Chemical Isotope Dilution for 14C Ams and the Potential for GC/AMS

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Abstract
The advent of accelerator-based mass spectrometry (AMS) radiocarbon dating has reduced the minimum sample size required to ca 1 mg from the 1 g of traditional beta counting techniques (cf Wölfli, Polach & Andersen, 1984). However, it is clear that even smaller samples will be necessary for some fields of endeavor, particularly environmental work where the absolute quantities are small, perhaps of the order of a few micrograms (Currie et al, 1985). This raises serious problems in the handling and measurement of such small amounts, so that dilution will sometimes be required. Normally, sample dilution is accomplished by adding “dead” CO2 to the combusted sample CO2, which requires very careful measurement of two gas pressures for the calculation of a dilution ratio. By forming a chemical derivative of a sample before combustion, gas pressure measurement is not necessary and an exact dilution ratio can be selected by judicous choice of the dilution reagent. This paper demonstrates that such a technique is possible for the AMS 14C dating of derivatized amino acids.

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