Stripping Voltammetric Methods for Determination of the Antiparasitic Drug Nitazoxanide in Bulk Form, Pharmaceutical Formulation and Human Serum

摘要

Voltamogramas ciclicos de nitazoxanida medidos no eletrodo de gota de mercurio no tampao universal Britton-Robinson corn valores de pH de 2 a 11 contendo 20% (v/v) de etanol exibiram um unico pico catodico irreversivel de 4-eletrons, correspondendo a reducao de seu grupo NO_2 para hidroxilamina. Observou-se que a nitazoxanida adsorve na superficie do eletrodo de mercurio numa monocamada com cobertura superficial de 3,16 × 10~(-10) mol cm~(-2) na qual cada molecula adsorvida ocupa uma area de 0.525 nm~2. Baseado no seu comportamento de adsorcao na superficie do eletrodo de mercurio, metodos voltametricos validados 'stripping' catodico adsortivo com varredura linear (VL), pulso diferencial (PD) e onda quadrada (OQ) foram descritos para determinacao de nitazoxanida no seio da solucao. Limites de detecao de 1,5×10~(-10), 2,4×10~(-10)e 3,0×10~(-11) mol e limites de quantificacao de nitazoxanida de 5,0×10~(-10), 8,0×10~(-10) e 1, 0×10~(-10) mol L~(-1) no seio da solucao foram obtidos a partir dos metodos VVL, VPD e VOQ descritos acima, respectivamente. Os metodos descritos foram aplicados com sucesso para a determinacao de nitazoxanida em sua formulacao farmaceutica (po de Cryptonaz) e em serum humano sem a necessidade de pre-tratramento da amostra, etapas de extracao ou a formacao de cromogenos coloridos antes da analise. Alem disto, determinou-se nitazoxanida com sucesso e sem interferencia de produtos de degradacao induzidos por acido ou base, indicando a estabilidade e poder dos metodos voltametricos descritos.Cyclic voltammograms of nitazoxanide recorded at the hanging mercury drop electrode in the Britton-Robinson universal buffer of pH values 2 to 11 containing 20% (v/v) ethanol exhibited a single 4-electron irreversible cathodic peak corresponding to the reduction of its NO2 group to the hydroxylamine stage. Nitazoxanide was found to adsorb onto surface of the mercury electrode in a monolayer surface coverage of 3.16×10~(-10) mol cm~(-2) in which each adsorbed molecule occupies an area of 0.525 nm~2. Based on its adsorption behavior onto the mercury electrode surface,validated linear sweep (LS), differential pulse (DP) and square wave (SW) adsorptive cathodic stripping voltammetric methods were described for determination of bulk nitazoxanide. Limits of detection of 1.5×10~(-10), 2.4×10~(-10) and 3.0×10~(-11) mol L~(-1) and limits of quantification of 5.0×10~(-10), 8.0×10~(-10) and 1.0×10~(-10) mol L~(-1) nitazoxanide in the bulk form were achieved by means of the described LS, DP and SW adsorptive cathodic stripping voltammetric methods,respectively. The described methods were successfully applied for determination of nitazoxanide in its pharmaceutical formulation (Cryptonaz powder) and in spiked human serum without the necessity for sample pretreatment, time consuming extraction steps or formation of colored chromogens prior to the analysis. Besides, nitazoxanide was successfully determined without interference from its acid or base-induced degradation products indicating the stability-indicating power of the described voltammetric methods.