REACTION FEATURES OF 18-MOLIBDODIPHOSPHATE AND FOLIN-CIOCALTEU REAGENT WITH PHENOLIC COMPOUNDS

The comparative investigation of a reaction between 18-molybdophosphate heteropoly complex (18-MPC) and Folin-Ciocalteu reagent (FCR) with a diversity of the representatives of different phenolic compounds classes shows a similar reaction behavior for both reagents. This evidence can be used for the application of 18-MPC along with FCR for the evaluation of total content of phenols. It was established that 18-MPC is more active as an oxidizing agent with respect to phenols and for this reason in comparison with FCR the range of optimal values of pH is displaced into the more acidic region, the reaction rate is higher, and the concentration of the reagent is one order of magnitude less. It was also discovered that by using both reagents and measuring the absorbance in absorption maximum of heteropoly blue (HPB), the graduation curves were nonlinear. The observed phenomenon was explained by the changes in the composition and depth of the HPB reduction occurring when changing the ratio between the heteropoly complex and the phenol. The isobestic point present in the absorption spectra of HPBs and which was acquired from 18-MPC allows obtaining strictly linear calibration curves. By using 18-MPC the influence of reducing sugars, simple monophenols, sulphite ions, vitamins and some other compounds on the result of the determination of phenolic compounds becomes much smaller. It was shown by example of the ascorbic acid and rutin determination in the mixture that only by using 18-MPC it was possible to determine phenol and more active reducing agent separately by varying the pH of the determination. Keywords: 18-molybdophosphate heteropoly complex, Folin-Ciocalteu reagent,spectrophotometric analysis, determination of phenols(Russian)DOI: http://dx.doi.org/10.15826/analitika.2015.19.3.001T.A. Denisenko, A.B. Vishnikin, L.P. TsiganokOles Honchar Dnipropetrovsk National University,Dnipropetrovsk, Ukraine The comparative investigation of a reaction between 18-molybdophosphate heteropoly complex (18-MPC) and Folin-Ciocalteu reagent (FCR) with a diversity of the representatives of different phenolic compounds classes shows a similar reaction behavior for both reagents. This evidence can be used for the application of 18-MPC along with FCR for the evaluation of total content of phenols. It was established that 18-MPC is more active as an oxidizing agent with respect to phenols and for this reason in comparison with FCR the range of optimal values of pH is displaced into the more acidic region, the reaction rate is higher, and the concentration of the reagent is one order of magnitude less. It was also discovered that by using both reagents and measuring the absorbance in absorption maximum of heteropoly blue (HPB), the graduation curves were nonlinear. The observed phenomenon was explained by the changes in the composition and depth of the HPB reduction occurring when changing the ratio between the heteropoly complex and the phenol. The isobestic point present in the absorption spectra of HPBs and which was acquired from 18-MPC allows obtaining strictly linear calibration curves. By using 18-MPC the influence of reducing sugars, simple monophenols, sulphite ions, vitamins and some other compounds on the result of the determination of phenolic compounds becomes much smaller. It was shown by example of the ascorbic acid and rutin determination in the mixture that only by using 18-MPC it was possible to determine phenol and more active reducing agent separately by varying the pH of the determination. Keywords: 18-molybdophosphate heteropoly complex, Folin-Ciocalteu reagent, spectrophotometric analysis, determination of phenols.DOI: http://dx.doi.org/10.15826/analitika.2015.19.3.00