An improved high‐pressure liquid chromatographic assay for secobarbital in serum

A high‐pressure liquid chromatographic method for the analysis of secobarbital in serum was developed. Secobarbital was extracted from buffered serum (pH 5.5) with a solvent mix of hexane‐ether‐n‐propanol. 5‐(4‐Methylphenyl)‐5‐phenylhydantoin was added as an internal standard. Separation of secobarbital and internal standard from serum constituents and other drugs was achieved on a 5‐μm C‐18 reversed‐phase column using an acetonitrile‐phosphate buffer (pH 4.4) mobile phase. The eluent was monitored at 195 mm. The sensitivity limit of the assay was ∼0.02 μg/ml with 0.5 ml of serum sample. The application of this method to pharmacokinetic studies in pediatric patients was demonstrated.