In this paper we discuss recent work investigating the extent to which it is possible to move away from this ideal 1:1 blend isotope ratio whilst retaining the key benefits of the approximate matching technique. This has been used for the first time for applications where the sample has a very high analyte concentration, which would require unacceptably high amounts of spike with the existing method.
The methodology has been validated for sulfur using a well-characterised candidate matrix reference material - NIST SRM1624d. This is a diesel fuel sample that contains approximately 4000 �g g-1 sulfur. Results were obtained using a ratio for 32S/34S of 14, achieving accuracy and uncertainty comparable with the original method using a blend isotope ratio of 1.
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