**2.1. Ion chromatography process [4]**

Tswett's initial experiments involved direct visual detection and did not require a means of quantitation. Nowadays, chromatography is not only a separation technique. In most versions, it is hyphenated analytical techniques combining the separation with the identification and quantitative determination of the separated components. In this form, chromatography has become the most widely used technique in the chemical analysis of

**Figure 1.** Schematic diagram of the principles of chromatography as discovered by Tswett (1901).

Many versions of chromatography are used. The various chromatographic techniques are subdivided according to the physical state of these two phases, the mobile and the stationary phases. These are: liquid chromatography including high performance, ion, micellar, electrokinetic, thin-layer, gel-permeation, and countercurrent versions; gas chromatography and supercritical fluid chromatography. Various forms of chromatogra‐ phy can be used to separate a wide variety of compounds, from single elements to large molecular complexes. By altering the qualities of the stationary phase and/or the mobile phase, it is possible to separate compounds based on various physiochemical characteris‐ tics. Among these characteristics are size, polarity, ionic strength, and affinity to other compounds. Chromatography also permits a great flexibility in the technique itself. The flow of the mobile phase might be controlled by gravity, pressure, capillary action and electro-osmosis; the separation may be carried out over a wide temperature range and sample size can vary from a few atoms to many kilograms. Also, the shape of the system in which the separation takes place can be varied, using columns of various length and diameter or flat plates. Through all this, evaluation chromatography has been trans‐ formed from an essentially batch technique into an automated instrumental method. Through its continuous growth, chromatography became the most widely used analytical separation technique in chemistry and biochemistry. Thus, it is not exaggeration to call it

complex mixtures.

2 Column Chromatography

the technique of the 20th Century.

The basic process of chromatography using ion exchange can be represented in 5 steps (as‐ suming a sample contains two analytes A & B): eluent loading, sample injection, separation of sample, elution of analyte A, and elution of analyte B, shown and explained below. Elu‐ tion is the process where the compound of interest is moved through the column. This hap‐ pens because the eluent, the solution used as the solvent in chromatography, is constantly pumped through the column. The representative schemes below are for an anion exchange process. (Eluent ion = , Ion A= , Ion B = )

**Step 1**: The eluent loaded onto the column displaces any anions bonded to the resin and saturates the resin surface with the eluent anion.

This process of the eluent ion (E- ) displacing an anion (X- ) bonded to the resin can be expressed by the following chemical interaction:

Resin<sup>+</sup> -X- + E- <=> Resin<sup>+</sup> -E- + X-

**Step 2**: A sample containing anion A and anion B are injected onto the column. This sample could contain many different ions, but for simplicity this example uses just two different ions as analytes in the sample.

**Step 3**: After the sample has been injected, the continued addition of eluent causes a flow through the column. As the sample elutes (or moves through the column), anion A and anion B adhere to the column surface differently. The sample zones move through the column as eluent gradually displaces the analytes.

**Step 4:** As the eluent continues to be added, the anion A moves through the column in a band and ultimately is eluted first.

**Figure 2.** Schematic representation of IC process.

**Figure 3.** Schematic representation of Ion chromatography instrumentation.

recorder or data system as represented in Figure 4.

variety of compounds [5].

**3. Instrumentation [6-9]**

A typical ion chromatography consists of several components as shown in Figure 3. The eluent is delivered to the system using a high-pressure pump. The sample is introduced then flows through the guard and into the analytical ion-exchange columns where the ion-exchange separation occurs. After separation, the suppressor reduces the conductivity of the eluent and increases the conductivity of the analytes so they are delivered to the detector. A computer and software are used to control the system, acquire and process the data. Since the introduc‐ tion of ion chromatography in 1975, many developments were carried out to improve sup‐ pressor technology to provide better sensitivity and consistency for the analysis of a wide

Ion Exchange Chromatography - An Overview

http://dx.doi.org/10.5772/55652

5

Typical IC instrumentation includes: pump, injector, column, suppressor, detector and

This process can be represented by the chemical interaction showing the displacement of the bound anion (A¯) by the eluent anion (E¯).

Resin+ -A¯ + E¯ <=> Resin+ - E¯ + A¯

**Step 5:** The eluent displaces anion B, and anion B is eluted off the column.

Resin+ -B- + E- <=> Resin+ -E- + B-

The overall 5 step process can be represented pictorially as shown in Figure 2:

**Figure 2.** Schematic representation of IC process.

**Step 3**: After the sample has been injected, the continued addition of eluent causes a flow through the column. As the sample elutes (or moves through the column), anion A and anion B adhere to the column surface differently. The sample zones move through the column as

**Step 4:** As the eluent continues to be added, the anion A moves through the column in a band

This process can be represented by the chemical interaction showing the displacement of the

eluent gradually displaces the analytes.

bound anion (A¯) by the eluent anion (E¯).



**Step 5:** The eluent displaces anion B, and anion B is eluted off the column.

The overall 5 step process can be represented pictorially as shown in Figure 2:


+ E- <=> Resin+

Resin+

Resin+ -B-

and ultimately is eluted first.

4 Column Chromatography

A typical ion chromatography consists of several components as shown in Figure 3. The eluent is delivered to the system using a high-pressure pump. The sample is introduced then flows through the guard and into the analytical ion-exchange columns where the ion-exchange separation occurs. After separation, the suppressor reduces the conductivity of the eluent and increases the conductivity of the analytes so they are delivered to the detector. A computer and software are used to control the system, acquire and process the data. Since the introduc‐ tion of ion chromatography in 1975, many developments were carried out to improve sup‐ pressor technology to provide better sensitivity and consistency for the analysis of a wide variety of compounds [5].

**Figure 3.** Schematic representation of Ion chromatography instrumentation.
