SPECTROPHOTOMETRIC DETERMINATION OF ASCORBIC ACID USING 18-MOLYBDODIPHOSPHATE IN INTENSELY COLORED JUICES
Journal Title: Вісник Одеського національного університету. Хімія - Year 2018, Vol 23, Issue 1
Abstract
A simple, selective and highly sensitive method is proposed for spectrophotometric determination of ascorbic acid in juices, which have their own intense coloration with the use of a 18-molybdodiphosphate heteropoly complex (18-MPC). If the reaction is carried out at pH <5, unlike the methods with the Folin-Chiocalteu and CUPRAC reagents, there is no interfering effect of intensely colored anthocyanins, large concentrations of sulfites, polyphenols, reducing sugars, proteins and amino acids. The absorbance is measured at a wavelength of 910 nm, which corresponds to isobestic point in the spectra of one- and twoelectron heteropoly blues that co-exist in solutions by reduction of 18-MPC. At this analytical wavelength, overlapping with anthocyanine spectra (λmax ~ 520 nm), unlike the Folin-Chiocalteu (λanal = 760 nm) and CUPRAC (λanal = 460 nm) methods, is absent. It is shown that in the presence of oxyacids a partial destruction of the heteropoly complex occurs and the reaction time of the 18-MPC reduction increases but the stability of the formed heteropoly blue does not affected. To reduce the negative effects of oxyacids, it is recommended to dilute the analyzed solutions and increase the concentration of the reagent. The calibration graph for the determination of ascorbic acid in the presence of oxyacids, constructed at a wavelength of 910 nm and a reaction time of 30 minutes, is linear in the range of concentrations from10 μmol / l to 0.1 mmol / l. The method was applied for the analysis of freshly prepared dogwood, grass, red currant, beet and commercially available juices of black currant and pomegranate juices. The content of ascorbic acid in these assay objects determined by means of 18-molybdodiphosphate is in good agreement with the contents found in the literature, as well as with the results obtained by the voltammetric method in the case of pomegranate juice.
Authors and Affiliations
T. A. Denisenko, Yu. V. Miekh, А. B. Vishnikin
Keywords
Related Articles
- EP ID EP493647
- DOI 10.18524/2304-0947.2018.1(65).122837
- Views 43
- Downloads 0
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