BETA-CARBOLINE ALKALOIDS AS MATRICES FOR UV-MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY IN POSITIVE AND NEGATIVE-ION MODES - ANALYSIS OF PROTEINS OF HIGH-MOLECULAR-MASS, AND OFCYCLIC AND ACYCLIC OLIGOSACCHARIDES/

We report that commercially available beta-carbolines (nor-harmane (9H -pyrido[3,4-b]indole), harmane (1-methyl-9H-pyrido[3,4-b]indole), harm ine (7-methoxy-1-methyl-9H-pyrido[3,4-b]indole), harmol (1-methyl-9H-p yrido[3,4-b]indol-7-ol), harmine dihydro-7-methoxy-1-methyl-9H-pyrido[ 3,4-b]indole) and harmalol 3,4-dihydro-1-methyI-9H-pyrido[3,4-b]indol- 7-ol)), are useful MALDI matrices at 337 nm, for cyclic oligosaccharid es (cyclodextrins, range 972-1290 Da), acyclic oligosaccharides (range 342-828 Da) and high molecular mass proteins (range 23 290-66 525 Dal in both positive and negative modes. This was investigated by using t ime-of-flight (TOF) mass spectrometers of different sensitivities, equ ipped with and without pulse extraction facilities. A comparison with conventional matrices for carbohydrates (DHB and DHB/HIC) indicates th at beta-carbolines provide the same level of sensitivity and resolutio n in the positive mode, but offer the advantage of high levels of sens itivity and resolution in the negative mode, Harmaline has been found to be specially effective for the analysis of high-mass proteins in bo th modes, and also exhibits excellent experimental reproducibility of the results owing to the homogeneous crystallization of the analyte-ma trix mixture over the entire sample surface area, Harmane and nor-harm ane are both excellent matrices for high-mass proteins also, As MALDI matrices, beta-carbolines permit measurement of sulfated sugars in the negative ion mode as ([M-H]), and of neutral sugars and proteins as b oth [M+H](+) and [M-H](-) in appropriate modes. (C) 1998 John Wiley & Sons, Ltd.