Thermospray mass spectrometry of diquaternary pyridinium oxime salts

Abstract

The thermospray (TSP) mass spectra of a number of diquaternary pyridinium oxime salts, used as reactivators of organophosphate-inhibited cholinesterases, were recorded without the addition of an electrolyte. The TSP mass spectra appeared to be strongly dependent on the concentration as well as on the capillary tip temperature of the interface. At low concentrations doubly charged cations were the major fragments in most of the recorded TSP mass spectra. At concentrations well above 0.001 M as well as at too high tip temperatures more complicated spectra were obtained, probably due to fragmentation and/or decomposition. These latter spectra did correspond with the published data obtained by desorption ionization methods of these compounds. TSP mass analysis without the addition of an electrolyte appeared to be rather insensitive to the oxime salts. Using full mass scanning around 1 μg of material was necessary to produce a TSP mass spectrum.