Copper-modified gold electrode specific for monosaccharide detection - Use in amperometric determination of phenylmercury based on invertase enzyme inhibition

The electrochemical oxidation of mono- and disaccharides at various copper-modified electrodes is reported: glassy carbon modified at open circuit or by electrochemical deposition of copper, gold modified by electrochemical deposition, and at bulk copper electrodes. A comparative study of these four electrodes was made by linear sweep voltammetry and amperometry. The maximum oxidation peak separation between disaccharides and monosaccharides is about 200 mV. After optimization, amperometric determination of monosaccharides was done at +0.30 versus Ag/AgCl in 0.15 M NaOH at the copper-modified gold electrode. Using the developed method, the enzymatic activities of invertase and P-galactosidase were determined through their reaction with sucrose and lactose, respectively. Validation was carried out by a spectrophotometric method based on 3,5-dinitrosalicylic acid, and it was shown that the proposed electrochemical method is more sensitive. The analytical utility of the copper-modified gold electrode was tested for the determination of organic mercury. Addition of phenylmercury standards to the invertase solution caused a decrease in the enzyme activity, and allowed the determination of phenylmercury in pharmaceutical samples. The concentration has been determined in the 10-55 ng ml(-1) range. (C) 2003 Elsevier B.V. All rights reserved.