Electrochemical determination of ascorbic acid in orange juice using a pencil electrode modified with chromium (III) hexacyanoferrat

Ascorbic acid (AA) is a water-soluble vitamin essential in the human nutrition, an antioxidant, a scavenger of free radicals in biological systems and a cofactor of several enzymes. For the precise detection of AA concentration in biological samples there is important the option of the determination method [1-3]. In electrochemistry the working electrodes may be modified to improve the analytical signal, the detection range, the sensitivity, and the selectivity of this technique. Thus, the present work sought to use a pencil electrode modified with Cr (III) hexacyanoferrate (CrHCF) to determination of AA. The influence of parameters on the voltammetric electrode response, supporting electrolyte, scan rate, precursor reagent, in drugs containing AA have been evaluated. A CrHCF-modified pencil electrode was used to determination of Ascorbic acid tablets by Differential pulse voltammetry (DPV) technique. The influence of several parameters on the voltammetric electrode response was studied. The linear range found was of 0.3 mM to 2,00 mM of AA, with r = 0.999 and relative deviation of 0.01,RSD is 4.76% . The limits of detection and quantification were 0.073 and 0.246 mM, respectively. The electrochemical behavior of film of CrHCF was studied in different electrolytes. The experimental results showed that (phosphate/KCl 0.1 M) electrolyte, pH= 3 is a good supporting electrolyte. The study of the scan rates on the voltammetric response of the CrHCF-modified electrode shows an increase in the anodic peak current with the scan rate in low scan rates, suggesting that there is an adsorption process on the electrode surface. In high scan rates the anodic peak current proportion with root of scan rates, this shows a diffusional process. The prepared electrode was applied to determination of AA in real samples such as vitamin C tablets. This was done by standard addition method. The experimental curve showed that the Real sample (orange juice ) has 0.21 mM concentration of AA.Real Samle