![Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes [An article from: Analytica Chimica Acta]](https://www.ebooknetworking.net/books/B00/0PD/bigB000PDYI8W.jpg)
Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes [An article from: Analytica Chimica Acta]
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This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2007. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.
Description:
The proposed method for ascorbic acid: AA (Vitamin C) determination is based on the oxidation of AA to dehydroascorbic acid with the CUPRAC reagent of total antioxidant capacity assay, i.e., Cu(II)-neocuproine (Nc), in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450nm. The flavonoids (essentially flavones and flavonols) normally interfering with the CUPRAC procedure were separated with preliminary extraction as their La(III) chelates into ethylacetate (EtAc). The Cu(I)-Nc chelate responsible for color development was formed immediately with AA oxidation. Beer's law was obeyed between 8.0x10^-^6 and 8.0x10^-^5M concentration range, with the equation of the linear calibration curve: A"4"5"0"n"m=1.60x10^4C (moldm^-^3)-0.0596. The relative standard deviation (R.S.D.) in the analysis of N=45 synthetic mixtures containing 1.25x10^-^2mM AA with flavonoids was 5.3%. The Cu(II)-Nc reagent is a lower redox-potential and therefore more selective oxidant than the Fe(III)-1,10-phenanthroline reagent conventionally used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that may otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to some commercial fruit juices and pharmaceutical preparations containing Vitamin C+bioflavonoids. The findings of the developed method for fruit juices and pharmaceuticals were statistically alike with those of HPLC. The proposed spectrophotometric method was practical, low-cost, rapid, and could reliably assay AA in the presence of flavonoids without enzymatic procedures open to interferences by enzyme inhibitors.
Description:
The proposed method for ascorbic acid: AA (Vitamin C) determination is based on the oxidation of AA to dehydroascorbic acid with the CUPRAC reagent of total antioxidant capacity assay, i.e., Cu(II)-neocuproine (Nc), in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450nm. The flavonoids (essentially flavones and flavonols) normally interfering with the CUPRAC procedure were separated with preliminary extraction as their La(III) chelates into ethylacetate (EtAc). The Cu(I)-Nc chelate responsible for color development was formed immediately with AA oxidation. Beer's law was obeyed between 8.0x10^-^6 and 8.0x10^-^5M concentration range, with the equation of the linear calibration curve: A"4"5"0"n"m=1.60x10^4C (moldm^-^3)-0.0596. The relative standard deviation (R.S.D.) in the analysis of N=45 synthetic mixtures containing 1.25x10^-^2mM AA with flavonoids was 5.3%. The Cu(II)-Nc reagent is a lower redox-potential and therefore more selective oxidant than the Fe(III)-1,10-phenanthroline reagent conventionally used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that may otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to some commercial fruit juices and pharmaceutical preparations containing Vitamin C+bioflavonoids. The findings of the developed method for fruit juices and pharmaceuticals were statistically alike with those of HPLC. The proposed spectrophotometric method was practical, low-cost, rapid, and could reliably assay AA in the presence of flavonoids without enzymatic procedures open to interferences by enzyme inhibitors.
