Indirect determination of ephedrine in urine by differential pulse polarography

The 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 mu g per mL of urine. An extraction procedure with C-18 cartridge and a fast and easy nitrosation reaction with sodium nitrite in 0.2 M phthalate potassium hydrogen is also described. Determination of 5 mu g/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%.