C-13 isotopic analysis of an acetaminophen and diacetylmorphine mixture

When using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) to measure the C-13 isotopic enrichment of acetaminophen, the nitrogen atom of the molecule can potentially distort the isotopic enrichment as NO2 and N2O can be formed during combustion and interfere with some of the CO2 isotopomers. Nevertheless, the comparison of isotopic enrichments obtained either by elemental analyser-isotope ratio mass spectrometry (EA-IRMS) or by GC-C-IRMS leads to the conclusion that nitrogen atoms do not interfere and that it is possible to accurately measure the C-13 enrichment of acetaminophen by GC-C-IRMS even if the combustion interface does not include a reduction furnace. Moreover it is possible to measure isotopic enrichments from samples in which acetaminophen is mixed with diacetylmorphine (heroin) even if transacetylation occurs during the gas chromatographic process. It is then necessary to acetylate acetaminophen and to take into account the constant and reproducible isotopic fractionation induced by acetylation.