Liquid chromatography in pharmaceutical analysis X: Determination of chlorzoxazone and hydroxy metabolite in plasma

A method for the high-pressure liquid chromatographic determination of chlorzoxazone and its hydroxy metabolite in human plasma samples is presented. The separation of the compounds is achieved on an octadecylsilane column with a mobile phase of absolute methanol-distilled water (40:60) at a flow rate of 2.0 ml/min (3100 psig). The chromatographic separation is achieved within 10 min. The overall analysis time is about 45 min, which includes extraction of the drug and metabolite from plasma followed by high-pressure liquid chromatographic separation and quantification. The accuracy of the procedure is in the 1-5% range.