High-performance liquid chromatographic determination of methoxsalen in plasma after liquid—solid extraction

An improved method suitable for the determination of 8-methoxypsoralen in the range 50–1500 ng/ml in the plasma of psoriatic patients undergoing PUVA (psoralens and long-wave ultraviolet light) therapy is proposed. A 5-ml aliquot of plasma containing sodium citrate as anticoagulant was centrifuged, griseofulvin was added as internal standard and the sample was denatured with acetonitrile. The supernatant was applied to C₁₈ cartridges and 8-methoxypsoralen was eluted with methanol. The evaporated eluate was reconstituted in the mobile phase for high-performance liquid chromatography (HPLC) and applied to the HPLC column: mobile phase, acetonitrile—0.01 M phosphoric acid (34:66); flow-rate, 1 ml/min; temperature, 40°C; column, Spherisorb 5 ODS, 100 mm × 4.6 mm I.D., 5 μm particle size; UV detection at 248 nm; detection limit, 15 ng/ml of plasma.