Electrocatalytic determination of cysteamine using multiwall carbon nanotube paste electrode in the presence of 3,4-dihydroxycinnamic acid as a homogeneous mediator

Abstract

A eletrooxidação da cisteamina (CA) foi estudada por eletrodos de pasta de nanotubos de carbono modificados com ácido 3,4-diidroxicinâmico (3,4-DHCA) usando voltametria cíclica, cronoamperometria e voltametria de varredura linear. Usando o eletrodo modificado, a cinética de eletrooxidação da CA foi consideravelmente intensificada através da redução do potencial anódico por meio de uma reação catalítica. O mecanismo de comportamento eletroquímico da CA na superfície do eletrodo modificado foi analisado por vários métodos eletroquímicos, na presença de mediador. O eletrodo modificado preparado apresentou respostas voltamétricas com alta sensibilidade para CA, o que o torna muito adequado para a detecção de CA em quantidades de traço. Um intervalo dinâmico linear de 0,25-400 µmol L −1 para a CA foi obtida em solução tamponada com pH 7,0. O limite de detecção foi de 0,09 µmol L −1 .The electrooxidation of cysteamine (CA) was studied by modified carbon nanotubes paste electrode in the presence of 3,4-dihydroxycinnamic acid (3,4-DHCA) using cyclic voltammetry, chronoamperometry and linear sweep voltammetry. Using the modified electrode, the kinetics of CA electrooxidation was considerably enhanced by lowering the anodic over-potential through a catalytic fashion. The mechanism of CA electrochemical behavior at the modified electrode surface was analyzed by various electrochemical methods in the presence of mediator. The prepared modified electrode showed voltammetric responses with high sensitivity for CA, making it very suitable for the detection of CA at trace levels. A linear dynamic range of 0.25-400 µmol L −1 for CA was obtained in buffered solutions with pH 7.0. The limit of detection was 0.09 µmol L −1 . Keywords: cysteamine, electrocatalysis, voltammetry, multiwall carbon nanotubes, 3,4-dihydroxycinnamic acid IntroductionCysteamine is an important thiol drug for the treatment of cystinosis.1 The deficiency of a cystine carrier in the lysosomal membrane leads to cystine accumulation within the lysosomes, ultimately crystallizing in vital organs such as the liver, kidney, spleen, intestines, and cornea.2,3 A number of long term clinical trials have shown that cysteamine administration (as cysteamine hydrochloride) stabilizes renal function, delays glomerular deterioration and improves linear growth. 4 Cysteamine and its disulfide, cystamine, have been shown to be neuroprotective in a number of cell culture and animal models.5 With this goal in mind, a rapid but specific and sufficiently sensitive analytical method was required for total cysteamine determination in biological and pharmaceutical samples. Numerous methods have been reported for the determination of CA in pharmaceutical and biological samples including chromatography, 6-8 electrophoresis, 9 gas chromatography with flame photometric detection, 10 ion exchange chromatography, 11 and electrochemical methods 12-14 using modified electrodes. Due to problems in chromatographic methods such as selecting a suitable column or a mobile phase with liquid chrom...

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