AUTOMATIC-DETERMINATION OF INDOMETHACIN IN HUMAN PLASMA USING LIQUID-SOLID EXTRACTION ON DISPOSABLE CARTRIDGES IN COMBINATION WITH HPLC

A sensitive and automatic method for the analysis of indomethacin in plasma has been developed using liquid-solid extraction (LSE) on disposable extraction cartridges (DECs) coupled to high-performance liquid chromatography (HPLC). The fully automated system handles the plasma samples by performing the same operations as in a manuel procedure by means of an autosampler equipped with a robotic arm at which is attached a needle dispensing the different liquids. The DEC is first conditioned with methanol and phosphate buffer pH 7.4. A 1.0-mL volume of plasma is then applied onto the DEC; the latter is washed with the same buffer before the elution with 0.25 mL of methanol. The eluting strength of the eluate is reduced by dispensing 0.30 mL of phosphate buffer pH 7.4 in the collection tube prior to the injection onto the HPLC column via a 0.1-ml loop. The chromatographic separation is performed on an octadecylsilica column with a mixture of methanol and phosphate buffer pH 7.4 as mobile phase (60:40, v/v) and indomethacin is monitored photometrically at 254 nm. The effect of the plasma dispensing flow rate on the drug recovery and the importance of the guard column for the stability of the analytical column have been studied. The absolute recovery of the drug is 96.0 % and the limit of detection, 2 ng/mL. At the concentration of 100 ng/mL, relative standard deviations of 1.5 % (within-day) and 2.3 % (between-day) have been obtained.