Rapid Determination of Organophosphorus Pesticides on Surfaces of Fruits and Vegetables by MS/MS with Desorption Electrospray Ionization

Desorption electrospray ionization-tandem mass spectrometry (DESI-MS/MS) was applied to the rapid determination of residual amounts of 6 organophosphorus pesticides (OPP′s), i.e., acephate, thimet, rogor, etrimfos, ethion and phosemet, on surface of fruits and vegetables, without sample preparation and pretreatment. In the MS/MS analysis, ESI was used as ion ization source with methanol as the electrospray solvent, and positive electrospray ionization as well as collision induced dissociation reaction monitoring mode was taken for qualitative and quantitative analysis. The characteristic peaks of the fragments of 6 organophosphorous pesticides with (m/z) 206, 261, 230, 293, 407, 340 respectively were confirmed. It was found that the fragmentation regularity of molecules of the 6 OPP′s were in coincidence with their molecular structures, and the possibility of arising false positiveness of the results of detection was thus eliminated. Values of detection limit (3S/N) found were in the range of 5.0×10-10-1.0×10-8g·cm-2. Precision of the method was tested with sample introduction of 1.0×10-8g·cm-2 of mixture of the 6 OPP′s for 8 determinations, values of RSD′s found were in the range of 1.6%-6.5%.