Determination of Two Antiepileptic Drugs in Urine by Homogenous Liquid-Liquid Extraction Performed in A Narrow Tube Combined with Dispersive Liquid-liquid Microextraction Followed by Gas Chromatography-flame Ionization Detection

A simple and efficient homogenous liquid-liquid extraction method performed in a narrow tube combined with dispersive liquid-liquid microextraction method has been presented for the simultaneous determination of two antiepileptic drugs in urine followed by gas chromatography with flame ionization detection. In this method, a mixture of acetonitrile and urine sample (homogenous solution) is loaded into a column partially filled with solid sodium chloride. By passing the homogenous solution through the salt layer, acetonitrile is separated from the aqueous solution as the fine droplets and collected on top of the column as a separated phase. The obtained organic phase is removed and mixed with an extraction solvent, and then the resulting mixture is rapidly injected into an alkaline solution. Various experimental parameters affecting performance of the proposed method such as type and volume of extraction solvent, pH, and flow rate in homogenous liquid-liquid extraction step, and type and volume of extraction solvent and ionic strength in dispersive liquid-liquid microextraction step were investigated. The relative standard deviation of the proposed method was <8% (n = 6, C = 1 μg L-1 of each analyte). The limits of detection for phenobarbital and carbamazepine were 0.017 and 0.010 μg L-1 and the limits of quantification were 0.056 and 0.033 μg mL-1, respectively.