Analytica Chimica Acta 439 (2001) 291–297 Chemically modified electrodes based on macrocyclic compounds for determination of Vitamin C by electrocatalytic oxidation Vijaykumar S. Ijeri, Priya V. Jaiswal, Ashwini K. Srivastava ∗ Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai-400098, India Received 13 September 2000; received in revised form 19 February 2001; accepted 13 March 2001 Abstract The voltammetric behavior of Vitamin C (l-ascorbic acid) at carbon paste electrodes and electrodes modified with aza macrocycles have been studied. The use of zinc complexes, formed in situ at the electrode surface reduced the overpotential for the oxidation of ascorbic acid by about 200 mV and enhanced the peak currents. Linearity was observed over the range of 0.6–500 g/cm 3 with a detection limit of 0.1 g/cm 3 by differential pulse voltammetry. The modified electrode was used for the determination of Vitamin C in multivitamin–multimineral pharmaceutical preparations, fruit juices and wine samples. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Vitamin C; Chemically modified electrodes; Macrocyclic compounds; Voltammetry; Electrocatalysis 1. Introduction Vitamin C or l-ascorbic acid is distributed widely in both the plant and animal kingdoms. In vegetable cells, it occurs in free form and also often bound to protein as “ascorbigen”. Among animal organs, the liver, leukocytes and anterior pituitary lobe show highest concentration of ascorbic acid. Vitamin C, a water-soluble vitamin that is widely required in metabolism and consumed on a large scale is elec- troactive and a variety of methods have been developed for its analysis. Spectrophotometric methods have been developed for the analyses of Vitamin C in phar- maceutical preparations and fruit juices [1,2]. Enzyme based electrodes [3], polymer based electrodes [4], dye based electrodes [5], etc. have been proposed for the electrochemical detection and determination of ascor- bic acid. The electrocatalytic oxidation of ascorbic ∗ Corresponding author. Fax: +91-652-8547. E-mail address: aks@chem.mu.ac.in (A.K. Srivastava). acid at polypyrrole coated platinum disc electrodes [6] doped with chloride and dodecylbenzene sulphonate have been studied by Lyons and co-workers, Lorenzo and co-workers have carried out mechanistic studies [7] of the electrocatalytic oxidation of -nicotinamide adenine dinucleotide and ascorbate at glassy car- bon electrodes modified with electrodeposited films derived from 3,4-dihydroxybenzaldehyde and ap- plications of its other isomers in real analyses [8]. Glassy carbon electrodes modified with a cellu- lose acetate film [9] and screen-printed [10] car- bon electrodes bearing 2,6-dichlorophenolindophenol have been developed and used for analyses of var- ious samples. Carbon paste electrodes modified with an aqueous insoluble redox mediator, ruthe- nium(III)diphenyldithiocarbamate showed a lin- ear response over the range 2.5–125 mg/dm 3 [11]. Voltammetric methods utilizing electrogenerated ferricinium carboxylic acid [12] and gold micro- electrodes [13] have been proposed for the assay of Vitamin C. 0003-2670/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0003-2670(01)00989-8