Gas-phase basicities of deprotonated matrix-assisted laser desorption/ionization matrix molecules

The gas-phase basicities (GB) of eight matrix-assisted laser desorption/ionization (MALDI) matrix anions were determined using a modified bracketing method. Reference anions were generated by laser desorption from a newly developed two-phase liquid/solid mixed matrix, allowing measurements at a well defined temperature (299 K) and under low pressure conditions. The most basic matrix anion found was that of 3-aminoquinoline (GB = 1451 kJ/mol) and the least basic was the 2,4,6-trihydroxyacetophenone anion (GB = 1324 kJ/mol). Consequences for the MALDI process are discussed with respect to matrix ion formation, oligonucleotide and protein analysis. Ground-state proton transfer plume reactions between matrix anions and analyte molecules were found to be energetically favorable in many cases. (Int J Mass Spectrom 184 (1999) 25-38) (C) 1999 Elsevier Science B.V.