DETERMINATION OF TRACE-ELEMENTS IN WATER BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY - COLLABORATIVE STUDY

A joint U.S. Environmental Protection Agency (U.S. EPA)-AOAC interlaboratory method validation study was conducted on U.S. EPA method 200.8, Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma-Mass Spectrometry. The purpose of the study was to determine and compare the mean recovery and precision of the inductively coupled plasma-mass spectrometry (ICP-MS) analyses for 20 trace elements in reagent water, drinking water, and ground-water. The formal study was based on Youden's nonreplicate plan for collaborative tests of analytical methods. The test waters were spiked with the 20 trace elements at 6 concentration levels in the 0.8-200 mug/L range, prepared as 3 Youden pairs. Thirteen collaborators spiked 100 mL aliquots of the test waters, acidified them with 1 mL concentrated HN03 and 0.5 mL concentrated HCl, reduced the volume to 20 mL by heating in an open beaker at 85-degrees-C, refluxed them for 30 min at 95-degrees-C, and diluted them to 50 mL. After centrifuging or settling the samples, a 20 mL portion of the supernatant was diluted to 50 mL and analyzed by ICP-MS. Related experiments evaluated the method performance in wastewater and wastewater digestate at a single concentration pair, and an alternative nitric acid digestion procedure. Mean recoveries for reagent water, drinking water, and groundwater were generally 95-105% with between-laboratory relative standard deviations about 4-8%. The method also worked well with wastewaters and digestate, with between-laboratory relative standard deviations averaging 8% and recoveries averaging 100%. Recoveries of silver, however, were low in all matrixes at concentrations over 100 mug/L. The nitric acid digestion procedure was comparable in accuracy and precision to the mixed-acid digestion in U.S. EPA method 200.8. The method was adopted first action by AOAC INTERNATIONAL.