A Study of the Permeation of Gold(III) Through Cyanex471x Solid Supported Liquid Membranes (SSLM)

Abstract

A solid supported liquid membrane for the selective removal of Au(III) from chloride solutions has been developed by using Triisobutiphosphine sulfide (Cyanex 471x) In cumene as organic carrier. The membrane system is shown to be effective between chloride solutions ([Cl^?]= 1.0 M) containing traces of Au(III) and SCN^? 0.1 M solutions. Different kinds of at membrane supports have been studied. The results, expressed in terms of membrane permeability, show significant differences between the different supports employed, the polypropylene supports, being the most efficient.     

Nitrogen modified carbide-derived carbons as adsorbents of hydrogen sulfide

Carbide-derived carbons produced from titanium carbide at temperatures from 600 degrees C to 1000 degrees C and exhibiting different porosities were treated with urea in order to introduce nitrogen containing species to their surface. Adsorption of hydrogen sulfide in the dynamic conditions in the presence of moisture was studied on initial and modified samples. The samples, before and after exposure to hydrogen sulfide, were characterized using adsorption of nitrogen, potentiometric titration, elemental analysis, and thermal analysis. The results showed that the introduction of nitrogen significantly enhances the performance of carbons in the process of hydrogen sulfide removal. The amount adsorbed and the degree of oxidation depended on the porosity. On the samples with very small pores, the adsorption was limited, probably owing to the sterical hindrances. With an increase in the size and volume of micropores, in which water and hydrogen sulfide can be accommodated, the efficiency of H(2)S removal by CDC increased.     

Catalytic determination of selenium with a picrate-selective electrode

A method is described for the determination of selenium, based on its catalytic effect on the picrate—sulfide reaction. The determination involves a variable-time kinetic procedure using potentiometric monitoring with a picrate-selective electrode and automatic measurement of the time required for the potential to change by a preselected amount (5.0 mV). Selenium in the range 3–30 μg was determined with an average error of about 4% and relative standard deviations of about 2%. The reaction can also be followed spectrophotometrically.     

Flow-injection potentiometric determination of trace concentrations of chloride ions in low-mineralized natural waters

A procedure is developed for flow-injection potentiometric determination of trace chloride ions in low-mineralized waters and atmospheric precipitations. The procedure excludes the stage of preliminary ion-exchange concentration. The quantification limit in a 5-min analysis is 0.4 mg/L.     

Semimicrodetermination of carboxylic acids in the presence of large amounts of acyl chlorides

A procedure for the semimicrodetermination of carboxylic acids in the presence of a large excess of acyl chloride is described. Acyl chloride is first reacted with m-chloroaniline. The m-chloroaniline hydrochloride and carboxylic acid are then determined sequentially by potentiometric titration with sodium hydroxide. Titrations are performed in 80–90% p-dioxane to enhance the potentiometric breaks. With 0.05 N sodium hydroxide, as little as 0.01 mM of carboxylic acid can be determined.     

On the adsorption/oxidation of hydrogen sulfide on activated carbons at ambient temperatures

Activated carbons of various origins (bituminous coal, wood, coconut shells, and peat) were studied as adsorbents of hydrogen sulfide. Before the experiments the surface of the adsorbents was characterized by using the sorption of nitrogen, Boehm and potentiometric titrations, thermal analysis, and FTIR. The adsorbents were chosen to differ in their surface areas, pore volumes, and surface acidities. To broaden the spectrum of surface acidity, carbons were oxidized by using nitric acid and ammonium persulfate. After hydrogen sulfide adsorption the species present on the surface were analyzed using thermal analysis, ion chromatography, and elemental analysis. The H(2)S breakthrough capacity tests showed that the performances of different carbons differ significantly. For a good performance of carbons as hydrogen sulfide adsorbents a proper combination of surface chemistry of carbon and porosity is needed. It was demonstrated that a more acidic environment promotes the formation of sulfur oxides and sulfuric acid despite yielding small H(2)S removal capacities. On the other hand, a basic environment favors the formation of elemental sulfur (sulfur radicals) and yields high capacities. The presence of a sufficient amount of water preadsorbed on the carbon surface to facilitate dissociation also plays an important role in the process of H(2)S adsorption/oxidation. The results showed that there is a critical value in carbon surface acidity, which when exceeded results in a negligible hydrogen sulfide breakthrough capacity. This is consistent with the mechanism of H(2)S adsorption on unmodified carbons, where the rate-limiting step is the reaction of adsorbed hydrogen sulfide ion with dissociatively adsorbed oxygen. When the acidity is expressed as pH, its value should be higher than 5 to ensure the effective removal of hydrogen sulfide from the gas phase. Study of carbon regeneration using water washing and heat treatment showed that the adsorbents can be regenerated to about 40% of their initial capacity.     

Lower limits of the potentiometric microtitration of chloride with silver ions

The lower levels of the potentiometric titration of chloride with silver ions were investigated. The titrant was 0.001 N acetonic silver perchlorate. The titration media were acetone and acetic anhydride:acetone (4:1). A silver sulfide ion-selective indicator electrode and a double-junction reference electrode were use to monitor emf's. This titration is limited only by the trace amounts of chloride in the reagents used. Satisfactory results and well-defined titration curves were obtained down to 7 μg of chloride per 50 ml of solution (0.2 μmol; 4 × 10^?6N).A small polarization current can be used to enhance the potentiometric breaks of this titration. In an 80% methanolic medium with 0.001 N aqueous silver nitrate and a polarization current of ?0.4 μA, the lower practical limit of this titration was near 22.3 μg of chloride (1.26 × 10^?5N).     

用卡尔曼滤波作非平衡电位滴定

用长链四烷基锡为中性载体制备了性能优良的十二烷基磺酸根PVC膜电极。用其为指示电极,以非平衡方式进行快速电位滴定。借卡尔曼滤波方法可靠地确定等当点。引入的滤波算法具有通用性,能有效地节省电位滴定分析时间。     

Determination of Low Level Sulfides in Environmental Waters by Automated Gas Dialysis/Methylene Blue Colorimetry

Abstract

A sensitive and rapid automated method has been developed for the selective analysis of acid extractable sulfide in environmental samples by combining gas dialysis separation techniques with methylene blue detection procedures. Acid extractable sulfide is separated from the sample matrix by the gas dialysis membrane and subsequently trapped in a dilute sodium hydroxide receiving stream. This stream is reacted with N, N-dimethyl-p-phenylenediamine and ferric chloride to produce methylene blue which is then quantitated colorimetrically at 660 nm. For standards and nonturbid environmental samples, there is good agreement between the results obtained by this procedure and the standard methylene blue method. The effect of interferences on the accurate determination of sulfide by both methods was also examined and it was found that cupric ions significantly interfered with sulfide estimation. To obtain adequate sulfide recoveries in tap water and environmental samples ascorbic acid must be added as an antioxidant. A detection limit of 2 μg/L of sulfide has been obtained using this procedure.     

Potentiometric determination of maleic anhydride in the presence of cis-3,6-endomethylene-1,2,3,6-tetrahydrophthalic (endic) anhydride

A procedure is developed for the determination of maleic anhydride in the presence of endic anhydride by potentiometric titration in aqueous-organic solutions. It is found that separate titration of a hydrolyzed mixture of anhydrides is most efficient in the system acetonitrile-water (3 : 2).     

Surface stoichiometry of zinc sulfide and its effect on the adsorption behaviors of xanthate

ABSTRACT: In this paper, the surface stoichiometry, acid-base properties as well as the adsorption of xanthate at ZnS surfaces were studied by means of potentiometric titration, adsorption and solution speciation modeling. The surface proton binding site was determined by using Gran plot to evaluate the potentiometric titration data. Testing results implied that for stoichiometric surfaces of zinc sulfide, the proton and hydroxide determine the surface charge. For the nonstoichiometric surfaces, the surface charge is controlled by proton, hydroxide, zinc and sulfide ions depending on specific conditions. The xanthate adsorption decreases with increasing solution pH, which indicates an ion exchange reaction at the surfaces. Based on experimental results, the surface protonation, deprotonation, stoichiometry and xanthate adsorption mechanism were discussed.     

The acidimetric estimation of fluoride. A comparison of the glass with the lanthanum fluoride electrode

A rapid potentiometric titration using cerium (III) chloride as titrant with a glass electrode indicator system is proposed for fluoride estimations. The alkali fluoride (0.002-0.02 M) initially adjusted to a pH of 6.3 ± 0.05 is titrated continuously. The equivalence point is measured directly from the recorder chart as the mean of two well defined points. Calibrations are carried out with fluoride solutions of about the same salt content, or by repeating the titration on another aliquot with a standard addition of fluoride. This procedure gives results as precise as those obtained previously with the fluoride electrode without elaborate computations. A direct comparison of glass and fluoride electrode systems with different titrants is provided.     

A New Bretylium-Selective Electrode for Monitoring the Drug in Blood Serum

Abstract

We determined serum bretylium levels using a bretylium-selective electrode, constructed by incorporating sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate as an ion-exchanger and 2-fluoro-2′-nitrodiphenyl ether as a solvent mediator in a poly(vinyl chloride) membrane matrix. The detection limit was 0.4 μM and the sensitivity completely covered the bretylium concentration range (2-12 μM) required for antiarrhythmic therapy. The results correlated well with those obtained by conventional gas chromatographic analysis. The potentiometric procedure is simple, rapid, economical and, thus, useful for therapeutic drug monitoring in a clinical setting.     

Point-of-need diagnosis of cystic fibrosis using a potentiometric ion-selective electrode array

The novel approach of using a micro-sensor array of miniaturised solid-state ion-selective electrodes to analyse sweat samples for sodium, potassium and chloride simultaneously is described. The array, incorporated into a miniature flow cell which is linked to a portable PC for data acquisition, constitutes a small, portable, and simple to use analytical instrument. Samples are passed through the flow cell and over the array and an immediate potentiometric response is obtained, which can be equated to the concentrations of sodium, chloride, potassium and other parameters in the sweat sample. Used here in conjunction with a Wescor Macroduct sweat sampling unit, it promises a much simplified, much less expensive procedure for sweat analysis than the procedures currently in common use.     

A potentiometric method for the determination of uranium by stannous chloride reduction

A potentiometric method has been developed for the determination of uranium using stannous chloride as reductant. The oxidation of excess stannous chloride was accomplished with an excess of sodium nitrite, the excess of which was destroyed by sulfamic acid. The U(IV) was then determined by potentiometric titration with standard potassium dichromate. For 3–5 mg amounts of uranium the precision obtained was better than 0.3%.     

An efficient ligand-free ferric chloride catalyzed synthesis of annulated 1,4-thiazine-3-one derivatives

A straight forward route for the synthesis of coumarin-, quinolone-annulated 1,4-thiazine-3-one derivatives has been achieved by using sodium sulfide as the sulfur source and ferric chloride as catalyst in a ligand-free condition. The synthetic procedure is simple, inexpensive, and affords the products in good yields. This methodology is also applicable to naphthalene and benzene systems.     

Carbon Nanofiber and Poly[2-(methacryloyloxy) ethyl] Trimethylammonium Chloride Composite as a New Benchmark Carbon-based Electrocatalyst for Sulfide Oxidation

There is an overwhelming desire to develop new sulfide oxidation electrocatalysts that perform at low potentials and exhibit high current density for the removal and efficient sensing of sulfide. This article describes a comparative electrochemical analysis of various commercially available carbon materials and polymer/surfactant composite electrocatalysts for direct electrooxidation of sulfide in an aqueous solution. The composites were prepared from five different carbon materials multiwalled carbon nanotubes, fullerene-C₆₀, graphene, glassy carbon, and carbon nanofibers (CNF) and four different polymers: chitosan, polyvinylidene fluoride, Nafion, and indigenously synthesized poly[2-(methacryloyloxy)ethyl] trimethylammonium chloride (PMTC). The carbon@polymer composites were prepared by a simple ultrasonication technique, and the electrodes were prepared by drop-drying the prepared composite on indium tin oxide (ITO) substrates. The CNF@PMTC showed the highest positive zeta potential that allowed an accumulation of many negatively charged sulfide ions at the CNF@PMTC surface. Cyclic voltammetry was used for the electrooxidation of sulfide in an aqueous solution of tris buffer (0.05 M; pH 8.0) and KNO₃ (0.1 M). The lowest sulfide oxidation peak potential (i. e., −51 mV vs. standard hydrogen electrode) with a high catalytic current response (730 μA/cm²) of the CNF@PMTC-modified ITO electrode among the tested and previously reported carbon-based electrode materials make it ideal for direct sulfide electrooxidation. Taking this and its simple preparation method into account, CNF@PMTC can be considered a benchmark carbon-based electrocatalyst for sulfide oxidation.     

Analytical Evaluation of the Silver Sulfide Membrane Electrode

Abstract

A membrane electrode selective for sulfide and silver ion has been described. No interferences were found for sulfide ion measurements, and only mercuric ion had a measurable interference with silver ion. Other characteristics of this electrode which are evaluated include speed of response and temperature coefficients. The use of the silver sulfide membrane electrode as an end-point detector in potentiometric titrations under oxidizing conditions is illustrated.     

A novel flow-through microdialysis separation unit with integrated differential potentiometric detection for the determination of chloride in soil samples

In this paper, a novel and miniaturised flow-through dialysis-based potentiometric detector is proposed for the determination of chloride in soil samples. The outstanding feature of the designed unit is the integration of analyte isolation from matrix constituents via membrane separation with differential potentiometric detection. Two identical tubular all-solid-state Ag/AgCl ion selective electrodes (ISEs) were assembled respectively at the inlet and outlet of the acceptor channel. Thus, as a consequence of the continuous forward flow of solutions through the microdialyser the outlet tube becomes the indicator electrode for the analyte diffusate while the nested tube at the entrance serves as reference electrode. The effect of physical and chemical parameters on the mass transfer efficiency is discussed in detail and compared with conventional configurations involving downstream detection. The membrane morphology for optimum dialysis performance is also thoroughly evaluated in terms of thickness, porosity and molecular weight cut-off. Higher dialysis efficiency and reduction of dilution factors up to a value of 5 were attained by halting the recipient stream temporarily. Under the optimised conditions, a dynamic working range of 5-5000 mg l(-1) chloride with a linear interval between 10 and 5000 mg l(-1) (for 1 min stopped-flow and 200 microl sample volume), a repeatability better than 3.0% and a 3 sigma(blank) detection limit of 1.2 mg l(-1) chloride were the analytical figures of merit of the devised configuration. The potentiometric dialysis sensor features extreme tolerance to high molecular weight interfering matrix compounds (> 1000 mg l(-1) humic acid), which makes it specially suited for the interference-free potentiometric determination of chloride in soils containing high levels of organic matter. The miniature size, low-reagent consumption and high analytical throughput (25-40 h(-1)) also warrant its applicability to in-field monitoring or screening schemes. The accuracy of the measurements was assessed using ion-chromatography as an external reference method. A mean t-test showed no statistical differences between both methodologies at the 95% confidence level.     

Iodide Ion-Selective Electrode and Its Application to the Determination of Organic Compounds

The mixture of silver iodide and ferrocene is used to prepare the membrane of iodide ion-selective electrode. The interference of sulfide can be reduced by the addition of cupric ion in the test solution. Ethylene glycol is determined by potentiometric titration using iodine ion-selective electrode as an indicator electrode.