Universal isotope dilution analysis of arsenic with labelled methane gas by dynamic reaction cell ICP–MS
An universal isotope dilution analysis method, which is applicable to determination of monoisotopic elements as well as multiple stable isotopes. The universal isotope dilution analysis for As was demonstrated using the mixture of CH4 and CD4 gases as a reaction gas in ICP–MS. When As ions react with the CH4 gas in the ICP–MS reaction cell, As+CH2 molecular ion is 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 ratio of m/z 89 and 91 is 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 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.