A single-step assay for lidocaine and its major metabolite, monoethylglycinexylidide, in plasma by gas-liquid chromatography and nitrogen phosphorus detection.

A single-step extraction method for the analysis of lidocaine and its primary metabolite, monoethylglycinexylidide (MEGX), is described. Alkalinized plasma or serum is extracted with ethyl acetate. Trimecaine is used as the internal standard. One microliter of the ethyl acetate extraction solvent is injected directly onto a Carbowax-KOH column fitted to a gas chromatograph equipped with a nitrogen-phosphorus detector. This procedure provides a rapid and reliable analysis for lidocaine and MEGX, requires only a single glass tube, and eliminates back-extractions and solvent evaporation.