Electrogenerated bromine as a coulometric reagent for the estimation of the bioavailability of polyphenols

A method is proposed for the estimation of the bioavailability of polyphenols using electrogenerated bromine as a coulometric titrant. The titration of model solutions of casein and bovine serum albumin (BSA) shows that casein does not interact with electrogenerated bromine, while BSA reacts with the titrant in the ratio 1: 63. The proteins bind rutin and quercetin (from 14 to 90%) at a high rate and thus reduce the bioavailability of polyphenols. The concentration of free polyphenol is reduced with an increase in the concentration of protein in the mixture. The total antioxidant capacity (AOC) of tea is determined. Green tea is shown to possess higher AOC than the black one because of the partial oxidation of polyphenols to respective thearubigins and theaflavins at the fermentation step in the production of green tea. The total AOC of tea drops from 7 to 85%, in proportion to the increase in the amount of milk in the mixture. Milk proteins bind tea polyphenols into complexes because of intermolecular interactions and thus reduce their bioavailability. The observed effect of milk is independent of the brand of black tea. The degree of reduction of the total AOC of tea in going from one tea to another remains virtually constant.     

Impedimetric Detection of DNA Damage with the Sensor Based on Silver Nanoparticles and Neutral Red

Novel electrochemical DNA‐sensor based on glassy carbon electrode (GCE) modified with Ag nanoparticles, Neutral red covalently attached to its surface and native DNA adsorbed on modifier coating was developed for the estimation of DNA damage on example of model system based on Fenton reagent. As was shown, the oxidation process resulted in synchronous increase of electron transfer resistance and capacitance measured by electrochemical impedance spectroscopy (EIS). The contribution of each sensor component on the signal was specified and sensitivity estimated against similar surface coatings. The shift of EIS parameters was found to be higher than that of similar biosensors reported. The DNA sensor was tested on the estimation of antioxidant capacity of green tea infusions again the results of coulometric titration with electrogenerated bromine.     

Use of Electrogenerated Bromine for Estimating the Total Antioxidant Capacity of Plant Raw Materials and Plant-based Medicinal Preparations

Based on the results of determining individual antioxidants,electrogenerated bromine was proposed as a regent for the coulometric determination of the antioxidant capacity of aqueous and aqueous–alcoholic extracts of 35 phytopreparations.     

Discrimination of Tea by the Electrochemical Determination of its Antioxidant Properties by a Polyaniline – DNA – Polyphenazine Dye Modified Glassy Carbon Electrode

Abstract

Voltammetric sensors have been developed on the bases of polyaniline and polymeric forms of methylene blue, methylene green, and neutral red obtained by multiple cycling of the potential. The integrity of the layers and expansion of the pH range of redox activity have been achieved by intermediate adsorption of native DNA that stabilized the oxidized polyaniline form. The formation of the coating layer was confirmed by electrochemical impedance spectroscopy and scanning electron microscopy. Model oxidants (ascorbic acid, hydroquinone, and quercetin) in the concentration range from 1?×?10^?6 to 1?×?10^?3 mol L^?1 influenced the measured redox peaks of polymeric dyes with standard deviations from 2.4 to 5.5%. The peak currents were used for classification of tea brands using principal component analysis and linear discrimination analysis. The average discrimination of the tea brands purchased on local market was approximately 100%. The assessment of antioxidant properties of tea infusions was in agreement with results obtained using a coulometric bromine titration.     

薄层分离-库仑滴定法测定茄尼醇

提出以２ｍｏｌ／ＬＫＢｒ－醋酸（１：３Ｖ／Ｖ）为电液,在阳极电生溴与尼醇发生反应来测定茄尼醇含量的库仑滴定法。茄尼醇与溴反应,其ｎ值为１８,对于烟叶以物中茄尼醇,以正己烷－二氯乙烷－丙醇为展开剂,用薄层色地邓以分离,用库仑滴定法进行测定 。     

Coulometric determination of sulfur-containing amino acids using halogens as oxidizing titrants

It is found that cysteine and methionine quantitatively react with electrogenerated halogens under the conditions of galvanostatic coulometry. Cysteine reacts with all titrants, and methionine reacts only with chlorine and bromine. The stoichiometric coefficients of reactions between cysteine and halogens are 1:3, 1:3, and 1:1 for chlorine, bromine, and iodine, respectively. These coefficients for methionine reactions with chlorine and bromine are 1:2 and 1:1, respectively. It is shown that cysteine can be selectively determined in its mixtures with methionine by coulometric titration with electrogenerated iodine. It is found that twofold amounts of methionine do not interfere with the determination of cysteine. A procedure is developed for the direct coulometric determination of methionine in tablets with a relative standard deviation of 3–5%.     

The application of coulometry for total antioxidant capacity determination of human blood

New coulometric method for estimation of blood and plasma total antioxidant capacity (TAC) based on using electrogenerated bromine was proposed. TAC of blood from patients with chronic renal disease undergoing long-term hemodialysis was investigated. Statistical significant changes in TAC level of venous and arterial blood were found. Catalase activity and low density lipoproteins (LDL) concentrations were determined. Linear correlation between TAC and parameters mentioned was found. Contribution from some individual antioxidants was investigated. The developed method for TAC assay is expressive, simple, stable and reliable, and successfully could be used for TAC determination of some biological fluids. This method could be applied in clinic for estimation of blood TAC from patients.     

Bromine number determination by coulometric flow-injection titration

The bromine number, the number of grams of bromine which react with 100 grams of a substance under given conditions, is a widely used parameter in the chemical and petroleum industries. A method of performing the bromine number determination by coulometric flow-injection titration, using both sequential injection with sinusoidal flow and single zone techniques, is described. Titrations of olefins, known interfering compounds, and petroleum distillates were performed and compared with the results of conventional bromine number titrations. Analyses yielded a relative standard deviation of 2%. Results compared favorably with those obtained by the conventional method for both pure (97%) olefins and petroleum distillates. The method was found to be insensitive to interference from nitrogen compounds. The CFIT technique combines the advantages of coulometric titrations: controlled generation of reagent, avoidance of reagent standardization requirements and reagent storage and stability problems; with the advantages of FIA: small volume requirements which reduce cost and waste, controllable dilution through flow programming, toxic materials contained within a closed environment, and the capability of being automated.     

Coulometric redox titrations of some biologically active thiols with iodine in methanol and bromine in acetic acid

The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia     

Robust flow-batch coulometric/biamperometric titration system: determination of bromine index and bromine number of petrochemicals

A flow–batch system was constructed and evaluated to perform coulometric titrations with biamperometric end point detection. The flow section of the system is employed for sampling by injecting a sample volume (50–300 μL) in a flow injection-like system. About 1.5 mL of a suitable carrier solution is delivered by a peristaltic pump in order to quantitatively transfer the sample to the system titration cell (2.0 mL total inner volume). The carrier contains the coulometric precursor for the titrant species. The cell contains two pairs of platinum electrodes used for coulometric generation of reagent and biamperometric detection and is actively stirred. The titrant species is generated and the titration is performed by the usual batch procedure with the excess of titrant being detected by biamperometry following the analysis of the titration curve. System operation is computer controlled and all operations are automated, including titration curve analysis and cell cleaning after the titration is ended. The system is characterized by its robustness because its operation does not depend on flow rates, and the work using coulometric methods which generate gases at the counter-electrode is not troublesome. The flow–batch system has been evaluated for determination of bromine index and bromine number (relative to the total reactive olefin content) in petrochemicals according to an ASTM procedure. Typical precision (R.S.D.) is between 0.5 and 6% for different petrochemicals whose bromine number/index vary from 1000 to 10 mg of bromine per 100 g of sample, respectively. Recoveries for standard additions are between 92 and 123% for 10 mg of Br₂ per 100 g increments and 98 to 101% for 100 mg per 100 g increments. Accuracy of the proposed system was evaluated against results obtained by the standard ASTM with no significant difference detected at 95% confidence level.     

Simultaneous determination of platinum(II) and platinum(IV) by controlled-reagent coulometry

Both platinum(II) and the total amount of platinum were determined in the 5-μmole range with a precision of 0.3%. First, platinum(II) was determined dy oxidation with electrogenerated bromine,the equivalent quantity of electricity being measured. After reduction to platinum(II) with electrogenarated tin(II), the total amount of platinum was determined by a second oxidation with electrogenerated bromine.The reduction with tin(II) was too slow for manual control, and an electronic coulometric titrator was used.The construction of the tritator is described. The underlying coulometric principle, called controlled-reagent coulometry, and its adventages are discussed. A number of other substances were also tested.     

Galvanostatic Coulometric Determination of Aromatic Amine Derivatives in Pharmaceutical Preparations Using Electrochemically Generated Bromine

Procedures were developed for the coulometric determination of aromatic amine derivatives in model solutions and pharmaceutical preparations (anaesthesine, novocaine, novocainamide, paracetamol, streptocid, sulgin, sodium sulfacyl, ethazole, sulfadimezine, norsulfazole, and sulfamethoxazole) using electrochemically generated bromine with RSD of 1 to 5%. The stoichiometric coefficients of reactions were determined, and possible mechanisms were proposed for the reactions of bromine with the above preparations.     

Analysis of some electrochemical processes related to coulometric titrations at constant current

By considering the equilibrium potentials for the various electrode reactions which may occur in a coulometric titration, it is possible in certain cases to shorten the experimental exploratory work involved in the development of a new titration. The titration of trivalent arsenic by generated bromine and of dichromate by generated monovalent copper are treated as examples. Possible consequences of the irreversibility of electrode processes are examined. An analysis of the stability of the various chloro-complexes of mono- and di-valent copper is made in connection with the study of coulometric titrations involving generated monovalent copper     

Galvanostatic Coulometric Determination of Salicylic Acid and Some of Its Derivatives Using Electrogenerated Halogens

Reactions of electrogenerated bromine and chlorine with salicylic acid and some of its derivatives were studied. Procedures for the galvanostatic coulometric determination of 2.4 to 19.2 g/mL of salicylic, acetylsalicylic, para-aminosalicylic acids and mesalazine in model solutions and medicinal preparations with electrogenerated halogens were developed (RSD varied from 1 to 5%). The end-point of coulometric titration was determined amperometrically with two polarized platinum electrodes.     

Use of galvanostatic coulometry in the analysis of arbidol drug

Arbidol is proved to easily and completely react with electrogenerated bromine in the ratio 2: 9; so procedures for the arbidol quantification in the neat substance and drugs are developed, the RSD value does not exceed 2%. A procedure for the coulometric determination of water in the arbidol substance using the Fisher method is proposed.     

Electrochemical determination of synthetic antioxidants of bisdithiophosphonic acids

It has been found that bisdithiophosphonic acids with aryl substituents at the phosphorus atom quantitatively interact with electrogenerated halogens under the conditions of galvanostatic coulometry. Stoichiometric coefficients of the reaction between synthetic antioxidants and coulometric titrants-halogens have been determined. The corresponding reaction schemes have been proposed. The total antioxidant capacity (TAC) of the analytes has been estimated by their reaction with electrogenerated bromine. It has been demonstrated that bisdithiophosphonic acids bearing ionolic fragments demonstrate the highest TAC. It has been established that bisdithiophosphonic acids are irreversibly oxidized on a glassy carbon electrode at a potential of 800 mV with 0.1 M NaClO₄ in acetonitrile as the supporting electrolyte. The quantification limit and the analytical range of the analyte determination have been found.     

Coulometric titrations of arsenic(III) and antimony(III) with electrically generated bromine in acetic acid

Conditions for the coulometric titrations were investigated. Arsenic(III) could be titrated by continuous or discontinuous generation of bromine, and antimony(III) by discontinuous generation or back-titration. The accuracy and reproducibility depend on the pretreatment of the platinum electrodes.     

A general method for coulometric titration of alkylanilines with bromine

A general method is described for the coulometric titration of alkylanilines with anodically generated bromine. The reaction is carried out in water-acetic acid medium and the reactivity is governed by varying the water content and the concentration of bromide ion and by the addition of pyridine. In this way most types of alkylanilines can be titrated quantitatively. Unlike the case for alkylphenols, the bromine consumption is not always higher in the pyridine-containing media than in the pyridine-free. The bromine consumption is also more dependent on the bromide content of the medium than it is for alkylphenols. The mean relative error, for the best medium for each compound, is +/-0.9% for primary alkylanilines, +/-0.9% for secondary and +/-1.2% for tertiary.     

A general method for coulometric titration of alkylphenols with bromine

A general method for coulometric titration of alkylphenols with anodically generated bromine is described. The reaction is carried out in a water-acetic acid medium and the reactivity is governed by varying the water content and the concentration of bromide ion and by the addition of pyridine. In that way all types of alkylphenols can be titrated quantitatively. For phenols containing more than one free ortho and para position, the titration can also be carried out either to the monobromination stage or to the full bromination stage. The mean relative error is ± 1·2% for monobromination and ±1·5% for full bromination. A method for rapid determination of the number of free ortho and para positions in alkylphenols by using two coulometric titrations is also described.