AUTOMATIC SPECTROPHOTOMETRIC PROCEDURE FOR DETERMINATION OF L-ASCORBIC ACID BASED ON REDUCTION OF IRON(III)-THIOCYANATE COMPLEX

Meissam Noroozifar,^a* Mozhgan Khorasani-Motlagh,^b and Abdol-Rahim Farahmand^a
a Analytical Research Laboratory, Department of Chemistry, Sistan & Baluchestan University, Zahedan, Iran, P.O. Box 98165-181,  E-mail: mnoroozifar@hamoon.usb.ac.ir.
^b Inorganic Research Laboratory, Department of Chemistry, Sistan & Baluchestan University, Zahedan, Iran.

Abstract
A very simple spectrophotometric method has been developed for indirect determination of L-ascorbic acid using flow injection system based on the redox reaction between iron(III)-thiocyanate complex and L-ascorbic acid in acidic medium. A negative peak results from an injection of L-ascorbic acid into an iron(III)-thiocyanate complex carrier stream when absorbance is monitored at 462 nm. The height of the negative peak is proportional to the concentration of L-ascorbic acid in the sample. Figures of merit such as a relative standard deviation of 2.0% (n=6), linearity range up to 100 μg/mL and detection limit of 0.36 μg/mL were obtained. No significant differences at the 95% confidence level were observed in comparison with results obtained by a manual procedure. The proposed system allowed the determination of L-ascorbic acid in pharmaceutical formulations and foods.

Key words: Indirect determination, L-ascorbic acid, Iron(III)-thiocyanate, Flow injection analysis, spectrophotometric method