Determination of amobarbital and phenobarbital in serum by gas chromatography–mass spectrometry with addition of formic acid to the solvent

A rapid and accurate method for quantification of amobarbital and phenobarbital was developed using gas chromatography–mass spectrometry (GC–MS) without derivatization. Though the compounds measured without derivatization showed low sensitivity because of adsorption, addition of 3% formic acid to the solvent improved the sensitivity for the analytes. Taking account of matrix effect, solid-phase and liquid–liquid extraction from serum were examined. The correlation coefficients of the calibration curves were 0.9995 or better, and the accuracy and precision of intraday and interday assays were in line with Food and Drug Administration (FDA) criteria.