Possibilities of the use of fast scan voltammetry in simultaneous determination of purines at carbon fiber ultramicroelectrodes

Abstract

Hipoxantina, xantina e ácido úrico são purinas encontradas em fluídos extracelulares, que podem ser utilizados como marcadores metabólicos, indicadores da idade de carnes e outras aplicações. Estudos voltamétricos foram desenvolvidos para investigar a possibilidade da determinação simultânea destes analitos em ultramicroeletrodos de fibra de carbono (diâmetro de 7 µm). Os estudos efetuados mostraram a possibilidade destas determinações com coeficientes médios de recuperação da ordem de 97,6%, ao nível de µmol L -1 .Hypoxanthine, xanthine and uric acid are purines present in extracellular fluids that can be used as metabolic markers, in evaluation of meat conservation and other applications. Voltammetric studies were performed in order to investigate the possibility of simultaneous determination of these compounds using carbon fiber ultramicroelectrodes (7 µm diameter). The studies revealed the possibility for performing such determinations with mean recoveries of 97.6% in mixtures of the three compounds at µmol L -1 level.Keywords: xanthine, hypoxanthine, uric acid, carbon electrodes, fast scan voltammetry *e-mail: cavalheiro@dq.ufscar.br Presented at the XI Simpósio Brasileiro de Eletroquímica e Eletroanalítica, Maragogi -AL, Brazil, April 5-9, 1999. Guest editor: Luis Alberto Avaca. IntroductionOxypurines xanthine (XA), hypoxanthine (HX) and uric acid (UA) are products of metabolism of nucleotides 1 and can be found in extracellular fluids. Their determination is important since they can be related with the depletion of adenosine triphosphate (ATP) in tissues 2 and are the final products of purine metabolism in humans. Overproduction of UA can cause gout 3,4 .Chromatographic methods for purine determination are summarized in reviews 5 . Electrochemical methods include stripping of Cu(II) complexes 6-10 , adsorptive stripping of purines from Hg 11 . Immobilization of the enzyme xanthine oxidase to electrodes has also been used [12][13][14][15] , as it catalyses the conversion of XA and HX to UA. Recently we evaluated the performance of carbon electrodes and carbon fiber ultramicroelectrodes in amperometric determination of XA and HX, in relation to the surface activation in different techniques 16 .In the present study the possibilities of simultaneous determination of XA, HX and UA are investigated at carbon fiber ultramicroelectrodes. The interference of uric acid generated in xanthine oxidation is evaluated using fast scan voltammetry in phosphate buffer at physiological pH, with the advantages of a miniaturized system. ExperimentalAll the chemicals were of analytical grade and used without further purification. The experiments were performed in 70 mmol L -1 phosphate buffer at pH 7.4.The instrumental setup as well as the carbon fiber ultramicroelectrode (CF-UME) preparation have been described earlier 17 . Briefly, a triangular waveform from a function generator (Universal Programmer PAR-175 EG&G) was applied to a two electrode cell (80 µL internal volume). The current at the CF-UME was monitored using an o...

Direct measurements of xanthine in 2000-fold diluted xanthinuric urine with a nanoporous carbon fiber sensor

“…22 FSV of 400 nM xanthine shows resolved xanthine and uric acid peaks, although the S/N is low. At 10 V s −1 the sensitivity is 0.038 nA lM −1 .…”

“…22 A stable background current at 0.83 ± 0.06 V, the potential of the xanthine oxidation peak, is needed for good S/N. 22 A stable background current at 0.83 ± 0.06 V, the potential of the xanthine oxidation peak, is needed for good S/N.…”

Voltammetric and impedance studies of inosine-5′-monophosphate and hypoxanthine

“…Sensors have been developed using microelectrodes [8], chemically modified electrodes [9,10] and by mechanical or electrochemical activation of the electrode surfaces [11,12]. However, most of the reported research has used oxidase-based enzyme biosensors for hypoxanthine detection with measurement of oxygen consumption or product formation [13 -25].…”

Caffeine determination at a carbon fiber ultramicroelectrodes by fast-scan cyclic voltammetry

“…27 At ultramicroelectrodes, under typical slow scan rates of voltammetry, signal-to-noise ratios (S/N) can increase up to one decade because of efficient mass transport to the electrode resulting from edge effects. In addition, because of the small dimensions and low IR drop, fast scan voltammetric procedures [28][29][30][31][32][33] and measurements in highly resistive media are possible at UMEs. 34 According to Wightman and Wipf, 31 fast scan voltammetry is useful in preventing accompanying chemical reactions, understanding mechanism and kinetics of heterogeneous electron transfer, reduction in time of analysis, faster response to potential changes, minimizing in the size of devices for in vivo analysis, use of non-expensive instrumentation, among others.…”