Investigation of LC-MS Analysis Conditions for Phenylarsenic Compounds and Its Application to Groundwater Samples at Kamisu, Ibaraki Prefecture

An analytical method for the determination of Diphenylarsinic acid (DPAA), Phenylarsonic acid (PAA) and Phenylmethylarsinic acid (PMAA) in groundwater by liquid chromatography mass spectrometry (LC/MS) has been developed. The phenylarsenic compounds were separated by LC with an anion-exchange column, and identified by electrospray ionization mass spectrometry using the m/z 261, 201, and 199 as monitoring ions for DPAA, FAA and PMAA, respectively. Quantitative measurements were performed by the internal-standard method with isotope-labeled phenylarsenic compounds as internal-standard compounds, in which quantification was not influenced by the matrix effect. The instrument quantification limits by this analytical method were 0.77 mu g L-1, 0.48 mu g L-1 and 0.30 mu g L-1 for DPAA, PAA and PMAA, respectively. We found monitored phenylarsenic compounds in groundwater by this method for two years. The occupancy of each phenylarsenic compound to the total arsenic concentration was 85 % (DPAA), 11 % (FAA) and less than 1 % (PMAA)., respectively, until the earthquake that occurred on 11th Mar 2011, but that varied after the earthquake. The cause was presumed to be due to the exchange of the pumping wells.