Acta Phys. -Chim. Sin. ›› 2008, Vol. 24 ›› Issue (02): 230-236.doi: 10.1016/S1872-1508(08)60012-1

• ARTICLE • Previous Articles     Next Articles

Electrodeposition of the Charge-Transfer Complex Generated during Electrooxidation of o-Tolidine and the Effects of Coexisting Chondroitin Sulfate

JIANG Xue-Qin; CAO Zhi-Jun; XIE Qing-Ji; YAO Shou-Zhuo   

  1. Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research, Ministry of Education of China, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, P. R. China
  • Received:2007-09-17 Revised:2007-10-22 Published:2008-01-26
  • Contact: XIE Qing-Ji

Abstract: The electrochemical quartz crystal microbalance (EQCM) technique was used to investigate the electrodeposition of the charge-transfer complex (CTC) generated during electrooxidation of o-tolidine (o-TD) in Britton-Robinson (B-R) buffers and effects of coexisting chondroitin sulfate (CS). A V-shaped frequency response to the cyclic voltammetric switching of o-TD indicated the precipitation and dissolution of the poorly soluble CTC, an oxidation intermediate, formed at the Au electrode during the redox switching of o-TD in a neutral or a weakly acidic medium (pH=4.07-6.50). The effects of potential scan rate, solution pH, and several supporting electrolytes were examined. The depth of the V-shaped frequency curves (-⊿f0V) was related to the supporting electrolyte used, with a decreasing sequence for -⊿f0V as 0.20 mol·L-1 NaNO3>0.20 mol·L-1 NaClO4>0.10 mol·L-1 Na2SO4. The -⊿f0V response to the redox switching of the CTC/o-TD“couple”was enhanced by the introduction of CS because of the formation of the CTC-CS adduct, as also characterized and supported by UV-Vis and FTIR spectrophotometry. The molar ratio (x) of the CTCto CSin the adduct and the electrode-collection efficiency of the CTC (η) were estimated using EQCM. The values of -⊿f0V increased with the increase in CS concentration, with a linear range from 0.75 to 15.2 μmol·L-1, and a detection limit down to 50 nmol·L-1. The new method proposed for CS assay was characterized by a dynamically renewed surface of the detection electrode.

Key words: Electrochemical quartz crystal microbalance, Charge-transfer complex, o-Tolidine, Assay of chondroitin sulfate, Dynamically renewed surface of the electrode


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