Capillary GLC assay for carbinoxamine and hydrocodone in human serum using nitrogen-sensitive detection.

Capillary gas chromatography using an open tubular fused silica column and NP-FID was applied to the simultaneous analysis of the antihistamine, carbinoxamine, and the antitussive, hydrocodone, in human serum. Carbinoxamine and hydrocodone were extracted into methylene chloride-2-propanol (9:1) under alkaline conditions along with their respective internal standards, brompheniramine and N-ethylhydrocodone. The basic drugs were back-extracted into 0.1 N sulfuric acid and reextracted into benzene after making the aqueous phase alkaline with potassium hydroxide. The benzene extracts were evaporated to dryness and the residues were reconstituted with 40 microliter of n-nonyl alcohol-methanol (19:1). Samples (1-2 microliter) were injected onto the capillary column in the splitless mode (solvent effect) at 185 degrees and the temperature programmed to 250 degrees. Calibration curves using spiked serum standards were linear to at least 20 ng/ml for both drugs. Coefficients of variation averaged +/- 6.1% for carbinoxamine and +/- 5.0% for hydrocodone in the 2-15 ng/ml range. Sensitivity was estimated to be approximately 0.2 ng/ml for a 2-ml serum sample. Serum levels of carbinoxamine and hydrocodone were determined in a human volunteer administered these drugs.