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 (1H NMR) and those provided by GC 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 °C. An on-column injection validated as providing no degradation was used to analyse the identical solution that in 1H 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.