Simultaneous Determination of Tramadol and Its Metabolite in Human Urine by the Gas Chromatography-Mass Spectrometry Method

Abstract

A sensitive and efficient method was developed for determination of tramadol and its metabolite (O-desmethyltramadol) in human urine by gas chromatography-mass spectrometry. Tramadol, O-desmethyltramadol and medazepam (internal standard) were extracted from human urine with a mixture of ethylacetate and diethylether mixture (1 : 1, v/v) at basic pH with liquid-liquid extraction. The calibration curves were linear (r = 0.99) over tramadol and O-desmethyltramadol concentrations ranging from 10 to 200 ng/mL and 7.5 to 300 ng/mL, respectively. The method had an accuracy of >95% and intra-and interday precision (relative standard deviation %) of <= 4.93 and <= 4.62% for tramadol and O-desmethyltramadol, respectively. The extraction recoveries were found to be 94.1+/-2.91 and 96.3+/-3.46% for tramadol and O-desmethyltramadol, respectively. The limit of quantification using 0.5 mL human urine was 10 ng/mL for tramadol and 7.5 ng/mL for O-desmethyltramadol. After oral administration of 100 mg of tramadol hydrochloride to a patient, the urinary excretion was monitored during 24 h. About 15% of the dose was excreted as unchanged tramadol.