Determination of Perchlorate at Trace Levels in Drinking Water by Ion-Pair Extraction with Electrospray Ionization Mass Spectrometry

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Abstract
Perchlorate has been added to the U.S. Environmental Protection Agency's Drinking Water Contaminant Candidate List (CCL). The present work describes the analysis of perchlorate in water by liquid−liquid extraction followed by flow injection electrospray mass spectrometry (ESI/MS). Cationic surfactants, mostly alkyltrimethylammonium salts, are used to ion-pair aqueous perchlorate, forming extractable ion pairs. The cationic surfactant associates with the perchlorate ion to form a complex detectable by ESI/MS. The selectivity of the extraction and the mass spectrometric detection increases confidence in the identification of perchlorate. The method detection limit for perchlorate based on 3.14σn-1 of seven replicate injections was 100 ng L-1 (parts per trillion). Standard addition was used to quantitate perchlorate in a drinking water sample from a contaminated source, and the concentration determined agreed within experimental error with the concentration determined by ion chromatography.