Development and multi-laboratory verification of US EPA method 538 for the analysis of drinking water contaminants by direct aqueous injection-LC/MS/MS

A drinking water method for 11 chemicals, predominantly pesticides, is presented that addresses the occurrence monitoring needs of the U. S. Environmental Protection Agency (EPA) for a future Unregulated Contaminant Monitoring Regulation (UCMR). The method employs direct aqueous injection liquid chromatography/tandem mass spectrometry (DAI-LC/MS/MS). The method uses sodium omadine and ammonium acetate to preserve the drinking water samples for up to 14 days. Mean recoveries of tap water samples fortified with the method analytes at 0.99-4.0 mu g L(-1) (quinoline = 43 mu g L(-1)) are 89.3-106% with relative standard deviations of less than 8%. Single laboratory lowest concentration minimum reporting levels of 0.011-1.5 mu g L(-1) are demonstrated with this methodology. Multi-laboratory data are presented that demonstrate method ruggedness and transferability. The final method meets all of the EPA UCMR survey requirements for sample collection and storage, precision, accuracy, and sensitivity. The final method is expected to be proposed for use under a future UCMR.