Determinação voltamétrica de fármacos via oxidação eletrocatalítica do contra-íon tartarato em eletrodo modificado com ftalocianina de cobalto (II)

Tartaric acid (TA, C4H6O6) is a hydrocarboxylic acid largely found in wines and naturally present in fruits, especially grapes, bananas, pears, tangerines, and tamarinds [1,2]. TA salts are widely used in the pharmaceutical industry as an excipient or as a counter ion to the active principle of some medicines, among them are metoprolol tartrate, norepinephrine hemitartrate and epinephrine tartrate[3]. Voltammetric determination of pharmaceutical drugs via detection of the counter-ion of the drug is a growing area of research[4]. We have demonstrated thatthe non-electroactive tartaric acid/tartrate ions can be electrocatalytic oxidized at a cobalt (II) phathalocyanine modified electrode (CoPC)[5]. Here we demonstrate such electrocatalytic oxidation is useful for a highly sensitive indirect determination of pharmaceuticals containing tartrate as a counter-ion by square-wave voltammetry. The effect of experimental variables, such as dispersion and loading of CoPC, together with optimum conditions for sensing the analyte are discussed. The absence of significant memory effect combined with the easiness of electrode preparation (3% CoPC, 57% carbon powder and 40% mineral oil) led to the development of a sensitive and straightforward method with a linear response range between 15 to 90μmol L-1(r=0.9993) and a detection limit of 27,2μmol L-1, Fig. 1. The methodwas successfully applied for an indirect monitoring of metoprolol in pharmaceutical tablets of metoprolol tartrate and can be applied to other tartrate counter-ion based pharmaceuticals.