ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY OF METALLOPORPHYRINS

The magnesium, nickel, copper, zinc and vanadium metalloporphyrins fro m octaethylporphyrin, etioporphyrin I and tetraphenylporphyrin were ch aracterized using electrospray ionization mass spectrometry (ESI-IMS). The ion abundance of each of the porphyrins present in binary mixture s was monitored as a function of the porphyrin concentration and is de pendent on the metalloporphyrin oxidation potential. It was found that , for binary mixtures of metalloporphyrins whose oxidation potentials differ by less than 0.1 V, the resulting ion abundance of each species is directly proportional to the concentration of each analyte in the mixture. For binary mixtures whose oxidation potentials differ by more than 0.1 V, relative abundances of the radical cations of each metall oporphyrin are determined by the oxidation potential and concentration of each metalloporphyrin with the analyte of lowest oxidation potenti al being ionized preferentially. Tine ability to ionize selectively on e porphyrin over another in a binary mixture offers the potential to u se ESI-MS for the qualitative analysis of porphyrins present in comple x mixtures. (C) 1998 John Wiley & Sons, Ltd.