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Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes.
Anal Chim Acta. 2007 Apr 04; 588(1):88-95.AC

Abstract

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 450 nm. 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 8.0 x 10(-6) and 8.0 x 10(-5) M concentration range, with the equation of the linear calibration curve: A(450 nm)=1.60 x 10(4)C (mol dm(-3))-0.0596. The relative standard deviation (R.S.D.) in the analysis of N=45 synthetic mixtures containing 1.25 x 10(-2) mM 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.

Authors+Show Affiliations

Istanbul University, Faculty of Engineering, Chemistry Department, Avcilar, 34320 Istanbul, Turkey.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

17386797

Citation

Ozyürek, Mustafa, et al. "Spectrophotometric Determination of Ascorbic Acid By the Modified CUPRAC Method With Extractive Separation of flavonoids-La(III) Complexes." Analytica Chimica Acta, vol. 588, no. 1, 2007, pp. 88-95.
Ozyürek M, Güçlü K, Bektaşoğlu B, et al. Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes. Anal Chim Acta. 2007;588(1):88-95.
Ozyürek, M., Güçlü, K., Bektaşoğlu, B., & Apak, R. (2007). Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes. Analytica Chimica Acta, 588(1), 88-95.
Ozyürek M, et al. Spectrophotometric Determination of Ascorbic Acid By the Modified CUPRAC Method With Extractive Separation of flavonoids-La(III) Complexes. Anal Chim Acta. 2007 Apr 4;588(1):88-95. PubMed PMID: 17386797.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes. AU - Ozyürek,Mustafa, AU - Güçlü,Kubilay, AU - Bektaşoğlu,Burcu, AU - Apak,Reşat, Y1 - 2007/02/06/ PY - 2006/12/22/received PY - 2007/01/29/revised PY - 2007/01/31/accepted PY - 2007/3/28/pubmed PY - 2007/5/31/medline PY - 2007/3/28/entrez SP - 88 EP - 95 JF - Analytica chimica acta JO - Anal. Chim. Acta VL - 588 IS - 1 N2 - 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 450 nm. 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 8.0 x 10(-6) and 8.0 x 10(-5) M concentration range, with the equation of the linear calibration curve: A(450 nm)=1.60 x 10(4)C (mol dm(-3))-0.0596. The relative standard deviation (R.S.D.) in the analysis of N=45 synthetic mixtures containing 1.25 x 10(-2) mM 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. SN - 1873-4324 UR - https://www.unboundmedicine.com/medline/citation/17386797/Spectrophotometric_determination_of_ascorbic_acid_by_the_modified_CUPRAC_method_with_extractive_separation_of_flavonoids_La_III__complexes_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0003-2670(07)00272-3 DB - PRIME DP - Unbound Medicine ER -