Evaluation of Laser Desorption Ionization Coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry To Study Metalloporphyrin Complexes

Abstract

In this study, the applicability of positive-ion (+) laser desorption ionization (LDI) as an ionization method for metalloporphyrin complexes was evaluated. The evaluation was performed by analyzing standard compounds and a series of crude oils with various V4+ and Ni2+ contents by (+) LDI and (+) atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The analysis of standard compounds showed that molecular ions were main ionic species in (+) LDI. Fragmented ions because of the loss of CH3 were also observed. The analysis of crude oils showed that the sensitivity of (+) LDI toward metalloporphyrin complexes is greater than that of (+) APPI. Furthermore, five types of ion VO2+ and Ni2+ porphyrin complexes (etio, DPEP, rhodo-etio, rhodo-DPEP, and di-DPEP) were observed with (+) LDI, but only three types were observed with (+) APPI. Nickel porphyrins were observed in unfractionated oils by (+) LDI but not by (+) APPI. The summed relative abundance...