Solid-phase microextraction-liquid chromatography (SPME-LC) determination of lamotrigine simultaneously with carbamazepine and carbamazepine 10,11-epoxide in human plasma

A simple and specific analytical method is presented for the determination of lamotrigine (LTG) simultaneously with carbamazepine (CBZ) and carbamazepine 10,11-Epoxide (CBZ-E) in human plasma by off-line solid-phase microextraction–liquid chromatography. The best analytical conditions for the SPME procedure were established by direct extraction on a 50 μm CarbowaxTM/TPR-100-coated fiber, employing 1.0 mL of sample plasma matrix modified with 30% NaCl and with 3 mL potassium phosphate buffer (pH 9.0); extraction at 22°C; stirring at a rate of 2500 rpm for 20 min; and then desorption of the drugs by exposure of the fiber to 50 μL of the mobile phase for 10 min. The method showed good linearity (0.05 to 10.0 μg mL–1 for LTG, 0.2 to 20.0 μg mL–1 for CBZ, and 1.0 to 20.0 μg mL–1 for CBZ-E), with regression coefficients ranging from 0.9947 to 0.9978 and coefficients of variation of the points of the calibration curve lower than 10%. The limit of quantification (LOQ) for the investigated drugs in plasma varied from 0.05 to 1.0 μg mL–1.