Solvent and Matrix Combinations in the Quality of Matrixassisted Laser Desorption/Ionization‐Time of Flight Mass Spectra Obtained from Microorganisms

We have studied a number of commonly used matrices and a range of solvent systems, of widely varying polarity, used in matrix assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectra in an attempt to devise an optimum analytical strategy for the rapid characterization of pathogenic microorganisms. Several groups have recognized the usefulness of MALDI-TOF mass spectrometry in the characterization of these microorganisms, however, no consistent methodology has yet been developed which is in general use. Escherichia coli ATCC 9637 organisms were initially washed to remove growthmedium contaminants and then extracted with one of a range of solvents before admixing with either a single matrix ([2-(4-hydroxyphenylazo)]-benzoic acid, 2-mercaptobenzothiol, 2-amino-4-methyl-5-nitropyridine, or 2,6-dihydroxyacetophenone) or binary and ternary combinations of the four matrices. The results indicated that a binary combination of [2-(4-hydroxyphenylazo)]-benzoic acid and 2-mercaptobenzothiol (1:1) as matrix provides the most useful data with the organisms being extracted with 17% formic acid, 33% isopropyl alcohol and 50% water.