Trace ion chromatography

Due to the increased sensitivity of instrumentation, analytical detection limits can now reach ng/L (ppt) levels on a routine basis, and even pg/L (ppq) levels under certain conditions. Confidence in the data recorded for these trace analyses relies on the control of several conditions and parameters. Besides the technical performance of instruments, careful sample handling and reagent purity are the main parameters that can be controlled.1 Water is one of the most important reagents because it is used in so many applications. Rinsing of liquid chromatography chains, dilution and preparation of blanks and samples, and final elution are just some examples where water is used. Because of this broad range of applications and the volumes required, extreme care must be taken with water quality. In particular, in trace ion analysis, constant and reproducible high purity water, free of residual ions, is necessary. Several methods are available to analyze ions with varying degrees of sensitivity: Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES), Inductively Coupled Plasma – Mass Spectrometry (ICP-MS),2,3 Flame Atomic Absorption Spectroscopy (FAAS), Electrical Atomic Absorption Spectroscopy (GFAAS)4 and Ion Chromatography (IC) combined with UV-Vis spectroscopy or electrical conductimetry.5 Ion chromatography, combined with conductivity measurement, has become a reliable and popular method for analyzing a large variety of anions and cations in dilute samples.6,7 This method has been developed in several research areas, such as the study of Antarctic ice,8 in the semi-conductor industry,9 and in analytical research domains, such as environmental analyses of air,10 soil,11 and water.12,13 The need for qualification and validation of drinking water, in order to meet new standards and regulations, has also encouraged more widespread use of IC, and the development of novel analytical techniques. There is a real challenge involved in developing a water purification system that can produce suitable water quality for trace analysis, and can monitor this water quality on demand, in compliance with Good Laboratory Practices. In this study, concentrations of the major ions detected in tap water were studied by IC at various stages of the water purification chain. Abstract : Ion chromatography (IC) has been recognized as one of the most competitive techniques for trace analysis, based on results from continuing research and development work into different types of instrumentation. Ultratrace analysis requires the use of extremely clean reagents, including water. The ionic content of water was monitored by IC along a water purification chain, from tap water to ultrapure water. Anion and cation concentrations decrease from ppm levels, in the tap feedwater, to ppt levels, in ultrapure water. This study shows that ultrapure water from a Milli-Q® system is suitable for trace analysis by IC.