Measurement of high precision isotope ratios for mercury from coals using transient signals

We report on high precision measurements of mercury isotopes in natural sam ples. The natural isotopic Fig composition in cinnabar and coal was determi ned using different types of ICP-MS instrumentation. The performance of 4 d ifferent multicollector (MC) ICP-MS instruments was evaluated and compared to results obtained by collision cell ICP-MS and ICP-time-of-flight-MS. Hg in cinnabar (Almaden, Spain) was continuously introduced into the ICP plasm a and Fig isotope ratios were corrected for mass fractionation by measuring the Tl-203/Tl-205 ratio, simultaneously introduced as a dry aerosol. The a verage corrected ratio of Hg-201/Hg-202 in cinnabar using MC-ICP-MS was 0.4 4297 +/- 0.00001 (2 SE, internal precision). This ratio differs significant ly from the currently accepted IUPAC ratio for this isotope pair. Fig isoto pe ratios in different coal and fly ash samples were determined after the F ig in the samples was preconcentrated onto gold traps, from which the Fig w as thermally desorbed into the plasma. Consequently, Hg ratios in coal were measured oil transient signals. The ratios of Fig isotopes changed slightl y during the evolution of the peak, Suggesting it mass fractionation caused by the thermal desorption step. Hence, ratios were obtained from the integ rated signal or the individual isotopes for the entire sample. The external precision between replicate samples was typically ill the order of 300 to 4000 ppm (2 RSD). The external reproducibility of transient signals was sim ilar to that from continuous signals, indicating that isotope ratio measure ment on transient signals is it viable technique.