Bromide Media Research Articles

Novel modified electrode with immobilized galvinoxyl radical for the voltammetric determination of antioxidant activity

Galvinoxyl radical (GO) immobilized on the electrode surface has been used for the voltammetric determination of antioxidant activity for the first time. Immobilization of radical on glassy carbon electrode (GCE) provides improvement of the system reversibility as well as increase of the redox currents in comparison to GO reduction in solution. But sensitivity of response is insufficient for the antioxidant activity estimation. Application of GCE modified with dispersion of CeO2 nanoparticles (NP) in cationic surfactant cetylpyridinium bromide (CPB) medium (CeO2 NP-CPB/GCE) as a base for GO immobilization provide full reversibility of its reduction (redox currents ratio of 1.02 and peak potential separation of 80 mV) and 7-fold increase of the redox currents at physiological pH of supporting electrolyte. Electrode developed has been successfully applied for the voltammetric evaluation of natural phenolics antioxidant activity expressed as the EC50 parameter (effective concentration of the antioxidant providing 50% inhibition of GO) and antioxidant activity of herbal preparations (tinctures, infusions and decoctions) as relative GO inhibition. Antioxidant activity of natural phenolics is decreased as morin > quercetin = ferulic acid > gallic acid > tannin ≈ catechin. The results obtained agree well with data of standard spectrophotometric method. The advantages of the method developed are 4-fold lower incubation time, less consumption of the reagents and the absence of limitations for colored samples.

Electrochemical recycling of waste printed circuit boards in bromide media. Part I: preliminary leaching and dismantling tests

Electrochemical recycling of waste printed circuit boards in bromide media. Part I: preliminary leaching and dismantling tests

Solid Phase Extraction and Spectrophotometric Determination of Palladium with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic Acid

A selective, sensitive, and fast procedure to determine palladium depended on the sensitive reaction of palladium(II) with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (BTAHN) coupled with solid phase extraction (CPE) of the BTAHN - Pd(II) chelate with a reversed phase polymer-based C18 cartridge was developed. In 5.0 M hydrochloric acid solution and cetyl trimethyl ammonium bromide (CTAB) medium, BTAHN reacts with palladium(II) to form a deep violet complex with a mole ratio 2:1 {BTAHN to Pd(II)}. The complex was enriched by CPE with a reversed phase polymer-based C18 cartridge. An enrichment factor of 500 was achieved by elution of the complex form the cartridge with least volume of isopentyl alcohol. Beer’s law was obeyed in the concentration range of 0.02 - 0.85 μg mL–1. The molar absorptivity of the complex was 2.61 × 105 L mol–1 cm–1 at 669 nm. The detection and quantification limits were calculated and found to be 6.3 and 19.65 ng in the original samples, respectively. For 0.4 μg mL–1 level, the relative standard deviation for eleven replicate samples was 1.06%. This procedure was successfully applied to determine palladium in environmental samples with good results.

Novel approach for the voltammetric evaluation of antioxidant activity using DPPH[rad]-modified electrode

The electrochemical behavior of 2,2-diphenyl-1-picrylhydrazyl (DPPH) immobilized on the electrode surface has been studied. Bare glassy carbon electrode (GCE) and modified with dispersions of CeO2 nanoparticles in water (CeO2-H2O/GCE) and cationic surfactant cetylpyridinium bromide medium (CeO2-CPB/GCE) has been investigated as a platform for the DPPH immobilization. The best voltammetric characteristics (peak potential separation of 70mV, system reversibility with currents ratio of 0.98 and the highest peaks currents) have been observed on CeO2-CPB/GCE. The effect of CeO2 nanoparticles concentration has been evaluated. Scanning electron microscopy and electrochemical impedance spectroscopy have been applied for the electrode characterization. DPPH/CeO2-CPB/GCE has been used for the estimation of the antioxidants activity of natural phenolic antioxidants (quercetin, tannin, catechin and ferulic acid) expressed as the EC50 parameter according to differential pulse voltammetric (DPV) data. The EC50 decreased in the following order: quercetin (29±1μM), tannin (29±4μM), catechin (117±4μM) and ferulic acid (731±17μM). These data are in a good agreement with the results of standard spectrophotometric determination. The developed approach has been successfully applied for the antioxidant activity evaluation of medicinal herbs tinctures, infusions and decoctions.

Preg-robbing of gold in chloride-bromide solution

One of the major issue in gold chloride leaching is a tendency of gold to either precipitate or adsorb on a carbonaceous matter in an ore, i.e. preg-robbing. This paper discusses issues related to a preg- robbing phenomenon in gold hydrometallurgy, specifically in gold chloride-bromide leaching. This phenomenon has been observed in the 1800s to decrease gold recovery during gold chlorination as well as the state-of-art of gold cyanidation processes. The experiments were conducted in order to study the preg- robbing phenomenon in chloride-bromide media. The tendency of preg-robbing was demonstrated by adding carbon in a non-preg-robbing ore. It was shown that the preg-robbing tendency in the chloride- bromide media was very strong. Addition of 0.01% w/w of carbon powder into the non-preg-robbing ore decreased gold recovery from 92 to 70% and addition 5% w/w of carbon decreased gold recovery to almost zero.

Detection of the Sn(III) Intermediate and the Mechanism of the Sn(IV)/Sn(II) Electroreduction Reaction in Bromide Media by Cyclic Voltammetry and Scanning Electrochemical Microscopy

Fast-scan cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) were used to investigate the reduction of Sn(IV) as the hexabromo complex ion in a 2 M HBr-4 M NaBr medium. CV at scan rates to 100 V/s and SECM indicated the reaction pathway involves ligand-coupled electron transfer via an ECEC-DISP process: (1) one-electron reduction of Sn(IV)Br6(2-) to Sn(III)Br6(3-); (2) bromide dissociation of the reduced Sn(III)Br6(3-) to Sn(III)Br5(2-); (3) disproportionation of the reduced 2Sn(III)Br5(2-) to Sn(IV)Br5(-) and Sn(II)Br5(3-); (4) one-electron reduction of Sn(III)Br5(2-) to Sn(II)Br5(3-); (5) bromide dissociation from Sn(II)Br5 to Sn(II)Br4(2-). The intermediate Sn(III) species was confirmed by SECM(3-), where the Sn(III) generated at the Au tip was collected on a Au substrate in the tip generation/substrate collection mode when the distance between the tip and substrate was a few hundred nanometers.

A fluorescent chemosensor for paeonol based on tetramethoxy resorcinarene tetraoxyacetic acid

A fluorescent chemosensor for paeonol based on tetramethoxy resorcinarene tetraoxyacetic acid (TRTA) in hexadecyltrimethylammonium bromide (CTAB) medium was investigated. The fluorescence of TRTA was quenched by paeonol due to the formation of weak fluorescent inclusion complex (Paeonol–TRTA), and the fluorescence quenching (ΔF=FTRTA−FPaeonol–TRTA) was sensitized in CTAB. Under the optimal conditions, the linear range of calibration curve for the determination of paeonol was 0.02–6.40μg/mL. The detection limit estimated and RSD was 12.05ng/mL, 2.57% (n=3, c=1.0μg/mL). The mechanism of determination was discussed by quenching type analysis, absorption spectrum titrations, Benesi–Hildebrand method, fluorescence quantum yield and IR spectra. This method has also been applied for the determination of paeonol in real sample with satisfactory result.

Carbon Nanotube Based Sensor for Simultaneous Determination of Acetaminophen and Ascorbic Acid Exploiting Multiple Response Optimization and Measures in the Presence of Surfactant

AbstractA simple procedure for the simultaneous determination of acetaminophen (AC) and ascorbic acid (AA) by differential pulse voltammetry (DPV) using a carbon nanotube paste electrode exploiting measures in cetylpyridinium bromide (CPB) medium is described. Under the best instrumental parameters of DPV, optimized by means of factorial design, the calibration plots in the range 100.0–700.0 µmol L−1 (r=0.993) and 39.4–146.3 µmol L−1 (r=0.995) with limits of detection of 7.1 and 2.1 µmol L−1, were achieved for AA and AC, respectively. The developed method was successfully applied for the AC and AA determination in pharmaceutical formulations, whose accuracy was attested by comparison with HPLC method.

Thermogalvanic effects on the corrosion of copper in heavy brine LiBr solutions

Thermogalvanic corrosion of copper in heavy brine LiBr solutions has been investigated using a zero-resistance ammeter (ZRA). The temperature gradients between copper electrodes immersed in the same LiBr solution result in the formation of thermogalvanic cells with hot anodes, leading to high and sustained thermogalvanic currents. Copper loss rates, calculated using Faraday’s law, substantially exceed 0.025mmyear−1, a value regarded as the threshold of low corrosion rates. The effects of thermogalvanic coupling on the surface properties of the anode and the cathode have been analysed by means of electrochemical impedance spectroscopy (EIS). The results obtained in this analysis have been related to the process of copper electrodissolution in bromide media.

An Efficient Synthesis of New Pyrazolines and Isoxazolines Bearing Thiazolyl and Etheral Pharmacophores

A convenient synthetic route has been developed to synthesize 5-(4-((2-phenylthiazol-4-yl) methoxy)phenyl)3-(4-sustituted phenyl)pyrazolines (5a-f) and 5-(4-((2-phenylthiazol-4-yl)methoxy)phenyl)-3-(4-substituted phenyl)isoxazolines (6a-f) starting from 2-phenyl-4-chloromethylthiazole (1). The chloromethylthiazole (1) was first condensed with 4-hydroxy benzaldehyde (2) for obtaining 4-((2-phenylthiazol-4-yl)methoxy)benzaldehyde (3). Claisen-Smidth condensation of 4-((2-phenylthiazol-4-yl)methoxy)benzaldehyde (3) and acetophenones has been carried in alkaline alcohol and obtained 3-(4-((2-phenylthiazol-4-yl)methoxy)phenyl)-1-(4substituted phenyl)prop-2-en-1-ones (4a-f). The cyclocondensation of 2-propen-1-ones has been first time carried separately with hydrazine hydrate and hydroxylamine hydrochloride in aqueous micellar tetradecyltrimethylammonium bromide (TTAB) medium for getting the titled heterocycles with good to excellent yields.

Determination of emodin by hexadecyl trimethyl ammonium bromide sensitized fluorescence quenching method of the derivatives of calix[4]arene

The fluorescence quenching effect of emodin (EMO) on the derivatives of p-tert-butyl-calix[4]arene with o-phenanthroline (TBCP) in 1.0% hexadecyl trimethyl ammonium bromide (CTAB) medium was investigated. The fluorescence of TBCP was quenched by EMO due to the formation of the weak fluorescent inclusion complex (EOM-TBCP), and the fluorescence quenching (ΔF=FTBCP–FEMO–TBCP) was sensitized in CTAB. Under the optimal conditions, the linear range of calibration curve for the determination of EMO was 1.17–23.40μg/mL. The detection limit estimated and RSD was 0.34μg/mL, 3.63% (n=3, c=4.74μg/mL). The quantum yield Yu of TBCP was approximately 2.0 times higher in the presence of CTAB than that in the absence of CTAB. The method has been applied for the determination of EMO in samples with satisfactory results.

A study on the solid phase extraction of CO(II)-IIDE chelate with C18 disk and its application to the determination of trace cobalt

A sensitive, selective and rapid method has been developed for the determination of µg l-1 level of cobalt based on the rapid reaction of cobalt(II) with isopropyl 2-[(isopropoxy carbothioyl) disulfanyl] ethanethioate chelate (IIDE) and the solid phase extraction (SPE) of the colored chelate with Waters Porapak Sep-Park C18 disk. The isopropyl 2-[(isopropoxy carbothioyl) disulfanyl]ethanethioate chelate can react with Co(II) in the presence of pH 4.2 acetic acid /sodium acetate buffer solution and cetyl trimethylammonium bromide (CTMAB) medium to form a violet chelate of a molar ratio of 1:2 (cobalt to Isopropyl 2-[(isopropoxy carbothioyl) disulfanyl]ethanethioate chelate. This chelate can be retained on Waters Porapak Sep-Park C18 disk quantitatively when they passed the disk as aqueous solution. At the end of the enrichment, the retained chelate can be eluted from the disk by 2.5 ml of ethanol (contain 5% acetic acid). In the measured solution, the molar absorptivity of the chelate was 1.58 ×/105 1 mol -1 cm-1at 635 nm, and Beer’s law was obeyed in the range of 0.01-/0.4 µg ml-1. The relative standard deviation for 11 replicate sample of 0.01 µg.ml-1 level was 2.54%. The detection limit was 0.01 µg ml-1 (in original samples). This method can be applied for the determination of µg ml-1 level of cobalt in drinking water with satisfactory results. Key words: Cobalt, solid phase extraction spectrophotometry, isopropyl 2-[(isopropoxy carbothioyl) disulfanyl] ethanethioate chelate (IIDE).

Study of the solid phase extraction and spectrophotometric determination of nickel using 5-(4′-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione in environmental samples

A rapid, sensitive and selective method for the determination of nickel based on the rapid reaction of nickel(II) with 5-(4′-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (CPAHPD) and the solid phase extraction of the Ni(II)–CPAHPD complex with C18 membrane disks has been developed. In the presence of pH 6.8 buffer solution and cetylpyridinium bromide (CPB) medium, CPAHPD reacts with nickel to form a red complex of a molar ratio of 1:1 (nickel to CPAHPD). This complex was enriched by solid phase extraction (SPE) with C18 membrane disks. An enrichment factor of 100 was obtained by elution of the complex from the disks with the minimal amount of isopentyl alcohol. The molar absorptivity and Sandell sensitivity of the complex was 3.11 × 105 L mol−1 cm−1 and 0.0189 ng cm−2, respectively at 549 nm in the measured solution. Beer's law was obeyed in the range of 0.01–0.37 μg mL−1, while that obtained by Ringbom plot was in the range of 0.025–0.35 μg mL−1. The detection and quantification limits were calculated and found to be 0.003 and 0.01 μg mL−1. The proposed method was applied to the determination of nickel in water, food, biological and soil samples with good results.

Determination of Nickel(II) by CTAB Sensitized Fluorescence Quenching Method of the Derivatives of Calix[4]arene

The fluorescence quenching effect of Ni(2+) on the derivatives of p-tert- butyl-calix[4]arene with o-phenanthroline(TBCP) was studied in cetyltrimethyl- ammonium bromide (CTAB) medium. Ni(2+) reacted with the TBCP to form inclusion complex. The fluorescence quenching was sensitized in CTAB. The linear range of calibration curve for the determination of Ni(2+) was 0.050 μg/mL ~ 1.00 μg/mL. The detection limit estimated (S/N = 3) was 5.3 ng/mL. It has been applied for the determination of Ni(II) in samples with satisfactory results.

ChemInform Abstract: Effect of Hexamethylenetetramine (HMTA) as a Corrosion Inhibitor for Copper in Bromide Medium.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalytic performance and thermostability of chloroperoxidase in reverse micelle: achievement of a catalytically favorable enzyme conformation

The catalytic performance of chloroperoxidase (CPO) in peroxidation of 2, 2'-azinobis-(-3 ethylbenzothiazoline-6-sulfononic acid) diammonium salt (ABTS) and oxidation of indole in a reverse micelle composed of surfactant-water-isooctane-pentanol was investigated and optimized in this work. Some positive results were obtained as follows: the peroxidation activity of CPO was enhanced 248% and 263%, while oxidation activity was enhanced 215% and 222% in cetyltrimethylammonium bromide (CTABr) reverse micelle medium and dodecyltrimethylammonium bromide (DTABr) medium, respectively. Thermostability was also greatly improved in reverse micelle: at 40 °C, CPO essentially lost all its activity after 5 h incubation, while 58-76% catalytic activity was retained for both reactions in the two reverse micelle media. At 50 °C, about 44-75% catalytic activity remained for both reactions in reverse micelle after 2 h compared with no observed activity in pure buffer under the same conditions. The enhancement of CPO activity was dependent mainly on the surfactant concentration and structure, organic solvent ratio (V(pentanol)/V(isooctane)), and water content in the reverse micelle. The obtained kinetic parameters showed that the catalytic turnover frequency (k(cat)) was increased in reverse micelle. Moreover, the lower K(m) and higher k(cat)/K(m) demonstrated that both the affinity and specificity of CPO to substrates were improved in reverse micelle media. Fluorescence, circular dichroism (CD) and UV-vis spectra assays indicated that a catalytically favorable conformation of enzyme was achieved in reverse micelle, including the strengthening of the protein α-helix structure, and greater exposure of the heme prosthetic group for easy access of the substrate in bulk solution. These results are promising in view of the industrial applications of this versatile biological catalyst.

Precipitation of bismuth(III) oxobromide from bromide media

Abstract—X-ray phase analysis, thermogravimetry, IR spectroscopy, and chemical analysis were used to study bismuth(III) precipitation from nitrate solutions upon addition of aqueous solutions of hydrobromic acid or ammonium bromide, and from bismuth-containing hydrobromic acid solutions. The conditions in which bismuth(III) oxobromide of BiOBr composition is formed were determined and the possibility of obtaining a high-purity product was assessed.

Kinetics of the alkaline hydrolysis of fenuron in aqueous and micellar media

AbstractThe kinetics of the hydrolysis of fenuron in sodium hydroxide has been investigated spectrometrically in an aqueous medium and in cationic micelles of cetyltrimethylammonium bromide (CTAB) medium. The reaction follows first‐order kinetics with respect to [fenuron] in both the aqueous and micellar media. The rate of hydrolysis increases with the increase in [NaOH] in the lower concentration range but shows a leveling behavior at higher concentrations. The reaction followed the rate equation, 1/kobs = 1/k + 1/(kK[OH−]), where kobs is the observed rate constant, k is rate constant in aqueous medium, and k is the equilibrium constant for the formation of hydroxide addition product. The cationic CTAB micelles enhanced the rate of hydrolytic reaction. In both aqueous and micellar pseudophases, the hydrolysis of fenuron presumably occurs via an addition–elimination mechanism in which an intermediate hydroxide addition complex is formed. The added salts decrease the rate of reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 638–644, 2007

New oscillatory phenomena during gold electrodissolution in sulfuric acid containing Br − or in concentrated HCl

In this communication, we report some new oscillatory phenomena on the electrodissolution of gold in sulfuric solution containing Br − or in concentrated HCl. It was found that gas evolution and/or liquid film can play important roles in the oscillatory electrodissolution of gold, in addition to the solid film of gold oxides as previously recognized. Oscillatory electrodissolution of gold in bromide media is given here for the first time with two cases: (i) current oscillations only with lower concentrations of bromide (0.5 M, M = mol dm −3) and sulfuric acid (0.2 M) in the narrow potential range of active–passive transition and (ii) oscillations both in potential and in current with moderate concentrations of bromide (1 M) and sulfuric acid (1 M). The depletion and replenishment of Br − surface concentration by reactions under diffusion control and by convection through periodic oxygen evolution, respectively, account for the potential oscillations. Whereas the variation of available electrode surface area results in the irregular current oscillations due to the formation–removal of liquid bromine film rather than the periodic oxygen evolution. In addition, we first show both potential and current oscillations in concentrated HCl (8 M). The depletion and replenishment of the surface Cl − concentration involving also periodic gas evolution are the main reasons for the potential oscillations like case (ii) in the Br −-containing solution. Two kinds of current oscillations were found relating the active–passive transitions (like case (i)) and the Cl − depletion–replenishment with periodic gas evolution, respectively. The current oscillations can transform from the former to the latter ones with a positive potential scan. Some preliminary explanations have been given on the mechanism of the oscillatory electrodissolution with the help of the crossed cyclic voltammagrams (CVs) and in situ Raman spectra.

Solid phase extraction and spectrophotometric determination of palladium with 2-(2-quinolylazo)-5-diethylaminobenzoic acid

A sensitive, selective and rapid method for the determination of palladium based on the rapid reaction of palladium(II) with 2-(2-quinolylazo)-5-diethylaminobenzoic acid (QADEAB) and the solid phase extraction of the Pd(II) -QADEAB chelate with a reversed phase polymer-based C18 cartridge was developed. In the presence of 0.05 - 0.5 mol/L of hydrochloric acid solution and cetyl trimethylammonium bromide (CTAB) medium QADEAB reacts with palladium(II) to form a violet complex with a mole ratio 1:2 (palladium to QADEAB). The chelate was enriched by solid phase extraction with a reversed phase polymer-based C18 cartridge. An enrichment factor of 200 was obtained by elution of the chelate form the cartridge with the minimal amount of isopentyl alcohol. The molar absorptivity of the chelate in the isopentyl alcohol medium was 1.43?105 L mol-1 cm-1 at 628 nm. Beer?s law was obeyed in the range of 0.01-1.2 ?g/mL. The relative standard deviation for eleven replicate samples at the 0.2 ?g/L level was 2.18 %. The attained detection limit amounted to 0.02 ?g/L in the original samples. This method was applied to the determination of palladium in environmental samples with good results.