The assay of fentanyl and its metabolites in plasma of patients using gas chromatography with alkali flame ionisation detection and gas chromatography-mass spectrometry.

Fentanyl was determined using gas chromatography (GC) and alkali flame ionisation detection (AFID), in the plasma of patients who had received a high single dose (up to 60 microgram/kg body weight). The relative standard deviation is 6% for 11 ng/ml while the calculated detection limit is 3.3 ng of fentanyl per 1 ml of plasma. The concentration of fentanyl in patients ranged from 40 to 3 ng/ml of plasma. The concentration of fentanyl in patients ranged from 40 to 3 ng/ml of plasma in the first hour after administration. In the plasma of patients treated with fentanyl two metabolites could be detected and identified using GC-AFID and GC-MS.