Comparison of mass bias correction models for the examination of isotopic composition of mercury using sector field ICP-MS

Abstract

Six mass bias correction models, viz., linear law, power law, exponential law, Russell equation, common analyte internal standardization (CAIS) and polynomial function, were evaluated for the measurement of the isotopic composition of a natural abundance mercury standard solution using a sector field ICP-MS instrument. Thallium, Os and Ir were tested as internal standards. Significant differences in resultant isotope abundances were noted when the various mass bias correction models and different internal standards were used for instrument mass bias correction. The isotopic abundances calculated from Hg ratios corrected for mass bias using a polynomial function with Os, Ir and Tl as internal standards resulted in data having the smallest relative difference (Df) from IUPAC values, which were selected as common reference points. No significant Df in results arose when the power law, exponential law and Russell equation models for mass bias correction were used in conjunction with the Tl internal standard, these exhibiting the next smallest Df values. Hg isotope abundances having the third smallest Df values arose with a linear law model. Of the three internal standards examined, use of Tl for mass bias correction provided the smallest Df values with these four models, which only require one pair of isotopes from a reference standard. The CAIS model produced the largest Df values in this study.