Detection of water-soluble vitamins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using porphyrin matrices

The detection of water-soluble vitamins B-1, B-2, B-6, B-12 and C by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOFMS) was attempted by studying 17 porphyrin matrices. Comparative studies of porphyrin matrices, useful mass spectral window, matrix/analyte molar ratio (M/A), ultraviolet-visible absorption characteristics and quantitative results were made. Most porphyrin matrices provide a useful mass spectral window in the low-mass range. The optimal M/A increases with increasing molecular mass of the vitamin. Vitamin B-12 possesses the highest molecular mass and requires a higher M/A. The presence of hydroxyl or carboxyl groups in the porphyrin is an indicator of a useful MALDI matrix. Vitamins B-2 and B-6 were readily ionized upon irradiation with a 337 nm laser without the use of any porphyrin matrix. Improved linearity and sensitivity of the calibration curves were obtained with samples prepared with a constant M/A. The limits of detection and quantitation are at the picomole level. The results indicate that MALDI-TOFMS with porphyrin matrices is a rapid and viable technique for the detection of low molecular mass water-soluble vitamins. Copyright (C) 2002 John Wiley Sons, Ltd.