Microemulsion mediated in situ derivatization–extraction and gas chromatography–mass spectrometric analysis of alkylphosphonic acids

Detection and identification of environmental signatures of chemical warfare agents is an important aspect of verification program of Chemical Weapons Convention (CWC). Alkylphosphonic acids (APAs) are ultimate and persistent degradation products of nerve agents. Their identification in a sample submitted for off-site analysis infers possible indication of contamination with nerve agents. This paper describes the development of a new sample preparation method which involves ‘in situ derivatization and extraction’ (INDEX) of acids from water. Derivatization is performed by alkylation of APAs with alkylbromides in surfactant less microemulsion (SLME). The derivatized analytes were analyzed by gas chromatography coupled with mass spectrometry. The developed method involves simultaneous derivatization (alkylation) and extraction of acidic analytes mediated by surfactant less microemulsion. Various derivatization–extraction parameters such as solvent, reaction time and temperature, base and alkyl bromides were optimized. Pentyl bromide in the presence of potassium carbonate and diisopropylamine at 100 °C derivatized the selected acids efficiently. Kinetic data for alkylation of methylphosphonic acids and some carboxylic acids were obtained to assess their relative susceptibility for alkylation in microemulsion. Methylphosphonic acid and isopropyl methylphosphonic acid took 140–150 min to reach completion while carboxylic acids took 100 min to complete the reaction. INDEX could be successfully performed even in the presence of interfering Ca2+ and Mg2+ ions.