Pipette tip solid-phase extraction and gas chromatography–mass spectrometry for the determination of mequitazine in human plasma

Mequitazine has been found to be extractable from human plasma samples using MonoTip C18 tips, inside which C18-bonded monolithic silica gel was fixed. Human plasma (0.1 mL) containing mequitazine and cyproheptadine as an internal standard (IS) was mixed with 0.4 mL of distilled water and 25 μL of 1 M potassium phosphate buffer (pH 8.0). After centrifugation of the mixture, the supernatant fraction was extracted to the C18 phase of the tip by 25 repeated aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C18 phase were then eluted with methanol by five repeated aspirating/dispensing cycles. Without evaporation and reconstitution, the eluate was injected into a gas chromatograph injector and detected by a mass spectrometer with selected ion monitoring in the positive-ion electron impact mode. The separation of mequitazine and the IS from each other and from impurities was generally satisfactory using a DB-1MS capillary column (30 m × 0.32 mm i.d., film thickness 0.25 μm). The recoveries of mequitazine and the IS spiked into plasma were more than 90.0%. The regression equation for mequitazine showed excellent linearity in the range of 0.2–200 ng 0.1 mL−1, and the detection limit was 0.05 ng 0.1 mL−1of plasma. The intra-day and inter-day coefficients of variation for mequitazine in human plasma were not greater than 8.16 and 9.24%, respectively. Accuracy for the drug was in the range of 90.0–97.4%. The data obtained from determination of mequitazine in human plasma after oral administration of the drug are also presented.