Multispecies calibration: a novel application for inductively coupled plasma tandem mass spectrometry

Abstract

Inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) has significantly expanded the reach of analytical atomic spectrometry. In this work, we take advantage of the gas-phase chemistry available in ICP-MS/MS to propose a novel method of calibration. Rather than employing several standard solutions and a single mass-to-charge ratio, multispecies calibration (MSC) uses only one standard reference concentration and several chemical species of a monoisotopic element for calibration. In this work, multiple oxide and ammonia species generated in an ICP-MS/MS collision/reaction cell are used to determine As, Co and Mn in rice and liver samples. Only two calibration solutions are required per sample: S1 is a 1 : 1 mixture of sample and standard solution; S2 has the same 1 : 1 volume ratio of sample and blank. They are run separately, and the analytical calibration curve is built by plotting signal intensities from several ions containing the analyte. S1 and S2 signals are plotted on the x-axis and y-axis, respectively, and each point in the calibration plot corresponds to a different analyte species. The instrumental limits of detection calculated for As, Co and Mn were 0.07, 0.03, and 0.07 μg L⁻¹, with RSDs estimated as 7.8, 3.1 and 1.8%, respectively (n = 10). Certified and MSC-determined values of As, Co and Mn in Tomato Leaves (NIST 1573a) and Bovine Liver (NIST 1577b) presented no statistically significant differences (Student's t-test, 95% confidence level, n = 3). The MSC results were comparable and sometimes better than values determined by the traditional external standard, internal standard and standard additions calibration methods.