Determination of porphyrin carbon isotopic composition using gas chromatography–isotope ratio monitoring mass spectrometry

Carbon isotopic compositions of aetio I occurring in the form of free-base, nickel, demetallation, dihydroxysilicon(IV) and bis(tert.-butyldimethylsiloxy)silicon(IV) [(tBDMSO)2Si(IV)] have shown that it has experienced no obvious isotope fractionation during the synthesis of [(tBDMSO)2Si(IV)] porphyrin from aetio I. Here, aetio I porphyrin species such as free-base, nickel, demetallated and dihydroxysilicon were analyzed by the conventional method, namely it is combusted in sealed system, and followed by isotope ratio monitoring mass spectrometric analysis. [(tBDMSO)2Si(IV)] aetio I was assayed by gas chromatography–isotope ratio monitoring mass spectrometry (GC–IRMS). A porphyrin mixture of [(tBDMSO)2Si(IV)] aetio I and octaethylporphyrin was also prepared. Their carbon isotopic compositions measured by GC–IRMS indicate that no isotope exchange took place between the porphyrins during the synthesis of [(tBDMSO)2Si(IV)] porphyrins. This method is employed for δ13C determination of geoporphyrins from the Maoming and Jianghan oil shales.