Universal isotope dilution analysis of arsenic with labelled methane gas by dynamic reaction cell ICP-MS†
A universal isotope dilution analysis method, which is applicable for the determination of monoisotopic elements as well as multiple stable isotopes was used. The universal isotope dilution analysis for As was demonstrated using a mixture of CH4 and CD4 gases as the reaction gas in ICP-MS. When As ions react with the CH4 gas in the ICP-MS reaction cell, As+CH2 molecular ions are selectively produced. Therefore, a mixture of CH4 and CD4 gases is introduced into a reaction cell to generate As+CH2 (m/z 89) and As+CD2 (m/z 91), and the signal intensity ratios of m/z 89 and 91 are measured with and without a third element (89Y+ or 91Zr+). The As concentration is calculated from the intensity ratios and the mass abundances of CH4, CD4, and the third element (89Y or 91Zr). The universal isotope dilution analysis was applied to the determination of As in certified reference materials, and the As concentrations determined were consistent with the certified values.