A GC-MS Method for Analysis of 8-Methoxypsoralen During New Immunomodulatory Therapy by Photopheresis

Malakova, Jana; Zak, Pavel; Jokesova, Iveta; Zivny, Pavel; Blazek, Martin; Zavrelova, Alzbeta; Palicka, Vladimir

A GC-MS Method for Analysis of 8-Methoxypsoralen During New Immunomodulatory Therapy by Photopheresis

2009

A new capillary gas chromatographic-mass spectrometric method has been established for analysis of 8-methoxypsoralen (8-MOP) for optimization of drug dose. The sample-preparation procedure was based on liquid-liquid extraction of 0.5 mL of an alkaline sample (leukocyte-enriched blood) with diisopropyl ether. The organic solvent was evaporated, and a methanolic solution of the residue was injected for GC-MS analysis. Ions of m/z 216 (for 8-MOP) and m/z 173 (for the internal standard 5-methoxypsoralen; 5-MOP) were recorded for data evaluation. Validation confirmed that the performance of the new method was suitable for therapeutic monitoring of 8-MOP. The limit of detection was 0.41 ng mL⁻¹. The range of applicability and linearity was from 2.5 (lower limit of quantification) to 500 ng mL⁻¹ (upper limit of quantification). Accuracy and precision were acceptable; mean recovery was from 87.2 to 104.8% and RSD was from 1.9 to 10.3%. The method was used to monitor the dose of 8-MOP during photopheresis for prevention of allograft rejection in patients with bone marrow transplantation, thus enabling modification of the dose if necessary.

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