Quantitative determination of 8-methoxypsoralene in mild dosage form by high-performance liquid chromatography

   Objectives. To develop and validate a method for the quantitative determination of 8-methoxypsoralen in a soft dosage form in accordance with the requirements of the State Pharmacopoeia of the Russian Federation, 15^th edition, and the Pharmacopoeia of the Eurasian Economic Union.

   Methods. Quantitative determination of 8-methoxypsoralen was performed by high-performance liquid chromatography on a Chromaster 5000 (Hitachi, Japan) with a diode array detector. Chromatography was performed on a Kromasil EternityXT-5-C18, 5 μm, 250 × 4.6 mm column in isocratic mode with a mobile phase of acetonitrile/water in a ratio of 50 : 50 % (v/v). The flow rate was 1.0 mL/min, while the detection wavelength was 250 nm.

   Results. The optimal condition for the extraction of 8-methoxypsoralen was found to be ultrasonic gel extraction at 40 °C for 15 min using acetonitrile. The best peak resolution of 8-methoxypsoralen was achieved during gel analysis at 250 nm using a reversed-phase sorbent with an octadecyl phase (C₁₈) grafted onto silica gel. The acetonitrile/water mixture was used as a mobile phase in a volume ratio of 50 : 50 % to minimize chromatography time while maintaining optimal resolution. From the validation procedures, it was confirmed that the method is specific, linear (R² > 0.997) and reproducible (relative standard deviation was ≤ 3.0 %). The accuracy of the analytical method was from 98.26 % to 101.02%, while the values of the detection and quantitative determination limits were 0.006 and 0.020 μg/mL, respectively. The developed quantitative determination method demonstrated its stability when varying as the column temperature and flow rate by ±5 %.

   Conclusions. As effectively implemented using the high-performance liquid chromatography method, the method for quantitative determination of 8-methoxypsoralen has a number of advantages over the previously described methods, including reduced analysis time, as well as increased sensitivity and effectiveness, which makes it possible to apply the developed method in assessing the quantitative content of 8-methoxypsoralen in a soft dosage form—gel for the treatment of psoriasis.

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