Indirect determination of ephedrine in urine by differential pulse polarography

Abstract

AbstractThe nitrosation of ephedrine and the electrochemical reduction of N‐nitrosoephedrine were investigated by differential pulse polarography and have been optimized in order to attain the optimum analytical signal. Reduction of the N‐nitrosoephedrine was carried out in one irreversible, diffusion‐controlled step using potassium chloride‐hydrochloric acid. In 0.1 M hydrochloric acid the N‐nitrosoephedrine shows a well‐defined reduction peak at −0.77 V (vs. Ag/AgCl/ 3 M KCl). An indirect differential‐pulse polarographic method is described for the determination of ephedrine at levels higher than 2.5 μg per mL of urine. An extraction procedure with C18 cartridge and a fast and easy nitrosation reaction with sodium nitrite in 0.2 M phthalate potassium hydrogen is also described. Determination of 5 μg/mL of N‐nitrosoephedrine in urine samples of 4 mL was possible using the standard addition method, with a relative error of −4.0% and relative standard deviations no higher than 2.1%.