High performance liquid chromatography microassay for the simultaneous determination of fentanyl and its major metabolites in biological samples

A simple high performance liquid chromatographic (HPLC) procedure for the simultaneous determination of fentanyl and its wo major metabolites in biological samples was used in blood samples from 6 preterm sick newborn infants. A 8 mm x 100 mm, 4 mu m cyano column, 0.05 m phosphate buffer adjusted at pH 3.2 and acetonitrile (50:50 V/V) as mobile phase, were used at a flow rate 2.5 ml/min. Each run was completed within 10 minutes. The detection limits for the analysis were 0.10 ng, 0.15 ng and 0.10 ng for norfentanyl, fentanyl and despropiofentanyl, respectively, with 50 mu l injection for all the compounds at a signal-to-noise ratio of 3. The respective retention times were 4.62+/-0.10, 6.20+/-0.76 and 6.71+/-0.73 minutes for norfentanyl, fentanyl and despropiofentanyl. Microassay is simple, rapid and precise. This assay may be used for the therapeutic drug monitoring in newborn babies.