Journal of Membrane Science (03767388)144(1-2)pp. 37-43
Methyl red was used as an excellent carrier for the uphill transport of Hg(II) through bulk liquid membrane. By using iodide as a metal acceptor and in the presence of sulfuric acid in receiving phase the amount of mercury transport across the bulk liquid membrane was about 90% after 180 min. By replacement of the above receiving phase with 0.45 M HCl, a simpler and more reproducible system was obtained. Oleic acid was used to overcome a minor leaching of the carrier into the aqueous phase at high acid concentration. This system was optimized with a simplex optimization program. Under optimum conditions, the amount of Hg(II) transport across the liquid membrane is about 80% after 150 min. The carrier can selectively and efficiently transport Hg2+ ion from aqueous solution containing other cations such as Cd2+, Zn2+, Cu2+, Mg2+, Ca2+, Ag+, Ni2+, Al3+, Na+, Pb2+, Fe3+ and Pd2+.
A sensitive and selective procedure is presented for the voltammetric determination of copper. The procedure involves an adsorptive accumulation of copper pyrogallol red on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of reduction current of adsorbed complex at -0.2V (vs. Ag/AgCl). The optimum conditions for the analysis of copper include pH (3.0-4.5), 20μM pyrogallol red and an accumulation potential of -0.1V (vs. Ag/AgCl). The peak current is proportional to the concentration of copper over the range 0.4-60ngml-1 with a detection limit of 0.07ngml-1 with an accumulation time of 60s. The method was applied to the determination of copper in some analytical grade salts and also in cow's liver tissue. Copyright (C) 1999 Elsevier Science B.V.
Journal of Coordination Chemistry (00958972)47(4)pp. 581-595
The dissociation and the formation rates of the Sr2+-C222 cryptate in different dimethylsulfoxide-acetonitrile mixtures have been studied spectrophotometrically using murexide as a metallochromic indicator. In all solvent mixtures used, the ratio of the rate constants for dissociation and formation of the cryptate was found to be in agreement with the formation constants obtained by an independent equilibrium spectrophotometric technique. The activation parameters Ea, ΔH‡ and ΔS‡ for the formation and dissociation of the cryptate were determined from the temperature dependence of the corresponding rate constants, and found to be strongly solvent dependent. There is a linear relationship between the logarithm of the formation constant as well as the activation parameters and the mol fraction of acetonitrile in the mixed solvent.
Journal of Membrane Science (03767388)157(2)pp. 171-176
The facilitated transport of Au(III) from cyanide solutions through a bulk liquid membrane is reported. The organic phase consisted of a chloroform solution containing Victoria blue dye as the Au(CN)-4 carrier. The effects of pH of source phase, potassium cyanide concentration in source phase, Victoria blue concentration in the organic phase and sodium hydroxide in the receiving phase on the efficiency of transport process were examined. Under optimum conditions the extent of Au(CN)-4 transport across the liquid membrane was about 97% after 180min. The carrier can selectively and efficiently transport Au(CN)-4 ion from the aqueous solutions containing other cations such as alkali and alkaline earth, Zn2+, Pb2+, Cu2+, Cd2+, Hg2+, Ag+, Co2+, Fe2+, Pt2+, Pd2+ and Ni2+. Copyright (C) 1999 Elsevier Science B.V.
A highly selective and sensitive procedure is presented for the determination of ultra-trace concentrations of molybdenum by catalytic adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the molybdenum (Mo)-methyl thymol blue (MTB) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by chlorate. Optimal analytical conditions were found to be a MTB concentration of 0.8μM, pH 2.5, a chlorate concentration of 0.5M, and an adsorption potential at 100mV versus Ag/AgCl. The peak current is proportional to the concentration of molybdenum over the range 0.01-150ngml-1 with a 3σ detection limit of 2pgml-1 with an accumulation time of 60s. The effects of possible interfering ions were studied, and it was found that the proposed procedure is free from interferences of common interfering elements such as tungsten, and iron. The procedure is applied to the determination of molybdenum in a mineral water sample and some analytical grade salts with satisfactory results. Copyright (C) 1999 Elsevier Science B.V.
Transport of Ag+ as Ag(CN)2 - ions through a bulk liquid membrane is reported. The bulk liquid membrane used is a solution of Victoria blue (VB) in chloroform. The effects of pH of the source phase, cyanide concentration in the source phase, sodium hydroxide in the receiving phase, and VB concentration in the organic phase on the efficiency of the transport system were studied. The above system has a high selectivity for Ag+ and can selectively and efficiently transport Ag(CN)2 - ion from aqueous solutions containing other cations such as alkali and alkaline earths, Zn2+, Pd2+, Cu2+, Cd2+, Hg2+, Co2+, Fe2+, Pb2+, Ni2+, and Al3+.
A technique is presented for the determination of trace amounts of copper(II) by adsorptive cathodic stripping voltammetry. The procedure is based on adsorptive accumulation of copper(II)-Alizarin Red S (ARS) complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the reduction current of the adsorbed complex at -0.16 V (vs. Ag/AgCl). The height of the copper -ARS reduction peak is linearly dependent upon the copper(II) concentration between 0.2-15 and 15-500 ng.ml-1. The detection limit of the technique is 0.05 ng.ml-1 copper(II) for a collection time of 1 minute. The method is free from most interferences. The procedure has been successfully applied to the determination of trace mounts of copper(II) in some analytical grade salts.
A highly selective and sensitive method is presented for the determination of V(IV), based on its catalytic effect on the oxidation reaction of aniline blue by bromate. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of aniline blue at 591nm, between 0.5 to 5min (the fixed time method). The effect of various parameters such as pH, concentrations of bromate and aniline blue, temperature and ionic strength on the rate of reaction were studied. The method is free from most interferences, especially from large amounts of V(V). The decrease of absorbance is proportional to the concentration of V(IV) over the entire concentration range tested (5-1200ngml-1) with a 3σ detection limit of 2.0ngml-1 and a relative standard deviation at 60-200ngml-1 V(IV) of ca. 3% (n=3).The method was applied to the determination of V(IV) in river water and some synthetic samples with satisfactory results. Copyright (C) 2000 Elsevier Science B.V.
A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of the cobalt-MTB (methyl thymol blue) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The optimum conditions for the analysis of cobalt include pH 9.0 (ammonia buffer), 2.0 μM methyl thymol blue, 0.8 M sodium nitrite and an accumulation potential of -0.5 V (versus Ag/AgCl). The peak current is proportional to the concentration of cobalt over the entire concentration range tested (0.02-500 ng ml-1) with a detection limit of 0.005 ng ml-1 for an accumulation time of 60 s. The method was applied to determination of cobalt in a mineral water sample and some analytical grade salts with satisfactory results. (C) 2000 Elsevier Science B.V.
Main Group Metal Chemistry (21910219)23(8)pp. 429-436
The dissociation rates of the Ba 2+-C222 cryptate in different dimethylsulfoxide-acetonitrile mixtures have been studied spectrophotometrically using murexide as a suitable metallochromic indicator. The activation parameters E a, ΔH ‡ and ΔS ‡ for the dissociation of the cryptate were determined from the temperature dependence of the dissociation rate constants (ka). The correlation of the dissociation rate constant with the stability constant (K s) of the barium cryptate was investigated. There is a linear relationship between log K s and the activation parameters E a, ΔH ‡ and ΔS ‡ and the mole fraction of acetonitrile in the mixed solvent.
Journal of Membrane Science (03767388)165(2)pp. 217-223
A new supported liquid membrane (SLM) system for the selective transport of zinc ion is described. The SLM used is a thin porous polyvinyldifluride membrane impregnated with dicyclohexyl-18-crown-6 dissolved in nitrophenyloctyl ether. Potassium-dicyclohexyl-18-crown-6 acts as a highly efficient carrier for the uphill transport of zinc as Zn(SCN)42- through the SLM. In the presence of L-Cysteine as a metal ion acceptor in the strip solution, transport of zinc occurs almost quantitatively after 5h. The selectivity and efficiency of zinc transport from aqueous solution containing different mixtures of Co2+, Ni2+, Cu2+, Pb2+, Cd2+, Hg2+, Fe3+ and Cr3+ ions were investigated. In the presence of citrate ion and thiourea as suitable masking agents in the feed solution, the interfering effects of Pb2+ and Cu2+ ions were completely eliminated. Copyright (C) 2000 Elsevier Science B.V.
Controlled adsorptive accumulation of bismuth (III) complexed with alizarine red S (ARS) on a hanging mercury drop electrode provides the basis for the direct stripping measurement of this element in the nanomolar concentration level. The reduction current of adsorbed complex ions of bismuth is measured by differential pulse cathodic stripping voltammetry, preceded by an accumulation period of one minute. The peak potential is at 0.05 V (vs. Ag/AgCl). Optimal experimental parameters were found to be an ARS concentration of 15 μM, an accumulation potential of -0.2 V, and an acid concentration of 0.10 M (nitric acid). The limit of detection (3σ) is 0.5 nM, and the response is linear up to 150 nM. Many common anions and cations do not interfere in the determination of bismuth. An intercomparison of bismuth determinations performed by the proposed method and previously electroanalytical methods demonstrates higher selectivity, and shorter analysis time of this method. The voltammetric procedure was then applied successfully to the determination of bismuth in various complex samples.
Iranian Journal Of Chemistry And Chemical Engineering (10219986)20(2)pp. 96-101
The reduction mechanism of molybdenum-methyl thymol blue (MTB)-chlorate system has been investigated in water on a mercury electrode. As this system is very sensitive for ultra-trace determination of molybdenum, the actual mechanism involved was studied. Electrochemical techniques, including dc fast polarography and cyclic voltammetry were employed. It is shown that, the cathodic wave of molybdenum in the presence of methyl thymol blue and chlorate has an adsorptive catalytic character.
Optical sensors have been developed for high-acidity ([H+] = 1-9 M) measurements. The indicators Rhodamine B and Safranine T were entrapped in porous silica glass films prepared by the sol-gel method. The entrapped indicators were nonleachable and respond to high acid concentrations in a reversible manner. The influences of different experimental parameters such as the catalyst concentration, the water/tetraethoxy silane ratio, the amount of co-solvent, and the amount of surfactant on the chemical and mechanical stabilities of the sol-gel films were investigated. The optical sensors possess a short response time of <5 s and are stable for a period of at least 3 months. The relative standard deviation of the absorbance measurements is <2%. The interfering effect of different alkali, alkaline earth and transition metal salts on the response behavior of the sensors was studied.
A facile supported liquid membrane (SLM) system for the selective and efficient transport of silver ion is introduced. The SLM used is a thin porous polyvinyldifluoride membrane impregnated with hexathia-18-crown-6 (HT18C6) dissolved in nitrophenyloctyl ether. HT18C6 acts as a specific carrier for the uphill transport of Ag+ ion as its picrate ion paired complex through the SLM. In the presence of thiosulfate ion as a suitable stripping agent in the strip solution, transport of silver occurs almost quantitatively after 4 h. The selectivity and efficiency of silver transport from aqueous solutions containing other Mn+ cations such as Mg2+, Ca2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, Hg2+, Fe3+ and Cr3+ ions were investigated.
International Journal of Environment and Pollution (09574352)18(2)pp. 181-189
Natural clinoptilolite-rich tuffs and natrolite from Iranian deposits and their different ion-exchanged forms were used for the adsorption of 99Mo as molybdate ion. The effect of pH, contact time, initial molybdate concentration, and some cationic and anionic interferences were also studied. To investigate the selectivity of zeolites and their exchanged forms, the isotherms of adsorption were constructed at room temperature. Desorption experiments were carried out to examine the ability of zeolite to retain adsorbed molybdate. It was concluded that molybdate could be considerably adsorbed by some of the exchanged forms of the zeolites (Ag+, Cd2+ and Pb2+ exchanged forms) whereas the uptake by the natural forms was negligible.
Journal of Radioanalytical and Nuclear Chemistry (15882780)254(3)pp. 545-550
Two natural zeolites from Iranian deposits (clinoptilolite and natrolite) were characterized and their ability for adsorption of iodide from nuclear wastewaters was evaluated. The adsorption behavior was studied on natural and modified zeolites by γ-spectrometry using 131I as radiotracer. Adsorption isotherms and distribution coefficient (Kd) were measured. The results showed that clinoptilolite is a more promising zeolite for removal of iodide compared to natrolite. Furthermore, the adsorption was higher in silver, lead and thallium forms, whereas the lowest desorption was observed in lead modified zeolite.
An electrochemical adsorptive stripping approach is presented for the trace measurement of copper. The method is based on the reduction of Cu(II) at pH 4.3 adenine (Ade) containing solution at - 90 mV (vs. SCE), adsorption of Cu-Ade complex on hanging mercury drop electrode (HMDE) and the voltammetric determination by further reduction to Cu(0) at HMDE. Experimental optimum conditions were determined in the fundamental studies. The results show that the best base solution consists of 0.05 mol L-1 acetate buffer solution (pH 4.3) and 8 × 10-6 mol L-1 adenine. For an accumulation period of 120 s, the linear range and the detection limit were found as 1.5 × 10-9 -4.5 × 10-8 mol L-1 and 5 × 10-10 mol L-1, respectively. The relative standard deviation (RSD) for determination of 1 × 10-8 mol L-1 was 5% (n = 5). The method has been applied to the analysis of copper in analytical reagent grade salts and also in cow's liver tissue with satisfactory results.
Trace amounts of thallium(I) can be determined using adsorptive cathodic stripping voltammetry in the presence of Xylenol Orange (XO). The reduction current of the thallium(I)-XO complex ion was measured by square-wave cathodic stripping voltammetry. The peak potential was at -0.44 V vs. Ag/AgCl. The effect of various parameters (pH, ligand concentration, accumulation potential and collection time) on the response are discussed. The response was linearly related to the thallium concentration in the range 0.5 - 110 ng ml-1 and 110 - 2000 ng ml-1. The limit of detection was 0.2 ng ml-1. The relative standard deviation for the determination of 80 ng ml-1 thallium was 2.8%. Many common anions and cations did not interfere with the determination of thallium. The interference of lead was reduced by the addition of 0.003 M sodium carbonate. The voltammetric procedure was then successfully applied to the determination of thallium in various complex samples.
The electrochemical properties of glutathione (GSH) monolayer on the surface of a hanging mercury drop electrode were studied. It was found that the GSH monolayer could not block out the electron transfer completely so that a multilayer built up on the electrode surface. The GSH molecules had the expansion-contraction response depending on pH value.
Potassium-decyl-18-crown-6 was used as a highly selective and efficient carrier for uphill transport of silver as AgBr2- complex ion through a chloroform bulk liquid membrane. When thiosulfate anion was used as a metal ion acceptor in the receiving phase the amounts of silver transported across the liquid membrane after 120 and 180 min were 87.0 ± 1.8% and 96.0 ± 1.9%, respectively. The selectivity and efficiency of silver transport from aqueous solution containing Cu2+, Zn2+, Ni2+, Cd2+, Pb2+ and Fe3+ ions were investigated. In the presence of EDTA at pH = 4 as suitable masking agent in the source phase, the interfering effects of Pb2+ and Fe3+ ions were diminished drastically.
Adsorption Science and Technology (02636174)21(4)pp. 373-381
The removal of radionuclides such as 129I and 131I from radioactive liquid wastes was studied. Two natural zeolites were modified with different quaternary alkylammonium ions to replace the exchangeable cations from the zeolite surface and used as adsorbent materials. The quaternary ions used for such purpose were hexadecyltrimethylammonium, tetradecyltrimethylammonium, dodecyltrimethylammonium, tetrabutylammonium and tetramethylammonium, respectively. Some of the modified forms exhibited an adsorption capacity much higher than those of the respective natural samples. In contrast, the adsorption capacity was negligible when tetrabutylammonium and tetramethylammonium ions were used. Adsorption experiments were conducted by batch and continuous experiments, and adsorption isotherms constructed from the data obtained. The effect of interfering anions on the adsorption capacity was also investigated as were the breakthrough behaviours of radioiodide in a column charged with the various adsorbents. Desorption of iodide from the modified zeolites into different solutions was also investigated. It was concluded that, in some cases, surfactant modification was an efficient process for the uptake and immobilization of iodide.
