Effect of variations in gas chromatographic-conditions on the linear retention indices of selected chemical warfare agents

Abstract Temperature-programmed gas chromatographic retention indices, relative to n -alkane and n -alkylbis(trifluoromethyl)phosphine sulphide (M-standard) homologous series, were determined for nine chemical warfare agents using SE-54 fused-silica capillary columns. The influence of changes in the chromatographic conditions on the absolute values and on the reproducibility of the indices was evaluated. Nineteen parameters were investigated, with the purpose of discovering those most critical for the retention index monitoring of chemical warfare agents. The parameters most affecting the absolute value of the indices were the carrier gas flow-rate, the temperature programming rate and the properties of the column. Changes in conditions most strongly affected the indices of the low-volatility compounds O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate (VX) and dibenz[ b , f ]-1,4-oxazepin (CR). The reproducibility of the indices was good in every case, even when the absolute values of the indices changed. Retention index monitoring is thus a reliable method for preliminary identification of compounds in mixtures, provided that the chromatographic system is regularly tested with a test mixture and corrections to the chromatographic conditions or the retention index library data are made where necessary.