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U.S. Environmental Protection Agency (EPA) Method 314 (Hautman et al. 1999) was developed as an improvement to the 1997perchlorate (ClOsub4/sub) analytical method established by the California Department of HealthServices. The minimum reporting limit (MRL) for Method 314 was set at 4 ug/L (with anMDL of 1 ug/L) and was shown to be consistently achievable, even in high TDS matrices.This MRL has been used for both the California and Federal Unregulated ContaminantMonitoring Rules (UCMR) for ClOsub4/sub. However, following the promulgation of theseregulations, both EPA and California determined that the level of interest for ClOsub4/sub could wellbe below 4 ug/L and possibly as low as 1 ug/L. In response to this increased level of interestthe authors have evaluated some of the options that have been proposed for reducing thereporting limit to sub-ug/L levels. Of particular interest were modifications to Method 314that could be performed to reduce the MRL without significantly increasing the cost of theanalysis in lieu of going to other instrumental methods. Methods based on LC-MS or IC-MShave been investigated by others as highly sensitive techniques for trace level ClOsub4/subdetermination, but would require additional instrumentation not readily available in most labs.Because of the high visibility of ClOsub4/sub as an environmental contaminant, it is critical thatmethods be able to reliably and accurately quantify ClOsub4/sub to at least 1 ug/L.Several options exist for potentially reducing ClOsub4/sub reporting limits. Because MWH Labsanalyzes in excess of 100 samples per week for ClOsub4/sub, reflecting a variety of different aqueousmatrices, it was critical to ensure that the selected methods could withstand continued use in ahigh production laboratory. Potential methods evaluated included: increasing the signal-to-noiseratio by reducing the background signal and noise through the use of various suppressors orsuppressor operating configurations, increasing the sample size without exceeding columncapacities, looking at alternative pretreatment techniques to remove interferences, andperforming on-line pre-concentration with selective "heart cutting" (Tian et al, 2003). It wasalso important to ensure that the method modifications could still meet the quality controlcriteria of Method 314, which is considered the "gold standard" for ClOsub4/sub monitoring. One waythis was done was to consistently include standards at the ppb/sub-ppb level in analytical runsunder various conditions to monitor response on an ongoing basis. This paper provides anevaluation of each approach that was tested and make recommendations for futuredevelopments. Includes 4 references, tables, figures.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 11File Size: 1 file , 360 KB