A physicochemical model f o r vapor-liquid equilibrium in niulticomponent formaldehyde-containing mixtures (Maurer, 1986;Hasse et al., 1990;Hasse and Maurer, 1991a)

A new HPLC-UV method has been developed, validated and applied for the determination of isocorydine (CAS 475-67-2) in rat plasma after oral or intravenous (i. v.) administration. Caffeine was used as the internal standard (IS). The analyte and IS were extracted from rat plasma by liquid-liquid extraction (LLE) with methyl tert-butyl ether and they were separated on an XTerra C18 column (250×4.6 mm, 5 µm, pH 1-12) with UV detection at 264 nm. The mobile phase consisted of methanol and 0.02 mol/L potassium dihydrogen phosphate-phosphoric acid buffer solution (pH 3.2) (30:70, v/v) at a flow rate of 1 mL/min for 8.5 min. The retention times of isocorydine and caffeine were approximately 6.5 and 5.1 min, respectively. The good linearity of the calibration curves was observed over the concentration range of 0.05-8 µg/mL (n=8, r 2≥0.9995). The lower limit of quantification (LLOQ) was 0.05 µg/mL [signal to noise ratio (S/N)≥10], and the limit of detection (LOD) was demonstrated as 0.01 µg/mL (S/N≥3). The mean extraction recovery ranged from 83.7% to 89.5% at 3 quality control (QC) concentrations. Intra-day and inter-day precision (relative standard deviation, RSD%) were within 4.7% and accuracy (relative error, RE%) ranged from -1.2% to 4.5%. The developed method was successfully applied to determination of the pharmacokinetic properties of isocorydine in rats after oral administration at a dose of 20 mg/kg and i. v. injection at 5 mg/kg.