[Solid phase extraction and high performance liquid chromatographic determination of enalapril in human plasma]

A reversed phase high performance liquid chromatographic method utilizing solid phase extraction has been described for the determination of enalapril in human plasma. The C18 sorbent cartridges were conditioned and plasma samples were applied, washed with 20 mmol.L-1 HCl (2 x 0.5 ml) and petroleum ether (boiling range 60-90 degrees C) subsequently; and eluted with methanol (3 x 0.5 ml). The eluent was evaporated to dryness, reconstituted in 100 microliters mobile phase and injected. Chromatographic separation was achieved on a Spherisorb C8 column (200 mm x 4.6 mm, 5 microns), with ethanol--water--10% H3PO4--triethylamine (30:70:1.5:0.1) at a flow rate of 1.0 ml.min-1. UV detection was set at 215 nm. The calibration ranges were 2.5-150 ng.ml-1 with regression coefficient of 0.997 and detection limit of 1.5 ng.ml-1. The within-day RSD and between-day RSD were < 8.73%, the recovery of method > 91.6%. This method was applied to the pharmacokinetic analysis of enalapril in 8 human volunteers.