) eluent systems ‘in-situ’, which significantly improve the ‘convenience’ of the system and serve to reduce operator error. There are many different strategies to generate high quality IC eluent systems and therefore, it would be unpractical to try to cover all of them.[11, 12]
In Figure 9, after the conductivity cell, the eluent system is recycled as a source of water for the electrolytic suppressor. Note that there is an ion trap column between the conductivity cell and the suppressor to guarantee that analyte and impurity ions will not reach the electrolytic suppressor. A fraction of the eluent system exiting the electrolytic suppressor is degassed prior to regeneration (an appropriate eluent purification column should be used) and collection into the eluent reservoir. See below.[13, 14]
Figure 9:IC system with eluent recycle (Courtesy of Dionex, a ThermoFisher company)
Figure 10:IC system with eluent generation (Courtesy of Dionex, a ThermoFisher company)
Eluent generation systems based on resins are currently used in many modern IC systems. In essence, two separate chambers form part of an electrochemical cell [15, 16]
Water is oxidized to form H+ ions and oxygen at the anode:
These protons interact with a resin and displace K+ ions from its surface:
Water is reduced to form OH- ions and hydrogen at the cathode:
As a consequence, a flow of KOH is produced. Figure 11 below illustrates the working principle of this device.
Figure 11:IC eluent generation device (Courtesy of Dionex, a ThermoFisher company)
Note that other designs are available.
Figure 12 below shows a 3D schematic view of the previous device.
Figure 12:Hydroxide Eluent Generation for Anion Analysis
Figure 13:Separation andLinearity of detector response of sulfate with KOH eluents. Conditions: 10cm ID × 20 cm length (1.7 meq/g) K+ ion supply column, will generate a flow of KOH (20.0 mM) that at 1.0 mL/min will last for up to 2225 hours (considering 100% efficiency) or 1300 hours (considering 60% efficiency).
Figure 14:High-resolution anion analysis with eluent generation (conditions shown)
Figure 15: Electronically generated eluents provide highly repeatable gradients
The column stationary phase is responsible for the ion exchange separation and its properties are of primary importance for successful separations (retention and selectivity).
The lifetime of the ion chromatography column is maximized through the use of stable bonding chemistry, and optimal proprietary packing procedures.
When selecting a column for a particular separation, the chromatographer should be able to decide whether a packed, capillary, or monolithic column is needed and what the desired characteristics of the packing material should be.
As with pumps, due to the corrosive nature of the eluent system, IC columns are usually based on alternative materials (such as PEEK) rather than stainless steel.
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The separation properties of IC columns are basically determined by the functional groups bonded to the support material. Certain analytes, however, can interact with the support material. The pdf below lists selected support materials for IC columns.[1, 2, 3, 5, 6, 17 - 22]
Ion Chromatography resins have to withstand extremes of pH as the eluents can often be KOH or Methane Sulfonic acid. The most common support material is polystyrene with divinyl benzene cross links [PSDVB].
Examples of column packing morphologies are given below:
Figure 16:Particle morphologies for modern ion chromatography columns
Ion exchangers are prepared by attaching ionic functional groups to the supporting matrix. Here the functional groups are attached to a largely polar matrix and the dominant forces that control retention will be ionic and polar.
The most common functional groups in commercially available ion exchangers are sulfonic and carboxylic acids for cation exchangers and tetramethylamino functional groups for anion exchangers. .[1, 2, 3, 10, 20, 21, 22]
The total exchange capacity of an ion exchange resin (Q) is a quantitative parameter which defines the total number of chemical equivalents available for exchange per some (nominal) unit weight or unit volume of resin. The capacity may be expressed in terms of milliequivalents per gram of resin or in terms of milliequivalents per gram of resin (mmol/g or in meq/g).
The unit equivalent (eq) can be defined as the amount of substance which will either:
react with one mole of hydronium ions (H3O+) or hydroxyl (OH-) ions in an acid-base reaction
react with or supply one mole of electrons in a redox reaction
As a matter of fact, the ion exchange capacity is usually expressed in meq (1000 meq = 1 eq) per gram
According to their exchange capacity, there are roughly three types of ion exchangers:
low-capacity ion exchangers: Q < 0.1 mmol/g
medium-capacity ion exchangers: 0.1 < Q < 0.2 mmol/g
high-capacity ion exchangers: Q > 0.2 mmol/g
Figure 17:Ion exchanger capacity classification
Effect of Stationary Phase Capacity
The higher the capacity, the greater the retention but the more difficult to suppress the strong eluents required for elution from the column.
Most ion exchange column have low capacity to improve detection and sensitivity
Complex samples and measurement of trace levels in the presence of high level matrix ions require higher capacities
These principles are demonstrated in Figure 18 in which a high capacity resin is required to gain enough retention in order to effectively separate a range of anions.
Suppressor systems are used to increase sensitivity of the technique by lowering the column’s effluent background conductivity before it enters the detector. As a consequence, ion suppressors may be considered integral parts of the detection system. Different approaches had been implemented to achieve such aim.
Ion suppressors are designed to lower the ionic strength of the column’s effluent, allowing the use of conductivity detectors.
There are two ways of ion suppression
Discontinuous (regenerating devices)
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Columns containing strongly acidic cation exchange resins have been used to decrease conductivity background in anion exchange chromatography.
The principle of column ion suppression relies on the use of weakly dissociating species in the eluent system. Let’s consider an eluent system that contains the strongly conducting sodium bicarbonate. In this case, conductivity can be reduced by using a strong cation exchange resin.
The weakly dissociated carbonic acid (CO2 + H2O) is formed from the strongly conducting sodium bicarbonate (NaHCO3 ). The depletion of sodium bicarbonate will be reflected in a reduction of eluent conductivity.
Inorganic salts (such as sodium chloride or sodium bromide) can undergo a similar process:
Resin - SO3H + NaCl → Resin - SO3Na + HCl
The inorganic acid (HCl) thus produced has a higher conductivity than the original salt (NaCl). The signal to be measured is the conductivity of HCl (high) against a low background conductivity.
Low column capacity and high dead volume are the major drawbacks of suppression columns. In fact, the need for periodic regeneration, has limit the use of suppression columns.
« Figure 19:Column suppression
use to reduce KOH background
signal in ionchromatography
The use of switching valves and suppression columns in parallel have been used to decrease system dead time during re-generation. Of course, this requires the addition of an extra pump to the system for the off line re-generation of the supprerssor.
« Figure 20:Dual suppression column system, allows off-line re-generation which speeds up analysis with this type of suppressor system
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Hollow Fiber Suppressors
A hollow fiber suppressor consists of a semi-permeable membrane that is wrapped around a cylindrically shaped body. While the eluent system flows through the fiber, a dilute solution (either acidic or basic) flows countercurrent to the eluent, in contact with the exterior of the fiber.
Figure 21.Sulfuric acid based hollow fiber device
In the animation below, the ionic strength of an eluent system composed of NaHCO3 is chemically reduced by using a hollow fiber suppressor that uses a dilute solution of sulfuric acid (H2SO4).
Figure 22:Continuous chemical suppression used to reduce a sodium carbonate background
Hollow fiber suppressors permit continuous IC operation; however, the effects of bandbroadening due to increased extra column volume and the relatively low capacity made their use obsolete by instrument manufacturers in favor of flat screen membrane suppressors.
With a much higher capacity and lower dead volume than any of its previous counterparts, flat membrane suppressors (also called ‘micro-membrane’ suppressors) are capable of continuous operation with minimal attention and minimum extra column volume.
In the same manner as hollow fiber suppressors, flat membrane suppressors use the principle of continuous regeneration; however, in comparison, feature a much higher exchange capacity. Strong ion exchange suppressor screens and ion exchange membranes are placed in alternating order, separated by ion-exchange membranes which allow very close contact of the eluent and regenerant flows. The basic design is shown in Figure 23 below.
The ion suppressor device shown in Figure 24, uses platinum electrodes for the hydrolysis of water to produce H+/OH- ions and semi-permeable ion exchange membranes to selectively reduce the ionic strength of the eluent system. Organic solvent may be added as a makeup flow to aid the desolvation process in the electrospray interface but this is often not required.
Post-column anion suppressors work in a similar manner to cation suppressors but with opposite charge.
Animation 7:Self regenerating continuous suppression process
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Figure 25:Electrochemical suppressionschematic
The invention of the high capacity, continuous suppression system allowed the use of higher capacity ion exchange columns and gradient elution for more difficult sample analysis and much higher resolution. The suppression of strong eluents can be regarded as part of the detection system and is strongly linked with the wide choice of columns now available for ion chromatography
The ion chromatography detection system is used to monitor the passage of the components as they emerge from the column.
As with any chromatographic technique, the detector measures some physico-chemical property of the mobile phase/analyte as it elutes from the column. The response of the detector will change due to changes in the column’s effluent.
Because electrolytic suppressors are designed to reduce ionic strength, the column’s effluent can be detected by conductivity.
The conductivity detector is by far the most commonly used of all IC detectors.
1 – 5 μg
10 – 50 ng
0.5 – 1.0 ng
50 – 500 pg
10 – 100 pg
10 – 100 pg
10 – 20 ng
Table 1:Selected detection types in ion chromatography
Direct Ion Chromatography
Direct ion chromatography refers to the form of IC where the column’s effluent is directly fed to the detector without any ion suppressive treatment.
The major challenge in this mode is to select an eluent system which does not produce a detector response in order to maintain required sensitivity.
Due to the drawbacks this is now rarely used
Indirect Ion Chromatography
Indirect ion chromatography refers to the form of IC where the column’s effluent is directly fed to the detector with a deliberate high background eluent system and the ions are detected as negative dips in the high background. The polarity of the signal is usually reversed to simulate a positive peek in the trace which analysts and chromatography management systems are more used to. The high background in this system does give noisy and unstable baselines and could only be used reliably for high levels.
Due to its high sensitivity and reduced background noise, the most common form of conductivity detection implements the use of ion suppression.
It has been reported that when using conductivity detectors, the use of ion suppression will increase sensitivity when analyzing cations; however, when dealing with anions, the use of ion suppression will decrease sensitivity. The table below summarizes selectivity experimental observations with conductivity detectors.[2, 27, 28]
With Ion Suppression
Without Ion Suppression
Table 2:Selectivity experimental results with conductivity detection
The table above lists suitable and unsuitable IC detection strategies for selected compounds.
Belonging to the electrochemical group, conductivity detectors, are by far the most widely used of all detectors for ion chromatography. Here, the conductivity of the column’s effluent is measured by a detection system consisting of two electrodes to which an alternating potential is applied. The corresponding current is proportional to the conductivity of the ionic solution in which the cell is dipped.
The conductivity detector can be used either with or without a suppressor system. The main function of the suppressor system is to reduce the high background conductivity of the column’s effluent, without suppressing or adversely affecting the signal of analyte ions.
Animation 8:Schematic and operating principle of a typical conductivity detector
Figure 26: Conductivity detection principle
The conductivity of a solution is measured by applying an alternating voltage between two electrodes in a conductivity cell.
At any instant in time, negatively charged anions migrate toward the positive electrode and positively charged cations migrate toward the negative electrode.
The measured electrical conductivity (measured in Siemens per cm) is given by:
Equivalent conductivity [S cm2 mol-1]
Equivalent concentration of the electrolyte [equivalents/1000cm3]
As can be seen from the previous expression, the electrical conductivity is proportional to the electrolyte concentration; this linear relationship can be expected only for dilute solutions. However, the linear association between and is adversely affect by the following factors:
The equivalent conductivity ( ) is dependent upon electrolyte concentration
The electrical conductivity ( ) is dependent upon temperature and solvent polarity
The sensitivity of the conductivity measurement depends upon the difference between equivalent conductivities of analyte (subscript a) and eluent ions (subscript e):
Relation of Conductivities
Table 3.Relation between equivalent conductivities of analyte and eluent ions and resulting peaks
The dependence between electrical conductivity and temperature is sometimes, very important. As a consequence, temperature control should be implemented (ideally, constancy should be kept within 0.01 oC of target temperature). This is particularly important if suppression is not used as the background conductance will then be high and so variable to temperature changes.
Figure 27:Conductivity detection calibration curves for nitrate determination with and without suppression
In cases where chemical suppression is used, curved calibration functions can be found and is dependent on the eluent and suppression system used (see the figure above). In such cases, it is recommended that calibration concentrations as close as possible to the concentration of the sample, (although modern data systems are able to model non-linear calibration functions). This approach will render the most accurate results. OH eluent systems especially those generated electrochemically reduce the background signal to bellow 1µs. This results in an essentially linear calibration curve for most analytes. With carbonate eluent systems the background signal following suppression can be between 10 to 30 µs depending on the concentration used. This can result in curved or quadratic calibration curves.
IC-MS is a hyphenated technique, which combines the separating power of ion chromatography with the detection advantages of mass spectrometry.
Ion chromatography has been hyphenated to a range of detection techniques including mass spectrometry and atomic absorption. The coupling of IC to these techniques can be accomplished with the implementation of post-column ion suppressors.
Note that MS renders more confidence in analyte identity than other IC detection types; this is because, IC-MS not only provides the analyte’s retention time but also it’s mass to charge ratio. This confidence could be even enhanced by the use of tandem MS techniques. Mass spectrometry detection can help to address situations where:
Specific compound identification is required
Very low limits of detection are required
Post-column ion suppression provides the means to effectively reduce the high ionic strength of IC eluents to make them compatible with MS systems.
The conductivity of the ion suppressor’s effluent is constantly monitored and is kept below certain value (usually 1.0 μS cm-1) before infusion into the MS detector. To achieve this OH based eluent systems are used with eluent generation systems and electronic suppression to give high purity eluents and the lowest ion conductance delivered to the MS system.
These systems are particularly important in cellular metabolism studies as a significant number of analytes in central metabolism are charged or highly polar. This gives them poor retention on reverse phase columns but excellent chromatography characteristics on ion exchange. For many isobaric metabolic intermediates, it would be essential to have chromatographic separation in addition to mass / charge ratio to positively identify.
MS compatible Ion Exchange
Continuous Suppression IC system
Electrolytic gradient generation
isocratic deionised water used from the pump
gradient generated pre-column electrolytically
Exchange of post-column K+ with H3O+ using electronic suppressor
The figure below illustrates the coupling of ion chromatography with MS detection system. Please bear in mind that temperature control and solvent degassing are of overriding importance to ion chromatography.
There is an increasing interest in the development of capillary ion chromatography. The use of small-bore columns with reduced diameters (usually lower than 1.0 mm id) present several significant advantages including:
Small sample volumes
Lower eluent consumption
There are many situations where resolution is more than adequate to separate sample components and in such situations, it is possible to optimize column dimensions and eluent flow rates in order to decrease analysis times while maintaining sufficient resolution. Capillary ion chromatography columns provide the means for speeding up separations (usually up to four times) whilst maintaining acceptable resolution.
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Suppressor Dead Volume
EG Current (50 mM KOH)
(50 mM KOH)
(50 mM KOH)
Table 4:Typical Conventional and Capillary IC Operating Parameters
Figure 29:Separation of common anions using a capillary AS19 column
Figure 30:Fast IC inorganic capillary anion analysis at different flow rates
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Band Broadening (3hrs)
Column chemistry (4hrs)
Reverse phase (partition) chromatography (6hrs)
Ion-Pair Chromatography (3hrs)
Normal phase (absorption) chromatography (3hrs)
Gradient HPLC (3hrs)
Quantitative and Qualitative HPLC (3hrs)
FAST HPLC (4.5hrs)
Theory and Instrumentation of GC
Chromatographic Parameters (3hrs)
Band Broadening (3hrs)
Gas Supply and Pressure Control (2hrs)
Sampling Techniques (4.5hrs)
Sample Introduction (5hrs)
GC Columns (5.5hrs)
GC Temperature Programming (3hrs)
GC Detectors (2.5hrs)
Instrumentation of HPLC
Mobile Phase Considerations (3.5hrs)
Solvent Pumping Systems (4hrs)