Importance Of Pure Water In Modern Ion Chromatography

By Paul Whitehead, PhD, Chem, FRSC, Laboratory Manager, ELGA R&D Facility

Ion chromatography (IC) is evolving to meet the analytical demands for more rapid analyses using significantly smaller sample volumes. Sub-5 minute analysis times and sub-µl sample volumes are now becoming available for some applications, along with a number of improved detectors. To take full advantage of these changes it is essential that sensitivity and reproducibility are maintained. The purity of the water used has a key role to play.

Introduction
IC has seen a continuing increase in popularity over recent years due to its relative simplicity and improved reliability and utility. A form of liquid chromatography, it uses ion-exchange based stationary phase materials to separate atomic or molecular ions for qualitative or quantitative analysis. When the sample is injected onto the IC column, in the presence of eluent, sample ions are attracted to the stationary phase of the column to differing extents and are eluted sequentially by the eluent. A suppressor module is typically used to remove the eluent and sample counter-ions before the sample is detected (most commonly by conductivity). The different modes of chromatography (anion exchange, cation exchange and ion exclusion) simply relate to the different types of columns used to achieve the separation of the ions, but anion exchange chromatography forms the largest group of IC methods due mainly to the lack of alternatives methods to analyze trace levels of anions. Common applications include testing for common anions (US EPA Method 314.1, perchlorate (US EPA Method 332.0, 314.2) and haloacetic acids (US EPA Method 557) in drinking water.

Using pre-concentration techniques in which ions are initially concentrated on a small ion-exchange column prior to elution into the eluent stream, IC is capable of providing detection limits down to the ng/L scale and for a sample in a homogeneous, ionic form, very little sample preparation is required; quantified results can often be obtained within a matter of minutes. As such, the technique finds application in a diverse range of industries, from pharmaceuticals, bio-analytics and petrochemicals, to the determination of ionic contamination on the surfaces of wafers, chips and packages.