Characterisation of reference materials by isotope dilution mass spectrometry

This article reviews the application of isotope dilution mass spectrometry (IDMS) to the field of reference material (RM) characterisation within the past 15 years, focusing on elemental and elemental species analysis. Emphasis is placed on liquid and solid RMs and IDMS measurements of the highest analytical quality. Basic principles, as well as the equation system, are being revisited. Different calibration strategies, such as single, double or triple IDMS, are critically reviewed and the achievable uncertainties are discussed. Differences in the application of thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS) are discussed as well as differences between different types of mass spectrometers, such as single collector versus multi-collector or quadrupole versus magnetic sector instruments. Possible sources of errors and bias are mentioned and correction models introduced and applied within the past years are discussed. Several examples for RM characterisations and inter-laboratory comparisons for elemental as well as elemental species analysis are shown, each demonstrating excellent analytical quality. In general, it can be stated that IDMS is the most important reference method for elemental and elemental species analysis, offering the highest accuracy and precision or smallest measurement uncertainties, when properly applied. Thus, IDMS represents by far the best suited reference method for RM characterisation. Owing to its universal applicability IDMS offers sufficient potential to follow future needs in analytical chemistry as well as in the RM sector.