Analysis of petroporphyrins by chemical ionisation mass spectrometry
The CH4 chemical ionisation (c.i.) mass spectra of three standard porphyrins and two petroporphyrin mixtures have been examined and compared with their respective electron impact (e.i.) mass spectra. In the e.i. mode (M– 15)+ fragments are observed, the isotope peaks of which coincide with homologue molecular ions. Much reduced fragmentation is observed in the c.i. mass spectra, resulting in an easier analysis of complex mixtures of petroporphyrins. This occurs with only a slight loss in sensitivity compared with low voltage e.i. or field desorption (f.d.) mass spectrometry.