has proper occurrent part isotope ratio mass spectrometry elemental analysis isotope ratio mass spectrometry EA-IR-MS Mass spectrometry where the sample is first subject to elemental analysis (dropped onto a heated reactor which contains an oxidant–-such as copper and chromium oxide–-and combusted at 900 C to produce N2, NOx, H2O and CO2 which are reduced in a stream of helium) before the relative abundance of isotopes in the sample is determined. CHMO:0000507 elemental analyser isotope ratio mass spectroscopy elemental analyser isotope ratio mass spectrometry EA-IRMS elemental analysis isotope ratio mass spectroscopy elemental analysis