IDENTIFICATION OF CARBAMATES BY PARTICLE-BEAM MASS-SPECTROMETRY

The possibility of analysing 33 carbamate pesticides and 14 of their t ransformation products was investigated utilizing flow injection parti cle beam/mass spectrometry (PBMS) with electron impact (EI) ionization and ammonia and methane positive and negative chemical ionization (CI ). Optimum operating conditions of the interface and mass spectrometer in each mode were determined, with special attention given to spectru m quality; variables investigated included ion source temperature and ion source pressure in CI experiments. Ammonia, as a reagent gas, prov ided less fragmentation and better quantitative results than methane. The CI response was generally higher with positive ion detection (PCI) than with negative ion detection (NCI), but NCI was found to be highl y selective for compounds such as aminocarb, asulam and thiophanate-me thyl, As regards analyte detectability, EI performed best for most com pounds, with the spectra providing relevant structure information. The response of more polar degradation products is generally larger by 2- 3 orders of magnitude compared with the parent compounds. When analysi ng real samples, the combined use of CI for molecular mass determinati on and EI for structure elucidation is required. The spectral informat ion from this study and additional chromatographic data were used for the determination of low- and sub-mu g l(-1) levels of the test carbam ates in surface water.