Analytical Sciences

Atomic Absorption Spectrometry for the Automatic Indirect Determination of Ascorbic Acid Based on the Reduction of Manganese Dioxide

Meissam NOROOZIFAR,* Mozhgan KHORASANI-MOTLAGH,** and Kambiz AKHAVAN*

*Analytical Research Laboratory, Department of Chemistry, Sistan & Baluchestan University, Zahedan, P. O. Box 98165-181, Iran
**Inorganic Research Laboratory, Department of Chemistry, Sistan & Baluchestan University, Zahedan, Iran

A new and simple flow injection method followed by atomic absorption spectrometry has been developed for the indirect determination of ascorbic acid. The proposed method is based on oxidation of ascorbic acid to dehydroascorbic acid using a solid-phase manganese dioxide (30% m/m suspended on silica gel beads) reactor. The flow of the sample through the column reduces the MnO₂ to Mn(II) in an acidic carrier stream of 6.3 mM HNO₃ (pH 2.2) with flow rate of 4.0 ml/min at room temperature; Mn(II) is measured by atomic absorption spectrometry. The absorbance of Mn(II) is proportional to the concentration of ascorbic acid in the sample. The calibration curve was linear up to 30 mg/L, with a detection limit of 0.2 mg/L for a 220 µL injected sample volume. The developed procedure was found to be suitable for the determination of AsA in pharmaceuticals and foods with a relative standard deviation better than 1.09% and a sampling rate of about 95 h^-1. The results exhibit no interference from the presence of large amounts of organic compounds. The reliability of the method was established by parallel determination against the 2,6-dichlorophenolindophenol methods.

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