Department of Chemistry, Faculty of Science and Art, Gazi University, Ankara, Turkey

(Received: August 28, 2007; Accepted: November 18, 2007)

ABSTRACT

   An indirect method for the determination of ascorbic acid in fruit juice and vitamin C tablets by flame atomic absorption spectrometry was described.  This method is based on the reduction of chromium (VI) to chromium(III) with the reducing action of ascorbic acid, separation of unreacted Cr(VI) as its 1,5-diphenilcarbazide complex on a column filled with Amberlite XAD-16, elution of the complex by 10 mL of 0.05 mol L-1 H2SO4 in methanol, and determination by flame atomic absorption spectrometry. Amount of the ascorbic acid was calculated from the amount of Cr(VI) reacted with ascorbic acid.  The optimum conditions for the determination of ascorbic acid, including pH and volume of sample solution were examined.  The effect of interfering species on the recovery of the ascorbic acid was also investigated.  The proposed method allows high sensitive and selective determination of ascorbic acid in the range 0.5-20 μg/mL.  The proposed method is precise as it provides relative standard deviation of 3.4% during five replicate determinations of 12 μg/mL of ascorbic acid.  Accuracy of the procedure was tested by analyzing spiked real samples and applying 967.21 Official Method (AOAC) for the determination of ascorbic acid.  The procedure described was successfully applied for the determination of ascorbic acid in pharmaceutical preparation, lemon flavored soft powder drink and fruit juices. Ascorbic acid has been determined in real samples with relative error lower than 8%.

Key words: ascorbic acid, flame atomic absorption spectrometry, Amberlite XAD-16, indirect determination, solid phase extraction