Improved determination of methamphetamine, ephedrine and methylephedrine in urine by extraction-thermospectrometry

Abstract

A selective spectrophotometric method has been developed for the determination of stimulant drugs in urine. The method is based on colour development and thermochromism of ion-association compounds in the organic phase caused by mixing a 1,2-dichloroethane solution of the stimulant drug and a 1,2-dichloroethane solution of tetrabromophenolphthalein ethyl ester (TBPE.H). Methamphetamine, ephedrine and methyl-ephedrine bases extracted in a highly alkaline medium with 1,2-dichloroethane react with TBPE.H in 1,2-dichloroethane solution to form red ion-association complexes. The complexes show characteristic and stoicheiometric thermochromism with variation in temperature. Both the colour reaction and thermochromism in the organic phase were applied to the simultaneous and sensitive determination of two stimulant drugs in urine. The determination limits were about 0.16 µg ml^–1.