The preparation and characterization of poly(acrylic acid-co-methacrylamide) gel and its use in the non-competitive heavy metal removal

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 Pb(2+), Cu(2+), and Cd(2+) 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 spectrophoto meter (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 Pb(2+), Cu(2+), and Cd(2+) 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 Pb(2+) (2.60 mmol g(-1)) > Cu(2+) (1.04 mmol g(-1)) > Cd(2+) (0.88 mmol g(-1)), it was in the order of Pb(2+) (1.85 mmol g(-1)) > Cd(2+) (0.70 mmol g(-1)) > Cu(2+) (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 Pb(2+) and Cu(2+) ions considerably, but it did not significantly affect that for Cd(2+) ion. Copyright (C) 2008 John Wiley & Sons, Ltd

High performance liquid chromatographic method with post-column detection for quantification of reducing sugars in foods

A novel liquid chromatographic analysis method with post-column detection for sugars was developed to improve existing methods in regard to operation time, selectivity, and sensitivity. This method involves separation of reducing sugars on HPLC column at 30 degrees C and 0.8 mL min(-1) flow rate, post-column reaction of sugars with Cu(II)-neocuproine (Nc) reagent at 80 degrees C and 0.3 mL min(-1) flow rate, and measurement of Cu(I)-Nc product at 450 nm. The proposed assay was applied to glucose, fructose, maltose, and lactose as reducing sugars. Non-reducing sucrose was determined indirectly, after conversion to its constitutive monomers glucose and fructose by hydrolysis, and analysis with a relative error from -2.41 to 2.09%. Honey, apple juice, and milk samples were evaluated as commercial products. The results obtained with the proposed assay compared to those of the alkaline Cu(II) -Nc reference method were found close to each other, and compatible with the label values of commercial products. The accuracy of the developed method was performed by spiking glucose to honey and lactose to milk samples using two different concentrations. The obtained recoveries with respect to the post-column HPLC method were between 97 and 105% for honey and 96-107% for milk. The method gave linear responses against sugar concentration with correlation coefficients greater than 0.996 for the four analytes (glucose, fructose, maltose and lactose) in a range of 9.0 - 342.3 mg L-1 with LOD values <= 7.4 mg L-1. With the developed method, it was possible to sensitively determine reducing sugars in various food samples at a lower temperature of post-column reaction (compared to literature values) with easy application of low cost reagents requiring minimal preliminary operation. (C) 2021 Elsevier B.V. All rights reserved

Assessment of the contributions of anthocyanins to the total antioxidant capacities of plant foods

Anthocyanins widely distributed in plant foods have antioxidant activity and several health-beneficial effects. Anthocyanin contents and their contribution to total antioxidant capacity (TAC) of various plant foods (Angeleno plum, red plum, sour cherry, red grape, beetroot, and red cabbage) were analyzed in this study by using high-performance liquid chromatography (HPLC) and spectrophotometric methods such as pH differential, cupric reducing antioxidant capacity (CUPRAC) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The individual anthocyanin constituents of plant extracts were identified and quantified by HPLC on a C-18 column using gradient elution of mobile phase comprising MeOH-0.2 % o-phosphoric acid and photodiode array detection. Trolox equivalent antioxidant capacity (TEAC) coefficients of the studied standards by the CUPRAC assay were found in the order: cyanidin > kuromanin > keracyanin > delphinidin > pelargonidin > peonidin > malvidin > peonidin-3-glucoside in accordance with the theoretical expectations of established structure-antioxidant activity relationships. The theoretical TAC values calculated by the HPLC-CUPRAC and HPLC-ABTS methods were very close to the spectrophotometric values (95-103 %) for synthetic mixtures. These combined HPLC-spectrophotometric methods using TEAC coefficients of anthocyanins determined by CUPRAC and ABTS methods become possible to evaluate the anthocyanins contribution to TAC values of foods as well as individual anthocyanins in a single chromatographic run

Spectrophotometric and Chromatographic Assessment of Contributions of Carotenoids and Chlorophylls to the Total Antioxidant Capacities of Plant Foods

Carotenoids and chlorophylls are photosynthetic compounds and also efficient antioxidants. This study aims to identify and quantify carotenoids and chlorophylls in some vegetables (carrot, tomato, spinach), to measure the total antioxidant capacity (TAG) of these samples with two spectrophotometric methods, to correlate TA C data with carotenoid structure, and to compare the TAG results with HPLC findings. Separation of the individual antioxidant pigments was achieved on a C-30 column using a developed gradient elution program involving methanol acetonitrile (50:50, v/v) with 0.1% (v/v) triethylamine (TEA) (A) and acetone (B) mobile phases. Total antioxidant capacities of the acetone extracts of studied samples, in trolox and beta-carotene equivalents, were in the order: spinach > tomato > carrot by both CUPRAC and ABTS methods. CUPRAC responded favorably to both chlorophylls a and b. The TAG calculated with aid of combined HPLC spectrophotometry was very close to the spectrophotometric value (93-108%) for real samples and synthetic mixtures

Comparison of antioxidant capacity and phenolic composition of peel and flesh of some apple varieties

BACKGROUND: Apples contain a large concentration of phenolic compounds, dependent on factors such as cultivar, harvest, storage conditions, and processing. This study aims to identify the essential phenolic compounds present in various apple varieties, to measure their total antioxidant capacity (TAC) with the CUPRAC (cupric ion reducing antioxidant capacity) and ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonate)) methods, and to correlate their TAC values with HPLC findings. RESULTS: The order of TAC (mmol Trolox g1 fresh weight) of apple peels determined with the CUPRAC method was: Granny Smith > Amasya > Sky Spur > Ervin Spur > King Luscious Arap Kizi Lutz Golden. The theoretically calculated TAC values of HPLC-quantified compounds, with the aid of the combined HPLC-CUPRAC method, accounted for 18.433.5% of the experimentally observed CUPRAC capacity of peel extracts and 19.556.3% of flesh extracts, depending on apple variety. CONCLUSION: In synthetic samples of apple antioxidants, the CUPRAC-TAC values of constituents, identified and analyzed by HPLC, proved to be additive, enabling measurement of the cooperative action of antioxidants using the proposed methodology. Apple peel showed higher contents of phenolics and therefore higher TAC than apple flesh, confirming the health benefit of the consumption of apples together with peel. (c) 2012 Society of Chemical Industr

Preparation, characterization and usage of molecularly imprinted polymer for the isolation of quercetin from hydrolyzed nettle extract

Quercetin (3,3',4',5,7-pentahydroxyflavone, QC) is a health-beneficial flavonoid, widely occurring in leaves, fruits, and flowers of various plants. In this work aiming isolation, purification and pre-concentration of QC, QC imprinted polymers (QC-MIPs) in different molar ratios {template:monomer:cross-linker (1:4:20, 1:5:30, 1:8:40, 1:10:50)} were prepared thermally through bulk polymerization by using QC as the template molecule, 4-vinylpyridine (4-VP), methacrylic acid (MAA), acrylamide (AA) as the functional monomers, ethylene glycol dimethacrylate (EDMA) as the cross-linker and 2,2'-azobisisobutyronitrile (AIBN) as initiator in the porogens of acetone and tetrahydrofuran. Their recognition and selectivity properties were investigated in solutions containing QC and other similar-structure phenolics by equilibrium binding experiments using different proportions of acetonitrile (ACN)-dimethylsulfoxide (DMSO) mixtures and methanol (MeOH) as solvents. The MIP with 1:4:20 molar ratio of QC:4-VP:EDMA was established as the most suitable for recognition of QC. Sorption parameters of the MIP and the NIP (non-imprinted polymer) were calculated by using Freundlich and Langmuir isotherms with QC solutions in ACN:DMSO (98:2, v/v). The mentioned MIP was found to be highly selective for quercetin over other phenolic compounds (rutin, catechin, etc.). Thus, molecularly imprinted solid-phase extraction (MISPE) procedures were applied for selective pre-concentration and purification of QC from synthetic mixtures of phenolic compounds and nettle extract, known as a source of official and folk medicine. The results demonstrated the possibility of direct extraction of certain pharmacophoric constituents such as QC and QC derivatives from nettle by MIP separation. (C) 2016 Elsevier B.V. All rights reserved

Determination of total antioxidant capacity of milk by CUPRAC and ABTS methods with separate characterisation of milk protein fractions

Most milk-applied antioxidant assays in literature are based on the isolation and quantification of individual antioxidative compounds, whereas total antioxidant capacity (TAC) gives a more holistic picture due to cooperative action of antioxidants. Recently, the cupric reducing antioxidant capacity (CUPRAC) method has been modified to measure the antioxidant capacities of thiol-containing proteins, where the classical ammonium acetate buffer - that may otherwise precipitate proteins-was replaced with concentrated urea buffer (able to expose embedded thiol groups of proteins to oxidative attack) adjusted to pH 7.0. Thus, antioxidant capacity of milk was investigated with two competing TAC assays, namely CUPRAC and ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonic acid))/persulphate, because only these assays were capable of evaluating protein contribution to the observed TAC value. As milk fat caused turbidity, experiments were carried out with skim milk or defatted milk samples. To determine TAC, modified CUPRAC method was applied to whole milk, separated and redissolved protein fractions, and the remaining liquid phase after necessary operations. Both TAC methods were investigated for their dilution sensitivity and antioxidant power assessment of separate milk fractions such as casein and whey. Proteins like beta-lactoglobulin and casein (but not simple thiols) exhibited enhanced CUPRAC reactivity with surfactant (SDS) addition. Addition of milk protein fractions to whole skim milk produced significant 'negative-biased' deviations (up to -26% relative standard error) from TAC absorbance additivity in the application of the ABTS method, as opposed to that of the CUPRAC method less affected by chemical deviations from Beer's law thereby producing much smaller deviations from additivity (i.e. the property of additivity is valid when the measured TAC of a mixture is equal to the sum of individual antioxidant capacities of its constituents)

PROTEIN-INCORPORATED SERUM TOTAL ANTIOXIDANT CAPACITY MEASUREMENT BY A MODIFIED CUPRAC (CUPRIC REDUCING ANTIOXIDANT CAPACITY) METHOD

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

A comprehensive review of CUPRAC methodology

Measuring the antioxidant activity/capacity levels of food and biological fluids is carried out for the meaningful comparison of the antioxidant content of foodstuffs and for the diagnosis and treatment of oxidative stress-associated diseases in clinical biochemistry. Current literature clearly states that there is no widely adopted/accepted "total antioxidant parameter" as a nutritional index available for the labeling of food and biological fluids due to the lack of standardized quantitation methods. The "parent" CUPRAC (CUPric Reducing Antioxidant Capacity) method of antioxidant measurement, introduced by our research group to world literature, is based on the absorbance measurement of Cu(I)neocuproine (Nc) chelate formed as a result of the redox reaction of chain-breaking antioxidants with the CUPRAC reagent, Cu(II)-Nc, where absorbance is recorded at the maximal light absorption wavelength of 450 nm; thus this is an electron-transfer (ET)-based method. From the parent CUPRAC method initially applied to food (apricot, herbal teas, wild edible plants, herby cheese etc.) and biological fluids (as hydrophilic and lipophilic antioxidants together or in separate fractions), a number of "daughter" methods have evolved, such as the simultaneous assay of both lipophilic and hydrophilic antioxidants in acetone-water as methyl-b-cyclodextrin inclusion complexes, determination of ascorbic acid alone in the presence of flavonoids (with preliminary extraction of flavonoids as their La(III)complexes), determination of hydroxyl radical scavenging activity of both water-soluble antioxidants (using benzoate derivatives and salicylate as hydroxylation probes) and of polyphenols using catalase to stop the Fenton reaction so as to prevent redox cycling of antioxidants, measurement of Cu(II)-catalyzed hydrogen peroxide scavenging activity and of xanthine oxidase inhibition activity of polyphenols, TAC measurement of protein thiols in urea buffer, development of a CUPRAC-based antioxidant sensor on a Nafion cation-exchanger membrane, the off-line HPLC-CUPRAC assay and finally the on-line HPLC-CUPRAC assay of antioxidants with post-column detection. The current direction of CUPRAC methodology can be best described as a self-sufficient and integrated train of measurements providing a useful "antioxidant and antiradical assay package". This review attempts to unify and summarize various methodologies of main and modified CUPRAC procedures that can normally be extracted from quite different literature sources