Determination of Total Antioxidant Capacity by a New Spectrofluorometric Method Based on Ce(IV) Reduction: Ce(III) Fluorescence Probe for CERAC Assay

A Ce(IV)-based reducing capacity (CERAC) assay was developed to measure the total antioxidant capacity (TAC) of foods, in which Ce(IV) would selectively oxidize antioxidant compounds but not citric acid and reducing sugars which are not classified as antioxidants. The method is based on the electron-transfer (ET) reaction between Ce(IV) ion and antioxidants in optimized acidic sulphate medium (i.e., 0.3 M H2SO4 and 0.7 M Na2SO4) and subsequent determination of the produced Ce(III) ions by a fluorometric method. The fluorescent product, Ce(III), exhibited strong fluorescence at 360 nm with an excitation wavelength of 256 nm, the fluorescence intensity being correlated to antioxidant power of the original sample. The linear concentration range for most antioxidants was quite wide, e.g., 5.0 x 10(-7)-1.0 x 10(-5) M for quercetin. The developed procedure was successfully applied to the TAC assay of antioxidant compounds such as trolox, quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, ferulic acid, glutathione, and cysteine. The proposed method was reproducible, additive in terms of TAC values of constituents of complex mixtures, and the trolox equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds gave good correlations with those found by reference methods such as ABTS and CUPRAC

Modified cerium(IV)-based antioxidant capacity (CERAC) assay with selectivity over citric acid and simple sugars

A Ce(IV)-based reducing capacity (CERAC) assay was developed to measure the total antioxidant capacity (TAC) of foods, in which Ce(IV) would selectively oxidize antioxidant compounds but not citric acid and reducing sugars. The redox potential of the Ce(IV) oxidant was fine-tuned in 0.3 M H2SO4 + 0.7 M Na2SO4 aqueous medium for selective oxidation. In the classical Ce(IV)-based assay for which the name CERAC was proposed, the presence of citric acid (at 1.5 x 10(-5) M) caused approximately 25% reduction in Ce(IV) (at 2.0 x 10(-4) M) recovery, whereas in the present method, the presence of citric acid (at 1.0 x 10(-4) M) caused negligible error in the TAC measurement of quercetin. The trolox equivalent antioxidant capacity (TEAC) values in the order of quercetin > rutin > gallic acid > cacatechin > caffeic acid >= ferulic acid > naringenin >= naringin > trolox >= ascorbic acid were established with the proposed method and were found to be compatible with those found with other antioxidant assays. It is noteworthy that naringin and rutin were also hydrolyzed in the acidic medium of the method so as to exert their full antioxidant capacity not measured by other TAC assays. The proposed TAC assay with Ce(IV) is simple, low-cost, rapid, and can be easily applied in modestly equipped conventional laboratories. (C) 2010 Elsevier Inc. All rights reserved

Determination of total antioxidant capacity by a new spectrophotometric method based on Ce(IV) reducing capacity measurement

Dietary antioxidants widely found in fruits and vegetables may serve the task of reducing oxidative damage in humans induced by free radicals and reactive oxygen species under 'oxidative stress' conditions. The aim of this work is to develop a simple, low-cost, sensitive, and diversely applicable indirect spectrophotometric method for the determination of total antioxidant capacity of several plants. The method is based on the oxidation of antioxidants with cerium(IV) sulfate in dilute sulfuric acid at room temperature. The Ce(IV) reducing capacity of the sample is measured under carefully adjusted conditions of oxidant concentration and pH such that only antioxidants and not other organic compounds would be oxidized. The spectrophotometric determination of the remaining Ce(IV) was performed after completion of reaction with antioxidants. Quercetin and gallic acid were used as standards for flavonoids and phenolic acids, respectively, and results of antioxidant measurements were reported as trolox equivalents. The developed procedure was successfully applied to the assay of total antioxidant capacity due to simple compounds such as trolox, quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, chlorogenic acid, ferulic acid, and p-coumaric acid, and due to phenolic acids and flavonoids in the arieal parts of nettle (Urtica Dioica L.). Blank correction of significantly absorbing plant extracts at 320 nm could be made with the aid of spectrophotometric titration. Plant selection was made in respect to high antioxidant content, and extraction was made with water. The proposed method was reproducible, and the trolox equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds were correlated to those found by reference methods such as ABTS and CUPRAC. Since the TEAC coefficients found with the proposed method of naringin-naringenin and rutin-catechin pairs were close to each other, this Ce(IV)-based assay probably caused the simultaneous hydrolysis of favonoid glycosides to the corresponding aglycones and their subsequent oxidation such that the hydrolysis products exhibed antioxidant capacities roughly proportional the number of -OH groups contained in a molecule. (c) 2006 Elsevier B.V All rights reserved

Adsorptive Removal of Methylene Blue from Simulated Dyeing Wastewater with Melamine-Formaldehyde-Urea Resin

A melamine-formaldehyde-urea (MFU) resin was used as adsorbent to clean wastewater containing a basic dye (methylene blue) used to simulate leather and textile processing dyes. Dye removal was followed by measuring the initial and final dye concentration in solution by UV-Vis spectroscopy using the analytical wavelength of lambda = 665 nm and the molar absorptivity of epsilon = (8.43 +/- 0.05) x 10(4) L mol(-1) cm(-1). The concentration range of methylene blue in solution for adsorption experiments was between 10(-7) and 10(-5) M so as to avoid dye polymerization reactions in solution that would give rise to apparent deviations from Beer's law. Batch and column methods were used for investigating adsorptive removal of dye. Parameters such as pH and contact time were optimized. The capacity of the sorbent for the dye was found by classical adsorption modeling (15.0 mg g(-1)) with the aid of a Langmuir isotherm. The optimal pH for adsorption was 7-8. Adsorption is thought to proceed mainly through cation exchange of methylene blue (MB+) with the R-COO (-) exchange groups of the sorbent. Adsorption was fast, and reached an equilibrium within 30 min. Color removal of simulated leather dyeing wastewater was shown to be feasible under optimal conditions. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 3442-3448, 200

Solid-phase extraction of Cr(VI) with magnetic melamine?formaldehyde resins, followed by its colorimetric sensing using gold nanoparticles modified with p-amino hippuric acid

A new method for magnetic solid-phase separation of trace-levels of Cr(VI) by using magnetic nanoparticles modified melamine?formaldehyde resin (Fe3O4@MFR) was described. Also, the selective and sensitive chemical optical probe was developed based on citrate-polyvinyl alcohol capped gold nanoparticle and modified with the reagent p-amino hippuric acid (PAH). Consequently, the optical probe was employed for the sensing of Cr(VI) ion in aqueous media. The sensing scheme is based on the complexation between PAH and reduced Cr(III). The linear calibration curve for Cr(VI) was calculated with preconcentration and was found in the range of 2.6?156 ?g L-1 and the limits of detection for Cr(VI) were 10.4 ?g L-1 and 2.0 ?g L-1 with the naked eye and UV?vis spectroscopic detection, respectively. More importantly, both magnetic solid-phase extraction and colorimetric optical probe are selective for detection of the target analyte. The recoveries are between 96 and 99% when exercising 15 mg of the Fe3O4@MFR. The coupled approach was employed for the pre-concentration and quantification of Cr(VI) in two real water samples (tap water and mineral water) employing the standard addition protocol