Rapid identification of Mg‐chelated chlorins by on‐line high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

On‐line high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (HPLC/APCI‐MS) has been applied to the identification of a number of tetrapyrrolic pigments as well as several magnesium‐free analogs. Mass spectra, acquired both in positive (+) and negative (−) ionization mode, allow not only the determination of the structural features of the pigments, but also a very easy differentiation of the Mg‐chelated pigments from the free bases. In the positive ionization mode, all pigments show mainly a [M + H] + ion and a [M + H − C 20 H 38 ] + fragment ion corresponding to the loss of the phytyl chain via a hydrogen rearrangement. In the negative ionization mode, on the other hand, although all pigments give an abundant molecular anion [M] −· , only the Mg‐chelated chlorin spectra show a prominent fragment [M − C 20 H 39 ] − produced by a formal loss of the phytyl radical. Copyright © 2000 John Wiley & Sons, Ltd.