Sensitive gas chromatographic quantitation of zomepirac in plasma using an electron-capture detector

A highly sensitive, specific and precise gas chromatographic method for the determination of the non-narcotic analgesic agent, zomepirac, in plasma is described. The pentafluorobenzyl ester derivative of zomepirac has been prepared. This enables the detection of zomepirac down to picogram levels using electron-capture detection. The lowest concentration of zomepirac which can be measured accurately and precisely (coefficient of variation less than 15%) is 5 ng/ml in a 2-ml plasma sample or 25 ng/ml in a 0.1-ml plasma sample. Two previously reported high-performance liquid chromatographic (HPLC) assays have detection limits of 50 ng/ml for 1-ml samples and 10 ng/ml for 2-ml samples, respectively. The present method is very useful when small sample size or interference is causing problems with the HPLC assay. This assay has been employed successfully in analyzing plasma samples from humans and monkeys as well as samples from rat milk.