Use of the international system of units (SI) in isotope ratio mass spectrometry.

In this communication, we show how the established principles of the International System of Units (SI) can be used to develop a basis for stable, comparable and coherent measurements of isotope ratios by mass spectrometry. We show that there are no important differences in the traceability of quantities that represent ratios of the abundance of isotopes and those that represent fractions. However, it is important to distinguish between results expressed in 'absolute' terms and those expressed relative to stated references such as those expressed in terms of the commonly used quantity 'delta'. Copyright Crown copyright 2002