ANALYSIS OF AROMATIC PESTICIDES BY MASS-SPECTROMETRY - ADVANTAGE OF PLASMA DESORPTION OVER ELECTRON-IMPACT AND NH3 OR CH4 POSITIVE CHEMICAL-IONIZATION - THE COMPETITIVE FORMATION OF M+ AND MH+ IONS

Electron impact (EI) using ionizing electrons of different kinetic ene rgies, ammonia and methane positive chemical ionization (PCI) and plas ma desorption (PD) mass spectrometry were used for the analysis of ary l pesticides of the carbamate and phenylurea families, Under PD condit ions, competitive formation and decomposition of M+. and MH+ ions was observed. It is shown that PD spectra give more information than do EI or PCI spectra, confirming PD as a method of choice for the analysis of small polyfunctional molecules. Rules are given for the identificat ion of these families of pesticides. A thermochemical desorption ioniz ation model defines the conditions required for the observation of bot h M+ and MH+ ions. (C) 1997 by John Wiley & Sons, Ltd.