Thermal degradation observed with different injection techniques: Quantitative estimation by the use of thermolabile carbamate pesticides

Abstract

Abstract An experiment has been designed to study the thermal degradation of thermolabile compounds caused by various injection techniques. The four carbamate pesticides aminocarb, bendiocarb, carbaryl, and dioxacarb decompose thermally into methylisocyanate and the corresponding phenol. The carbamets and the phenols arising from them were separated on a 25 m SE‐54 fused silica column; all compounds exhibited sharp peak shape indicating that the degradation observed took place completely within the injector. When cold on‐column injection was employed no thermal degradation was observed whereas with hot splitless injection at 220°C decomposition of the carbamates was almost complete. PTV injection was found to produce intermediate results. When packed with glass wool and operated with glass wool and operated with starting temperatures lower than the boiling point of the solvent, decomposition was found to be almost complete. Applying isothermal conditions at 140°C (30°C above the boiling point of toluene) aminocarb and bendiocarb underwent only slight decomposition while carbaryl and dioxacarb were about half degraded. Results from PTV injection with an empty insert resembled those obtained using cold on‐column injection and in this mode the application of temperatures up to 200°C resulted in no visible degradation. This can be explained by the short residence time of the sample in the injector.