Kevser Sözgen

Due to inadequacies in analytical methodology of total antioxidant capacity (TAC) measurement, proteins are initially separated from the human serum matrix by precipitation and are left unmeasured, thereby causing an important “antioxidant gap.” The aim of this work is to measure the TAC of serum with the modified CUPric Reducing Antioxidant Capacity (CUPRAC) method, and to identify the contribution of serum proteins, especially thiol-containing proteins, to TAC. CUPRAC results were statistically compared to those found by reference methods, namely ABTS (2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid), FRAP (ferric reducing antioxidant power), and Ellman thiols assay. The curves of absorbance vs thiol concentration, as well as of absorbance vs diluted serum (whole serum, trichloroacetic acid (TCA)−precipitated and redissolved serum protein solution, and TCA supernatant fractions) volume, of three distinct serum samples showed excellent linearity and low intercept values only with the modified CUPRAC method. The proposed method will help characterize the “antioxidant gap” of serum TAC originating from protein components which should not be neglected in future antioxidant measurements.

It was aimed in this study to identify and quantify various constituents (particularly phenolics) of apple juice and to quantitatively compare the total antioxidant capacities of juices obtained from apple varieties grown in Turkey. Experimental studies were performed by ...

Poly(acrylic acid-co-methacrylamide), P(AA-co-MAAm), and poly(acrylic acid), PAA, gels were prepared and the use of these gels in the non-competitive removal of Pb2+, Cu2+, and Cd2+ ions from aqueous solutions was investigated at room temperature. Characterization of the polymers was performed by FTIR spectroscopy both before and after adsorption of metal ions on P(AA-co-MAAM) or PAA. The equilibrium swelling values (ESVs) of both polymers were determined by gravimetric method. During the adsorption of metal ions on both polymers, residual metal ion concentration in the solution (by atomic absorption spectrophotometer (AAS)) and the solution pH were measured. The kinetics of the adsorption process was determined from the experimental results. Pseudo-first and second-order plots and the correlation coefficients showed that the kinetics of non-competitive adsorption of Pb2+, Cu2+, and Cd2+ ions on P(AA-co-MAAM) or PAA is correlated best with pseudo-second-order process. While the removal order in the non-competitive adsorption of heavy metal ions on PAA was Pb2+ (2.60 mmol g−1) > Cu2+ (1.04 mmol g−1) > Cd2+ (0.88 mmol g−1), it was in the order of Pb2+ (1.85 mmol g−1) > Cd2+ (0.70 mmol g−1) > Cu2+ (0.64 mmol g−1) for P(AA-co-MAAM) copolymer. The introduction of MAAm into PAA decreased the metal ion removal capacity of copolymer for Pb2+ and Cu2+ ions considerably, but it did not significantly affect that for Cd2+ ion. Copyright © 2008 John Wiley & Sons, Ltd.

The proposed method for ascorbic acid (Vitamin C) (AA) determination is based on the oxidation of AA to dehydroascorbic acid with a Cu(II)-2,9-dimethyl-1,10-phenanthroline (neocuproine (Nc)) reagent in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450nm. This chelate was formed immediately and the apparent molar absorptivity for AA was found to be 1.60 x 10(4)dm(3)mol(-1)cm(-1). Beer's law was obeyed between 8.0 x 10(-6) and 8.0 x 10(-5)M concentration range. The relative standard deviation for 90mug AA was 3%. The Cu(II)-Nc reagent is a milder and therefore more selective oxidant than the conventional Fe(III)-1,10-phenanthroline (phen) reagent 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 otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to a number of commercial fruit juices, pharmaceutical preparations containing Vitamin C, and red wine. The meta-bisulfite content of wine was removed with an anion exchanger at pH 3 prior to analysis, and a difference extractive-spectrophotometric method of AA assay in wine was developed so as to suppress the interferences caused by wine anthocyanins and polyphenols. The findings of the developed method for fruit juices and pharmaceuticals were also statistically compared with those of HPLC so as to establish it as a reliable novel method.

The possibility of the utilization of the copper(II)-neocuproine spectrophotometric method, which has previously been shown to permit the determination of various reducing agents, to the determination of vitamin E was investigated. The molar absorptivity for vitamin E was found to be (2.1 +/- 0.1) x 10(4)l mol(-1)cm(-1) and Beer's law was obeyed between 2.4 x 10(-6) and 9.0 x 10(-5)M concentrations of alpha-tocopherol. The relative standard deviation of the slope of the absorbance vs. concentration plot was 2.1%. The results obtained by the copper(II)-neocuproine method were compared with those achieved by both the standard HPLC and the widely used iron(III)-bathophenanthroline method by means of a t-test which showed that the precision of the developed method was not essentially different from those of the others. The developed method was successfully applied to three commercial samples, two in dragée and one in ampoule form. The alpha-tocopheryl acetate contained in the samples, which did not respond directly to the Cu(II)-neocuproine reagent, was subjected to alkaline hydrolysis prior to the analysis of the hydrolysis product, i.e., alpha-tocopherol. The molar absorptivity due to Cu(I)-neocuproine at 450 nm against a reagent blank indicated a two-electron oxidation of vitamin E by Cu(II)-neocuproine, which may be slightly enhanced by solvent effects. Copper(II)-neocuproine is an oxidant of strength comparable to that of Fe(III)-bathophenanthroline. The developed method, although less sensitive, is easy to use in conventional laboratories, unlike the Fe(III)-bathophenanthroline method, which requires specially prepared reagents and solvents. The method is free from interferences from such common reductants as ascorbic acid and Fe(II) salts, found in pharmaceutical formulations, after washing the formulation with water and collecting vitamin E in the ether extract for subsequent analysis.