Combination of 1H nuclear magnetic resonance spectroscopy and mass spectrometry as tools for investigation of the thermolytic and solvolytic effects Case of carbamates analysis

The carbamate pesticides are a well known thermo-sensible compound class. Under unfavourable conditions, these compounds are highly prone to degradation via fragmentation and/or rearrangement mechanisms. Their transformation processes are observed in consequence of two factors: structure with fragile bonds on the one hand and a stressing environment on the other hand leading to a difficult direct gas chromatography (GC) analysis, i.e. Without derivatisation. In this paper, we investigated an original methodology based on the complementarity of analysis by proton nuclear magnetic resonance spectroscopy (H-1 NMR) and those provided by CC hyphenated with ion-trap mass selective detection (GC-ITMS) to investigate combined effects of temperature and solvent nature affecting the behaviour of 16 carbamates. Among tested solvents, toluene and acetonitrile with 0.1% acetic acid were considered as the best solvents for storage and GC analysis respectively. Carbaryl, chlorpropham, carbofuran and N-sulfenylated compounds began to be thermodegraded with a loss equal to 1-5% even at 50 degrees C. An on-column injection validated as providing no degradation was used to analyse the identical solution that in I H NMR and it was emphasised that results of the measured degradation rates were identical at +/- 2%. It was highlighted that this methodology was extensible to study mechanisms and parameters with other (bio)molecules. (C) 2009 Elsevier B.V. All rights reserved.