EPHEDRINE DETERMINATION IN HUMAN URINE USING A CARBON-PASTE ELECTRODEMODIFIED WITH C-18 BONDED SILICA-GEL

An electrochemical method by adsorptive stripping voltammetry with a m odified carbon paste electrode with C-18 bonded silica gel is describe d for the determination of ephedrine in human urine samples. The preco ncentration step is performed at open circuit and constant stirring (1 000 rpm) in 5x10(-4) M sodium hydroxide and the measurement step in am monia-ammonium chloride buffer (pH=10.0; 0.2 M) by linear scan voltamm etry to 150 mVs(-1) between 0.20 and 1.10 V. With the proposed method, ephedrine can be directly determined in urine, a relative standard de viation of 3.4% (n=12) and a detection limit of 270 mu gmL(-1) for a 2 minute preconcentration time, were obtained.