The reduction of selected redox indicator dyes during fast atom bombardment mass spectrometry was investigated in several different matrices. Reduction is indicated by the incorporation of one or more hydrogens into the cation of the dye. The extent of reduction of the analyte can be related to the E 1/2 value of the reduction potential of the dye. Selection of matrix also influences the reduction, the reducing power decreasing in the order glycerol greater than sulfolane greater than thioglycerol greater than hydroxyethyl disulfide greater than nitrobenzyl alcohol. Evidence is given suggesting that reduction is initiated by exposure of the analyte-matrix mixture to atom bombardment. It is shown that reduction can be controlled by the addition of metal ions with a very low reduction potential to the matrix to act as electron scavengers.
