APPLICATION OF MATRIX-ASSISTED-LASER-DESORPTION IONIZATION FOURIER-TRANSFORM MASS-SPECTROMETRY TO THE ANALYSIS OF PLANAR PORPHYRINS AND HIGHLY SUBSTITUTED NONPLANAR PORPHYRINS/

The applicability of matrix-assisted laser desorption/ionization (MALD I) Fourier transform mass spectrometry to the analysis of porphyrins h as been examined. High resolution spectra were readily obtained with g ood sensitivity and a detection limit as low as 2 fmol, A mixed solven t system of toluene and ethanol (1 : 1 by volume) proved to be compati ble with the 2,5-dihydroxybenzoic acid (DHB) matrix and solubilized mo st of the porphyrins examined in this study. Porphyrins which were ins oluble in this solvent mixture could be dissolved in an appropriate so lvent and deposited on a layer of DHB (layered (MALDI). The parent ion was generally the largest peal; in the spectrum, although for some me talloporphyrins the peak corresponding to (M- metal + 3H)(+) was domin ant. The extent of demetallation was found to depend on factors such a s sample preparation, the metal ion and the laser intensity, Addition of more than one hydrogen occurred in many cases but was a minor proce ss. Spectra of compounds ionized by different methods showed increasin g fragmentation in the order MALDI < layered MALDI < fast-atom bombard ment < laser desorption.