O presente trabalho apresenta uma metodologia simples, rápida e de baixo custo para a determinação de citrato de sildenafila (SC) em formulações farmacêuticas de referência (Viagra ® ) e em produtos similares, genéricos e manipulados, por amperometria de múltiplos pulsos em sistema FIA (análise por injeção em fluxo). O método consiste na aplicação de três pulsos de potencial (sequenciais) em função do tempo sobre um eletrodo de trabalho de diamante dopado com boro. SC foi detectado em 1,6 e 1,9 V por meio de dois diferentes processos irreversíveis de oxidação. Um terceiro pulso de potencial (1,0 V) foi aplicado para regeneração da superfície do eletrodo. Foram obtidos limites de detecção na ordem de 10 nmol L -1 e desvio padrão relativo menor que 0,2% (n = 10) para SC 4,5 × 10 -5 mol L -1 , permitindo 86 injeções por hora. Estudos de adição e recuperação nas amostras ficaram próximos de 100% e os resultados foram validados por cromatografia.This work presents a simple, fast and low-cost method for determining sildenafil citrate (SC) in Viagra ® and in similar, generic and manipulated pharmaceutical formulations using flow injection analysis (FIA) with multiple pulse amperometric detection. The method consists on the application of three sequential potential pulses as a function of time. SC is detected at 1.6 and 1.9 V by two different irreversible oxidation processes. The third potential pulse (1.0 V) is applied for the regeneration (cleaning) of the surface of the boron-doped electrode. The limit of detection on an order of 10 nmol L -1 was reached with a relative standard deviation of less than 0.2% (n = 10) for 4.5 × 10 -5 mol L -1 CS. The analytical frequency was calculated in 86 injections per hour. The addition recovery studies in all the samples were approximately 100% and the results were validated by chromatographic methods.Keywords: sildenafil citrate, multiple pulse amperometry, flow injection analysis
IntroductionSildenafil citrate (SC) (Viagra ® , Figure 1) is the pioneer drug in erectile dysfunction treatment introduced by Pfizer in 1998. Since then, Viagra ® has become one of the most marketed drugs worldwide, reaching 6 million prescriptions in its first 6 months on the market and generating billions of dollars in revenue. [1][2][3] As a result of such demand, Viagra ® is among the most adulterated drugs in the world. 4,5 Moreover, Pfizer Viagra ® manufacturing patent expired in June 2010, and several pharmaceutical laboratories and pharmacies began to produce and market generic, similar and manipulated versions of the drug comparable to Viagra ® , the reference listed drug. However, there is no record of an official method for drug-quality control of Viagra ® in the Brazilian Pharmacopeia, nor in international compendium of the same nature. It is thus fundamental to develop novel, fast, simple and low-cost Lopes Júnior et al. 1801 Vol. 23, No. 10, 2012 analytical methods for drug quality control in order to protect the health of consumers.In the literature there are numerous methods for the i...
