Modified Gold Electrode Applied in the Methimazole Determination”

PEREIRA SIRLEY V.; SEIA MA.; DE VITO IE.; JULIO RABA; MESSINA G. A.

Córdoba

Otro; I Reunión Internacional de Ciencias Farmacéuticas; 2010

Colegio Farmacéutico-UNC

MODIFIED GOLD ELECTRODE APPLIED IN THE METHIMAZOLE DETERMINATION Pereira SV, Seia M A, Llaver A P, DeVito I E, Raba J, Messina GA Departamento de Química, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis. Chacabuco 917, San Luis, Argentina, CP: 5700 Introduction Methimazole (MT, 1-methyl-2-mercaptoimidazol) is a drug used to treat hyperthyroidism. Its administered orally and concentrated in the thyroid gland [1], where its action is decrease the iodide incorporation into tyrosine and thus inhibits the production of thyroid hormones [2]. The development of rapid and sensitive methods that allow its determination in pharmaceutical samples is of vital importance. For this reasons in this article we describe the development of a dynamic system for in batch detection of methimazole in drug samples. Materials and methods All reagents used were of analytical reagent grade. Horseradish peroxidase, catechol, thioctic acid, dimethylaminopropyl carbodiimide hydrochloride and N-hydroxy-succinimide were purchased from Sigma Aldrich Inc. Cyclic voltammetry and timebase analysis were performed using the BAS 100 B (electrochemical analyzer Bioanalytical Systems). Modificación of gold electrode In the first stage of immobilization, gold electrode was immersed in a solution of thiotic acid (TA) 250 mM for 12 hours, then was rinsed with ethanol and dried with N2 gas. At this stage TA was covalently attached to the electrode surface through thiol groups, constituting a monolayer. After that, the TA modified electrode was placed in a succinimide-carbodimide solution -EDC: NHS (EDC 1% (v / v), NHS 2.5% (v / v)). In this step occurs the activation of carboxyl groups of TA, which will be used for the covalent bond with the amino groups of the enzyme. Finally, on the modified surface of the electrode were added 20 µL of a solution 0.25 mg / µl of horseradish peroxidase in phosphate buffer, pH 7.40 for 18 h at 4 ◦ C [3,4]. Determination of metimazol The modified electrode was introduced in an electrochemical cell, where the enzyme peroxidase (HRP) catalyzed the reduction of hydrogen peroxide (H2O2) to water (H2O) with the consequent oxidation of the mediator catechol (Q) to o-benzoquinone (P) The electrochemical reduction of P to Q was detected on the surface of the electrode using timebase technique. The current response obtained was directly proportional to the activity of the enzyme and consequently to the concentration of H2O2 added to the system [5]. When MT was added to the solution, the thiol groups of this compound participate in a Michael type addition reaction with P to form the corresponding thioquinone derivatives; decreasing the reduction current proportionally to the increase of the concentration of added MT[6]. Results and Discusion For determination of methimazole in pharmaceutical samples using a modified gold electrode for methimazole determination in citrate buffer pH 5.0, a calibration curve was obtained, the regression lineal equation was I (nA)=-338-6.38CMet with a coefficient of lineal regression of r=0.998 and the detection limit obtained was 1.9 µM. Conclusion The proposed system, which incorporates a modified gold electrode for the determination of methimazole in pharmaceutical samples, showed selectivity and sensitivity, also has advantages such as; do not require highly trained personnel or expensive instrumentation. In summary proposed methodology has good applicability in the pharmaceutical industry as a routine method.