Multi-Isotope Internal Standardization for Inductively Coupled Plasma Mass Spectrometry

Recent developments in trace analyte determination have evolved from the traditional relationship relating analyte signal to concentration to “multisignal” methods where both axes are measured instrumental signals. However, many multisignal methods are limited in some fashion: Some have low sample throughput, some result in poor accuracies in difficult sample matrices, and others require several significant signals for each analyte species. Multi-isotope internal standardization (MIIS) is a newly developed calibration method for inductively coupled plasma mass spectrometry (ICP-MS) that addresses the issues presented by other multisignal techniques. Multiple isotope masses for both the analyte species and several internal standards are used to build a calibration curve. Only two solutions are required to perform the calculation. Spike recovery experiments performed in complex matrices known to be problematic for ICP-MS yielded analyte recoveries of approximately 100% with relative standard deviations on the order of a few percent. MIIS was found to outperform both traditional calibration techniques as well as other multisignal methods. MIIS was validated through the determination of a suite of analytes in three certified reference materials with recoveries ranging from 85 to 111%. MIIS provides a clear advancement over other multisignal calibration techniques developed for ICP-MS, resulting in an exceptionally high number of calibration points even though only two calibration solutions are prepared.