Reduced-pressure microwave-induced plasma mass spectrometric detection of phosphorus and sulphur in gas chromatographic eluates

The determination of phosphorus and sulphur at trace levels is not possible by conventional atmospheric pressure plasma mass spectrometry because of high background signals at m/z= 31 (14N16OH+) and m/z= 32 (16O2+). The reduced-pressure plasmas decrease the background at the major isotopes of phosphorus and sulphur such that sub-nanogram detection is possible. The use of reduced-pressure helium and nitrogen microwave-induced plasmas for the determination of phosphorus and sulphur is discussed. With a helium plasma, the detection limit for phosphorus in triethyl phosphite ranges from 1 to 90 ng depending on the amount of torch cooling. Using a nitrogen plasma, sub-nanogram detection limits for phosphorus and sulphur in two organophosphorus pesticides were obtained.