Quantitation of perchlorate ion: Practices and advances applied to the analysis of common matrices

In 1997, low-level perchlorate contamination (<50 ng mL(-1) or parts per billion) was discovered in the western U.S. Since that time, it has been found in sites scattered around the nation. Although the Environmental Protection Agency has not established a regulation for perchlorate in drinking water, it has placed perchlorate on the contaminant candidate list (CCL) and the unregulated contaminants monitoring rule (UCMR). A provisional and unenforceable concentration of 18 ng mL(-1) will stand until at least late 2000 when EPA hopes to issue a revised toxicological assessment. However, the need for techniques and methods for determining perchlorate is not constrained to environmental chemistry. Perchlorate salts are used pharmaceutically in Europe to treat Graves' disease and amiodarone-induced thyrotoxicosis. Ammonium perchlorate is used as a solid oxidant in space shuttles and intercontinental ballistic missiles. Thus, methods and techniques are necessary for quality control and quality assurance. Moreover, analysis of explosives and post-explosion residues have made quantitation of perchlorate important in forensic chemistry. A variety of techniques is available: gravimetry, spectrophotometry, electrochemistry, ion chromatography, capillary electrophoresis, mass spectrometry-each has its strengths and weaknesses. Within each technique, assorted methods are available with corresponding limits of detection. As the breadth of matrices undergoing analysis expands from potable water to agricultural runoff, fertilizers, fruit juices, or physiological and botanical fluids, the risk for interference becomes greater. As toxicologists demand lower and lower limits of detection, it falls to analytical chemists to ensure selectivity and sensitivity go hand-in-hand. In the near future, we can expect refinements in sample pretreatment and clean-up as well as analytical methods geared toward analyzing more complex matrices. Ion chromatography, capillary electrophoresis, Raman spectrometry, and electrospray ionization mass spectrometry will all play roles in environmental analysis; however, IC should be expected to dominate drinking water analysis. This review describes the state of the science and how it might be applied, and looks forward to where it is going and how it might get there.