Meh Y. V., Vishnikin A. B., Posudiievska O. R.

Oles Honchar Dnipropetrovsk National University

DETERMINATION OF ASCORBIC ACID IN THE OBJECTS OF ANALYSIS WITH A COMPLEX MATRIX USING 12-MOLYBDOPHOSPHORIC ACID AND BISMUTH (III)

Ascorbic acid (AsA) is a water-soluble vitamin. This is the main vitamin of vegetables, fruits and berries. AsA has strong antioxidant properties, it is essential for functioning of the living organism. It participates in the regulation of redox processes, increases the body’s resistance to infections.

The widespread use of AsA in pharmacological and food industries is the reason of development of a great number of methods for the evaluation of content level of AsA in different samples. These methods include, in particular, spectrophotometry and luminescence method, as well as electrochemical methods and chromatography. Spectrophotometric method is optimal for objects of analysis, being not very complicated in composition due to its simplicity, rapidity, availability, as well as its cost, sensitivity and selectivity. Especially, this method is often used for the analysis of beverages, fruits, pharmaceuticals and certain biological objects. However, until now spectrophotometric methodologies which would allow to determine AsA in complex matrices such as wine or many kinds plants, haven’t been proposed yet.

Earlier it was proposed to determine AsA using synthesized heteropoly complexes, in particular, 11-phosphorusmolibdobismut heteropolyanions. Since the synthesis of these substances may require special skills in the field of inorganic chemistry and thus reduces the availability of reagents and of the whole procedure, we have proposed to modify the above-mentioned method, using synthesis of analytical reagent «in situ». As the main mother substance we have used commercially available 12-molybdophosphoric acid.

We have found out the peculiarities of formation and reduction of ternary heteropoly complex. We have also defined the optimal conditions for the formation of 2-electron heteropolysyn, having its signals at the analytical wavelength 720 nm. It has been established that the complex is formed at a 1:1 ratio of 12-molybdophosphoric acid and Bi3+, the reducing reaction proceeds during 5 minutes at the pH from1,6 to 1,8. The interval of acidity at which the total reduction of heteropoly complex becomes possible can be increased from pH 1 to pH 2, if the reaction mixture is digested for a longer period of time – 35 min. The reaction of bismuth-containing heteropolyanion synthesized in the solution, with AsA is one of the most selective reactions for the AsA determination, which allows for the first time to develop the methods for its identification in wines, beverages, herbal mixtures and biological objects.