Quantitative determination of methoxsalen in human serum, suction blister fluid and epidermis by gas chromatography mass spectrometry.

A selected ion-monitoring gas chromatographic mass spectrometric method is described for the determination of methoxsalen employing trioxsalen as internal standard. Methoxsalen in the serum and skin of 5 psoriatic patients after PUVA bath therapy was determined. Quantitative gas chromatographic mass spectrometric analysis was performed in the election impact mode by monitoring the ratio of ions m/z 216/228. The methoxsalen level in human serum varied between 3-15 ng/ml, in suction blister fluid between 2-9 ng/ml and in suction blister roof (epidermis) between 6-242 ng/g during the first 30 min after the methoxsalen bath.