Simultaneous determination of N-methylcarbamate pesticides by LC/atmospheric pressure-ionization MS

An analytical method for the determination of N-methylcarbamate pesticides with liquid chromatography/mass spectrometry (LC/MS) has been developed. Under reversed-phase liquid-chromatographic conditions seven N-methylcarbamate pesticides have been analyzed using atmospheric-pressure chemical ionization (APCI) and electrospray ionization (ESI) methods. The effects of additives to the liquid chromatographic mobile phase, the capillary exit voltage with ESI methods and the temperature of the vaporizer with APCI methods on the sensitivity for the detection of N-methylcarbamates were examined. The sensitivities of the ESI methods were higher than those of APCI methods. Large volumes of river-water samples were directly injected into the precolumn, and then N-methylcarbamates were separated by an analytical column with a column-switching technique. The detection limits of these pesticides ranged from 20 ppt to 100 ppt. The overall recoveries of pesticides were from 92 to 101% {RSD(n = 5) were from 1.7 to 3.3%} for river water.