Voltammetric Determination of Diltiazem Employing Diamond Electrode

Diltiazem hydrochloride (DTZ) is a drug used for treating hypertension, angina and arrhythmia. The control of amount of DTZ in pharmaceuticals is very necessary because an overdose of this antihypertensive may cause hypotension, chest pain and canalsolead to dead mainly in sick sinus syndrome patients[1].For this, several methods were developed for the determination of DTZ, including spectrophotometry, chromatography and voltammetry. The voltammetry present advantages over other techniques, such as rapidity, sensitivity and low cost. In this work, for the first time a boron-doped diamond electrode (BDDE) was used for DTZ voltammetric determination. The experiments were conductedin a glass electrochemical cell coupled to a Teflon® support containing three electrodes, a platinum plate as counter electrode, an Ag/AgCl (KCl 3.0 mol L-1) as reference electrode and a BDDE as working electrode. The voltammetric measurements were carried out using a FRA2 μAutolab type III potentiostat/galvanostatcontrolled bythe GPES software. The BDDE was electrochemically pretreated using a Microquímica potentistat/galvanostatand chronopotentiometry. For anodic pretreatment,0.5 A cm-2 was applied during 30 sand for cathodic pretreatment, -0.5 a cm-2 was applied during 120 s. Cathodic pretreatment provided better repeatability and high current value for DTZ, thus this pretreatment was used in following analysis. Phosphate buffer solution was chosen for pH study.For that, the oxidation peak forDTZ 49.8 μmol L-1was evaluatedin pH range of 2.0–10.0and the pH value that presented the highest current value and better repeatability was3.0. In these conditions, DTZ presented an irreversible oxidation process at 1.4 V. A scan rate study demonstrated that the DTZ transport towards BDDE is diffusion controlled and its oxidation involves two electrons [2]. Under optimal conditions of instrumental parameters of square-wavevoltammetry (SWV), the analytical curve was constructed by successive additions of DTZ aliquots and the current values were linearly dependent with concentration in the range of0.99 –16.3 μmol L-1. The obtained limit of detection was 0.019 μmol L-1. The proposed method was successfully applied in the determination of DTZ in pharmaceutical formulations. The results obtained by the proposed method were not statistically different from those obtained by chromatographic method at a 95 % confidence level.