Survey of bottled waters for perchlorate by electrospray ionization mass spectrometry (ESI-MS) and ion chromatography (IC)

Perchlorate has been identified in ground and surface waters around the USA including some that serve as supplies for drinking water. Because perchlor ate salts are used as solid oxidants in rockets and ordnance, water contami nation may occur near military or aerospace installations or defense indust ry manufacturing facilities. This ion has been added to the Environmental P rotection Agency's Contaminant Candidate List and the Unregulated Contamina nt Monitoring Rule. Concern over perchlorate has prompted many residents in affected areas to switch to bottled water; however, bottled waters have no t previously been examined for perchlorate contamination. Should the EPA pr omulgate a regulation for municipal water systems, US law requires the Food and Drug Administration to take action on bottled water. Methods will ther efore be required to determine perchlorate concentrations not only in tap w ater, but also in bottled waters. Ion chromatography (IC) is the primary te chnique used for its analysis in drinking water, but it does not provide a unique identification. Confirmation by electrospray ionization mass spectro metry (ESI-MS) can serve in this capacity. The ESI-MS method can be applied to these products, but it requires an understanding of matrix effects, esp ecially of high ionic strength that can suppress electrospray. When using m ethyl isobutyl ketone (MIBK) as the extraction solvent, the ESI-MS method c an reach lower limits of detection of 6 ng ml(-1) for some bottled waters. However, dilution required to negate ionic strength effects in mineral wate rs can raise this by a factor of 10 or more, depending on the sample. Decyl trimethylammonium cation (added as the bromide salt) is used to produce an ion pair that is extracted into MIBK. After extraction, the sum of the peak areas of the ions C10H21NMe3(Br)(ClO4)(-) (m/z = 380) and C10H21NMe3(ClO4) (2)(-) (m/z = 400) is used to quantitate perchlorate. Standard additions ar e used to account for most of the matrix effects. In this work, eight domes tic brands and eight imported brands of bottled water were comparatively an alyzed by the two techniques. For comparison, a finished potable water know n to contain perchlorate was also tested. None of the bottled waters were f ound to contain any perchlorate within the lower limit of detection for the IC method. Recoveries on spiked samples subjected to the IC method were gr eater than or equal to 98%. Published in 2000 for SCI by John Wiley & Sons, Ltd.