Speciation of arsenic in urine using high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

Abstract

High-performance liquid chromatography (HPLC) has been coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of four arsenic compounds commonly found in urine. Arsenite (As³⁺), arsenate (As⁵⁺), dimethylarsinate (DMA) and monomethylarsonate (MMA) were separated via anion-exchange HPLC and detected on-line using ICP-MS. The absolute detection limits ranged from 20 to 91 pg of arsenic in aqueous media and 36–96 pg in urine. The four species were determined in two freeze-dried urine standards using the method of standard additions. The total of the four species was found to be within 13% of the average reported total arsenic concentration for both freeze-dried urine standards containing elevated levels of As⁵⁺. The relative standard deviation of peak-height measurements was less than 10% for each of the four species in urine. The determination of As³⁺ is complicated by the presence of an interfering peak, which is believed to arise from the co-elution of chlorine-containing species and subsequent formation of ⁴⁰Ar³⁵CI⁺ ions (m/z= 75).