Determination of amphetamine, methamphetamine and ephedrine in urine by gas chromatography/mass spectrometry using ion-pair extraction

Abstract

A simple method for analysis of amphetamine, methamphetamine and ephedrine in urine was developed using ion-pair extraction and gas chromatography/mass spectrometry with electron impact ionization and selected ion monitoring (GC/MS-SIM). The 3', 3", 5', 5"-tetrabromophenolphthalein ethyl ester, a monoprotic dye, reacted with amphetamines in the liquid medium of pH 9.2-9.5 to form the red-violet complexes, which were soluble in dichloromethane. The dichloromethane extract was back-extracted and the extract was evaporated to dryness and derivatised with pentafluoropropionic anhydride (PFPA). The derivatised sample was evaporated to dryness, reconstituted in ethyl acetate, and injected into the GC. The calibration curves were linear between 50-2500 ng/ml (amphetamine and methamphetamine) and 100-2500 ng/ml (ephedrine). The detection limits were 16.45 ng/ml (amphetamine), 15.46 ng/ml (methamphetamine) and 22.21 ng/ml (ephedrine) and the reproducibility was not more than 10% RSD for each drug. The method was applied to 10 urine samples. Four samples were positively confirmed with greater than 500 ng/ml of methamphetamine and 200 ng/ml of amphetamine.