Study of normalization method of isotopic compositions to isotope reference scales

In stable isotope ratio mass spectrometry (IRMS), the stable isotopic composition of samples is measured relative to the isotopic composition of a working gas. This measured isotopic composition must be converted and reported on the respective international stable isotope reference scale for the accurate interlaboratory comparison of results. This data conversion procedure, commonly called normalization. In this paper, we present a discussion and mathematical formulation of several existing routinely used normalization procedures. By utilizing laboratory analytical data, the accuracy of the various normalization methods (given by the difference between the true and the normalized isotopic composition) has been compared. Our computations suggest that single-point anchoring produces normalization errors, that it must not be used for routinely anchoring stable isotope measurement results to the appropriate international scales. Using two or more certified reference standards produces a smaller normalization error provided that the isotopic composition of the standards brackets the isotopic composition of unknown samples.