Semi‐Microbore HPLC for the Determination of Baclofen in Human Plasma Using Column Switching

Abstract

Using a column switching technique, a semi‐microbore high performance liquid chromatographic (HPLC) method was developed for the determination of baclofen in human plasma. Methoxamine was used as an internal standard. Following precipitation of the plasma sample with zinc sulfate–acetonitrile, the samples were directly injected onto the system. The analyte was retained in an enrichment column while endogenous plasma components were eluted out to waste. Baclofen was then back‐flushed to a semi‐micro C18 analytical column for separation and quantification with a UV detector at 220 nm. The eluents for pretreatment and separation were 20 mM potassium phosphate (pH 2.0) and 20 mM potassium phosphate (pH 3.6)–methanol (82:18, v/v), respectively. The retention time of baclofen was about 20.8 min. The mean recovery was 98.5% and the calibration curves were linear in the investigated concentration ranges of 25–800 ng/mL (r 2 = 0.9993). The detection limit of baclofen was less than 5 ng/mL. The inter‐ and intra‐day reproducibility (RSD, %) is less than 12%, even at the limit of quantification (LOQ) of the method. This analytical method showed good sensitivity and reproducibility. This method could be successfully applied to evaluate the pharmacokinetics of baclofen in healthy volunteers after the oral dose of 25 mg baclofen.