Study
of normalization method of isotopic compositions to isotope reference scales
Li ke,Zhang li,Zhao guoxing
Abstract
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.