Anion and cation determination by ion chromatography (IC)

Ion chromatography is a form of liquid chromatography, in which ion exchange resins are employed to separate atomic and molecular ions for analysis.

It is a powerful technique for determining low concentration of ions, down to the sub ppm level.

How does it work?

IC involves the retention of analyte molecules from the sample being retained based on ionic interactions. The method starts with the introduction of a sample into a sample loop of known volume.

An aqueous solution (the mobile phase) carries the sample from the loop onto a column containing a stationary phase, typically a resin or gel matrix that contains charged groups.

The target analytes are separated by virtue of their relative interaction with the mobile and stationary phases. Ions eluting from the column are detected by a conductance detector.

Sample preparation

For anion and cation analysis by IC, the analytes must be in an aqueous solution. Thus this technique lends itself to the determination of ions in water samples (drinking, waste, environmental), for which only filtration of the sample is required to ensure no particles will be injected into the system.

For solid phase extraction of particulate matter samples, ions are extracted into the aqueous phase by sonication in water. In some cases a small amount (<1%) of wetting substance, such as propan-2-ol, is used to impure the extraction of the ions.

What ions can we analyse for?

We have the capability to analyse for a large range of anions and cations. The table shows a selection of some of the more common anions and cations we analyse for.

Fluoride F-Lithium Li+
Chloride Cl-Sodium Na+
Bromide Br-Potassium K+
Iodide I-Magnesium Mg2+
Nitrate NO3-Calcium Ca2+
Phosphate PO43-Strontium Sr2
Sulphate SO42-Ammonium NH4+
Chlorite ClO2-Positive Amides
Chlorate ClO3- 
Bromate BrO3-