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

We report on high precision measurements of mercury isotopes in natural samples. The natural isotopic Fig composition in cinnabar and coal was determined using different types of ICP-MS instrumentation. The performance of 4 different 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 plasma and Fig isotope ratios were corrected for mass fractionation by measuring the Tl-203/Tl-205 ratio, simultaneously introduced as a dry aerosol. The average corrected ratio of Hg-201/Hg-202 in cinnabar using MC-ICP-MS was 0.44297 +/- 0.00001 (2 SE, internal precision). This ratio differs significantly from the currently accepted IUPAC ratio for this isotope pair. Fig isotope ratios in different coal and fly ash samples were determined after the Fig in the samples was preconcentrated onto gold traps, from which the Fig was thermally desorbed into the plasma. Consequently, Hg ratios in coal were measured oil transient signals. The ratios of Fig isotopes changed slightly during the evolution of the peak, Suggesting it mass fractionation caused by the thermal desorption step. Hence, ratios were obtained from the integrated 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 similar to that from continuous signals, indicating that isotope ratio measurement on transient signals is it viable technique.