L-ascorbic acid determination in pharmaceutical formulations using a biosensor based on carbon paste modified with crude extract of zucchini (Cucurbita pepo)

• Published in: Journal of the Brazilian Chemical Society Vol. 11; no. 4; pp. 412 - 418
• Main Authors: Fatibello-Filho, Orlando, Vieira, Iolanda da C.
• Format: Journal Article
• Language: English; Portuguese
• Published: Sociedade Brasileira de Química 01.08.2000
• Subjects: carbon paste biosensor; CHEMISTRY, MULTIDISCIPLINARY; L-ascorbic acid; peroxidase; zucchini (Cucurbita pepo); L-ascorbic acid; carbon paste biosensor; peroxidase; zucchini (Cucurbita pepo)
• ISSN: 0103-5053; 1678-4790; 1678-4790
• DOI: 10.1590/S0103-50532000000400015

A biosensor based on carbon paste modified with crude extract of zucchini (Cucurbita pepo) as a source of peroxidase is proposed for determining L-ascorbic acid in pharmaceutical formulations. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-quinone whose electrochemical reduction back to hydroquinone was obtained at peak potential of -0.14V. Thus, when L-ascorbic acid is added to the solution, this acid can reduce chemically p-quinone to hydroquinone and/or reduce hydrogen peroxide, decreasing the peak current obtained proportionally to the increase of its concentration. The recovery of L-ascorbic acid from five samples ranged from 98.1 to 102.1% and a rectilinear calibration curve for L-ascorbic acid concentration from 2.0x10-4 to 5.5x10-3 mol L-1 (r=0.9992) was obtained. The detection limit was 2.2x10-5 mol L-1 and relative standard deviation was < 1.3% for a solution containing 4.0x10-3 mol L-1 L-ascorbic acid, 7.0x10-3 mol L-1 hydroquinone and 2.0x10-4 mol L-1 hydrogen peroxide. The results obtained for L-ascorbic acid in pharmaceutical formulations using the proposed biosensor and those obtained using the Pharmacopeia method are in agreement at the 95 % confidence level.