High accuracy method for isotope dilution mass spectrometry with application to the measurement of carbon dioxide

A new approach to the quantitative analysis by isotope dilution mass spectrometry (IDMS) has been developed that overcomes many of the limitations of established methods. It incorporates additional dilution steps that act as an internal calibration so that an independent isotopic reference material is not required. It avoids the need to measure the isotope ratio of the highly enriched spike directly, and enables the final results to be arranged as a combination of measurements that are largely insensitive to instrumental bias and drift. Consequently, it has the potential to extend the scope of application of IDMS to include analyses for which reference materials with certified isotope ratios are not available or where contamination of the instrument by the highly-enriched spike causes difficulty. The new method has been demonstrated by measuring the mass ratio of an isotopically-enriched sample of carbon dioxide in a natural sample of carbon dioxide with a relative uncertainty of 0.02%. Crown Copyright (C) 2002 Published by Elsevier Science B.V. All rights reserved.