2-PHASE MATRIX-ASSISTED LASER DESORPTION IONIZATION - MATRIX SELECTION AND SAMPLE PRETREATMENT FOR COMPLEX ANIONIC ANALYTES/

Two-phase matrices, consisting of a binary mixture of solid particulat es and a low vapour pressure liquid, are shown to be effective for the production of both positive-ion and negative-ion laser desorption/ion ization mass spectra (LDI-MS). It was found that matrix selection can be guided by criteria developed previously for Past-atom bombardment m ass spectrometry. Two-phase matric-assisted (MA)LDI-MS of a variety of complex anionic analytes is presented. Sample pre-treatment using 'dr op dialysis', or exposure to an acid-activated Nafion(R) cation-exchan ge membrane, substantially enhances the quality of negative-ion mass s pectra. (C) 1997 by John Wiley & Sons, Ltd.