Key parameters for carbamate stability in dilute aqueous-organic solution

Within the framework of the determination of pesticides of the carbamate fa mily, the isocyanates prove to be excellent derivatizing agents of the hydr olysis products of pesticide residues. The optimum conditions for derivatiz ation require the use of an aqueous organic solution (water-acetonitrile) w ith the presence of triethylamine. Under these conditions, the derivatives formed (ureas or carbamates) must be stable to enable a reliable and repres entative determination. Our objective, therefore, was to study the paramete rs, such as solvent, structure of the derivatizing agent, pH, nature of the catalyst, and the optimum conditions needed for stability. The kinetic and statistical analysis of 24 compounds (an analysis of variance based on 142 measurements) demonstrate that neither the effects of pH, nor of the group introduced by the derivatizing agent make it possible to simultaneously st abilize all of the formed derivatives. To ensure reliable and repeatable de termination of the carbamate (obtained after derivatization), it is necessa ry to expulse the carbamate, in the organic phase, by adding NaCl to the aq ueous-organic medium. (C) 2001 Elsevier Science Ltd. All rights reserved.