engleski

Square-Wave Voltammetry of Cocaine

Electrochemical properties of cocaine and its metabolites such as benzoyl ecgonine (BE), ecgonine, and methyl ester ecgonine have been studied by means of square-wave voltammetry at a hanging mercury drop electrode. In a phosphate buffer at pH = 7 cocaine give rise to a single voltammetric peak at about - 1.490 V vs Ag/AgCl (3 mol/L KCl). At higher pH, BE is spontaneously formed, as a first hydrolysis product of cocaine. BE can further hydrolyse to ecgonine that is electrochemically inactive at the mercury electrode. Methyl ester ecgonine, an another hydrolysis product of cocaine, is electrochemically inactive at the mercury electrode, too. BE undergoes reduction owing to its ester group, giving raise to a voltammetric peak within the potential interval from - 1.010 V to - 1.200 V, depending on the concentration of BE. Thus, at pH = 8.5, cocaine solution gives rise to two SW peaks due to the reduction of unhydrolysed cocaine and BE. The reduction of BE undergoes through a complex electrode mechanism coupled by adsorption and two types of following chemical reactions. The reduction electrode product of BE undergoes (i) dimerization and than (ii) protonation leading to final chemical electrochemically inactive products, most probably ecgonine and benzaldehyde. The rate of the latter chemical reaction is controlled by the proton concentration in the electrolyte solution. Comparing the voltammetric properties of cocaine to that of BE and methyl ester ecgonine, it has been concluded that the electrochemicall activity of cocaine originates from the reduction of the same ester group as in the case of BE. The main difference between cocaine and BE is manifested in their tendency for adsorption on the mercury electrode surface. BE adsorbs stronger than cocaine, and hence an adsorptive stripping voltammetric method for determination of cocaine was developed on the basis of BE reduction.

cocaine; benzoylecgonine; ecgonine; methyl ester ecgonine; square-wave voltammetry

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