Adsorption behavior of copper and cyanide ions at TiO2-solution interface

Adsorption of both copper and cyanide ions in the absence and in the presence of their complexes at TiO2-solution interfaces was investigated. The objective of this study was to demonstrate the possibility of removing heavy metal ions, exemplified by Cu(II), from aqueous solution in the presence of a ligand, e.g., CN-. Several parameters such as pH and Cu(II) and CH- ion concentration that may affect the magnitude of copper and cyanide adsorption were studied. The equilibrium of Cu-CN speciation distribution in solution and stability constant calculations have been investigated to determine the adsorption behavior of Cu(II). Results revealed that free Cu(II) ions (in the absence of CN-) were completely separated at pH8, while the adsorption of free cyanide ions, in the absence of Cu(II), reached a maximum value of 48% at pH 7. For Cu-CN complexes, the presence of CN- in excessive amount with respect to Cu(II) retarded the adsorption of Cu(II). This is attributed to the formation of multivalent anionic cyano-copper complexes such as Cu(CN)2-(3) and Cu(CN)(3-)4.     

Steady-state and flow-injection response of a metallic silver electrode for potentiometric detection of metal cyanide complex formartion

A metallic silver electrode provides a potentiometric response to Ag(I), Hg(II), Fe(III), Cu(II), Zn(II), Co(II) and Ni(II) ions, and large changes in the electrode potential of up to 400 mV are observed when these ions are injected into a 0.29 mM soulution of cyanide ion. Injection 10-μl aliquots into a reagent stream with a cyanide concentration of 0.1 mM is shown to give the expected sigmoidal-shaped response curve for peak height as a function of metal ion concentration. Sub-nanomole quantities of metal ions are detectable with a peak height of ca. 20 mV, depending on the cyanide concentration.     

Determination of cyanides by continuous distillation and flow analysis with cylindrical amperometric electrodes

A continuous system for the determination of free and complex cyanides has been developed. Hydrogen cyanide is released in an acidic solution in a counter-current system operated by a peristaltic pump, absorbed in dilute sodium hydroxide and then fed into the amperometric detector with a cylindrical silver flow-through electrode. The parameters affecting the release and absorption of cyanide, as well as the electrode response and sensitivity, are described. Differentiation between total cyanide and strongly bound metal cyanide complexes is achieved by u.v. decomposition of the complexes.     

Effect of additives on the flow-analysis determination of weak-acid-dissociable and total cyanide

The effect of reductants, complexants, and nitrite eliminators on the flow-analysis determination of weak-acid-dissociable and total cyanide has been studied for: 1. cyanide recovery from copper, nickel, and iron complexes; 2. cyanide generation from the reagents in the presence of common interferents; and 3. cyanide consumption by the reagents in the presence of those interferents. In the absence of additives the UV-assisted recovery of (total) cyanide from the iron complexes (using a succinate buffer) was insufficient. Arsenite and hypophosphite had no measurable effect on the recovery, ascorbic acid resulted in total recovery but under these conditions nitrite and sulfite seemed to destroy cyanide. Phenanthroline promoted the recovery of cyanide from iron complexes but led to formation of cyanide from thiocyanate. Citrate resulted in good recovery but in the presence of nitrite cyanide was formed; the recovery with EDTA was also good. It proved necessary to destroy nitrite by use of sulfamic acid. If a combination of EDTA, citrate, and sulfamic acid is used rather high concentrations of thiocyanate, nitrite, thiosulfate, and sulfite can be tolerated in the samples. It is strongly advisable to test modifications of the cyanide determination comprehensively, because some surprising results have been obtained.     

Enhancement of the reducing properties of metallic mercury in presence of complex forming ions

The reducing properties of metallic mercury in solutions containing ions forming precipitates or complexes with mercuric or mercurous ions have been studied.The reducing power of mercury in the presence of thiocyanate is greatly enhanced, and it is similar to that in the presence of hydrochloric acid. The effects of the thiocyanate and ferric concentrations have been examined. To reduce a 0.01 M solution of ferric ion without forming a precipitate of mercurous thiocyanate, a concentration of thiocyanate of at least 0.05 M is required. The action of mercurythiocyanate system on some oxidising substances has been studied. The most important reaction is the reduction of ferric ions. The method has been applied to the determination of iron on macro and semimicroscale and good results have been obtained.The reducing power of metallic mercury in the presence of cyanide has also been examined. In general it acts as a strong reducer in alkaline medium. Atmospheric oxygen is reduced partially to water and hydrogen peroxide. Ferricyanide is reduced quantitatively to ferrocyanide. The action of metallic mercury in the presence of cyanide on other oxidising substances has also been examined.     

The Effect of Supporting Electrolyte Concentration on Zinc Electrodeposition Kinetics from Methimazole Solutions

The kinetic parameters of Zn²⁺ ion electroreduction in sodium perchlorate used as the supporting electrolyte on the mercury electrode in the presence of methimazole were determined using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and DC polarography. The two‐stage nature of this process was demonstrated. Both steps are catalysed by a methimazole. The size of the acceleration effect depends on the concentrations of methimazole and the supporting electrolyte. The acceleration of the electrode process involves the formation of active complexes between the depolarizer ions and methimazole on the electrode surface. These complexes facilitate the exchange of charge between the electrode and zinc ions during electroreduction process. The change of the hydrating sphere of the zinc ion is also important here. This in turn depends on its oxidation state and the concentration of the supporting electrolyte.     

The effect of trace levels of cyanide on the formation of mercury-iodide complexes

The interference of trace levels of cyanide with the formation of iodo-mercury complexes is made the basis of a method of trace analysis for cyanide. The decrease in absorbance of the iodo-mercury complexes is a linear function of total cyanide concentration up to about 5 × 10⁻⁵M in 0.1M sodium hydroxide medium when the iodide and mercury total concentrations are 0.05M and 3 × 10⁻⁵M respectively. Several cyano-mercury complexes are formed simultaneously, and quite a large fraction of the cyanide remains uncomplexed.     

Amperometric method for on-line cyanide detection

An amperometric method for the detection of cyanide has been developed based on the anodic dissolution of gold in solutions containing cyanide. The method is characterized by a cyclic regeneration of the electrode surface. During the regeneration, the surface layers on the electrode are dissolved. By selection of suitable measuring potentials for the cyanide, linearity can be shown to exist between current and cyanide concentration over the concentration ranges from 0 to 10 mg/l and 10 to 100 mg/l. The lowest detection level is about 0.05 mg CN^–/l. Determinations in the concentration range investigated are possible at a measuring potential of E=270 mV. The method is suitable for detecting the end point during the decontamination of cyanide-containing sewage. The influence on the results of pH, temperature, flow rate, heavy metal content, type of decontamination agent and the presence of brighteners is discussed.     

An investigation of the deprotonation of hydrazone-based receptors on interaction with anion: develop a colorimetric system distinguishing cyanide from anions

Hydrazone-based receptors, containing fluorene-skeleton substituents, in a THF solution, in the presence of fluoride or cyanide, do not only form H-bond complexes, but mainly undergo deprotonation of the N–H fragments, an event, which is signaled by the color change, the ability of the deprotonation is associated with the fluorene skeleton. The deprotonation process is also reversible by the addition of metal ions, while cyanide from fluoride could be distinguished by the addition of copper (II).     

Lanthanide Complexes that Respond to Changes in Cyanide Concentration in Water

Cyanide ions are shown to interact with lanthanide complexes of phenacylDO3A derivatives in aqueous solution, giving rise to changes in the luminescence and NMR spectra. These changes are the consequence of cyanohydrin formation, which is favored by the coordination of the phenacyl carbonyl group to the lanthanide center. These complexes display minimal affinity for fluoride and can detect cyanide at concentrations less than 1 μm . By contrast, lanthanide complexes with DOTAM derivatives display no affinity for cyanide in water, but respond to changes in fluoride concentration.     

Potentiometric determinations with the silver sulfide membrane electrode : Part I. Determination of cyanide

The possibilities of the silver sulfide membrane electrode for the determination of cyanide are described; determinations by multiple standard addition and titration have been studied, and interferences have been checked. The determination of cyanide in solutions containing various metal complexes, and the evolution method for separation of hydrogen cyanide are discussed. Automatic titration can be used for samples containing 1 p.p.m. cyanide, and the standard addition method for 1 p.p.b. cyanide.     

Application of Tetra Cyclohexyl Tin(IV) as an Anionic Carrier for the Construction of a New Salicylate Membrane Sensor

A new tin complex namely tetracyclohexyl tin(IV) (TCHT) was synthesized and used as the ion carrier for the construction of a highly selective salicylate sensor. This sensor shows a Nernstian response to salicylate ions over a very wide concentration (1.0 × 10^?7–1.0 × 10^?1 M) in a pH range of 5.5–10.5. The optimum selectivity and response could be obtained for a membrane incorporating 30% PVC, 61% BA, 3% of cationic additive (HTAB) and 6% of TCHT. The response time of the electrode is very short in the whole concentration range (15 s). The electrode also shows an excellent discriminating ability for salicylate ions with respect to the most common organic and inorganic anions including chloride, sulfate, nitrate, nitrite, cyanide, sulfite, iodide, thiocyanate, phosphate, acetate, oxalate, citrate, and tartarate ions. The detection limit of the proposed sensor is 8.0 × 10^?8 M. The electrode was successfully used for determining the concentration of salicylate ion in synthetic serums.     

Preliminary study of nickel,ferric, lead,and copper oxinates in reactions of reextraction through the exchange of ligands: The use of chloroform solutions of the copper oxinate in the spectrophotometric determination of cyanide

In this paper a systematic study of four metallic oxinates (ferric, nickel, lead, and copper complexes) is carried out, determining some characteristics of the organic solutions of these complexes in reactions of reextraction by the exchange of ligands. These reactions are based on the decoloration produced in organic solutions of colored complexes when they are mixed with aqueous solutions of anions. The study of some characteristics and the qualitative tests shows that only the copper oxinate is interesting for quantitative purposes because its solutions in chloroform are decolored at very low concentrations of oxalate ethylenediamine tetraacetate, sulfide, and cyanide.The application of this study to the indirect spectrophotometric determination of cyanide is carried out. The decoloration varies linearly with the cyanide concentration between 10 and 50 ppm for a phase volume ratio 1:1. Finally, the error, reproducibility of the method, nature of the exchange reaction, and interferences of foreign ions are also established.     

Chemical imaging of corrosion: sum frequency generation imaging microscopy of cyanide on gold at the solid-liquid interface

Sum frequency generation (SFG) imaging is used to monitor, in situ, the reaction of cyanide ions with gold surface. Spatial and chemical variations across the surface are observed as a function of time. The initial period resulted in the formation of linearly bound cyanide to gold, and continuous exposure of gold film to cyanide solution led to the presence of higher-coordinated gold-cyanide complexes. These species were identified by their specific position in the SFG vibrational spectrum (2105, 2140, 2170, and 2225 cm(-1)). The relative amounts of these gold-cyanide species varied across the surface as resolved by SFG microscopy.     

Über die Zersetzlichkeit komplexer Metallcyanide bei der Cyanidbestimmung in Abwasser

Serial studies on the behaviour of simple and complex cyanides against the attack of dilute sulphuric acid within the determination of “total cyanide” in waste water resulted in the cyanide complexes of zinc, cadmium, copper, nickel, iron(II) and iron(III) being decomposed quite rapidly by dilute sulphuric acid in the concentration range of ≦ 100 mg CN-/l. Consequently, in such cases the total amount of cyanide can be determined in the first 25 ml of the distillate.     

Progress in the palladium-catalyzed cyanation of aryl chlorides

The development of new palladium catalysts for the cyanation of various aryl and heteroaryl chlorides is described. The combination of amine co-catalysts with chelating phosphine ligands, for example, 1,4-bis(diphenylphosphino)butane (dppb) or 1,5-bis(diphenylphosphino)pentane (dpppe), allows an efficient cyanation of chloroarenes with simple potassium cyanide. General palladium-catalyzed cyanation of nonactivated and deactivated chloroarenes is possible for the first time. Studies of the oxidative addition of aryl halides to palladium triphenylphosphine complexes in the presence and absence of amines suggest that the co-catalyst is capable of preventing catalyst deactivation caused by the presence of excess cyanide ions in solution.     

Kinetics of Gold Electrodeposition from Alkali–Cyanide Solutions: The Effect of Infinitesimal Quantities of Thallium(I) Nitrate

The effect of infinitesimal quantities of thallium ions on the gold electrodeposition from alkali–cyanide solutions is studied in conditions of a controlled time of the electrode contact with solution using the technique of renewal of the electrode surface by cutting off a thin slice of the metal. As opposed to the behavior of pure alkali–cyanide solutions, where a polarization dependence represented in the Tafel coordinates experiences an inflection, in the presence of infinitesimal quantities of thallium nitrate, no inflection is present in the curves recorded on a freshly-renewed electrode and a considerable depolarization of the process is observed. Effective values of the exchange current and the transfer coefficient increase, respectively, from values of 3 × 10^–5 A cm^–2 and 0.23 in pure alkali–cyanide solutions to 10^–4 A cm^–2 and 0.5 in the presence of thallium nitrate. It is shown that, if the potential scan is preceded by an exposure of the electrode in solution, with an increase in its duration, the depolarization effect passes through a maximum. A probable explanation for the regularities observed is suggested.     

Determination of cyanide using a microbial sensor

A microbial cyanide sensor was prepared, consisting of immobilizedSaccharomyces cerevisiae and an oxygen electrode. When the electrode was inserted into a solution containing glucose, the respiration activity of the microorganisms increased. The change in the respiration activity is monitored with the oxygen electrode. When cyanide is added to the sample solution, the electron transport chain reaction of the respiration system in the mitochondria is inhibited, resulting in a decrease in respiration. The inhibition is caused by cyanide binding with respiration enzymes such as the cytochrome oxidase complex in the mitochondrial inner membrane. Therefore, the cyanide concentration can be measured from the change in the respiration rate. When the sensor was applied to a batch system at pH 8.0 and 30°C, the cyanide calibration curve showed linearity in the concentration range between 0.3 μM and 150 μM CN-.     

The determination of free long-chain quaternary ammonium species with an ion-selective electrode based on a cetyltrimethylammonium ion pair

The cetyitrimethylammonium ion-selective electrode described is based on a tetrazole ion-pair and silicone-rubber membranes. The electrode is almost Nernstian in response from 10^-6 M to the critical micelle concentration. The electrode responds little to dodecyland decyltrimethylammonium ions and inorganic ions. Selectivity coefficients for numerous compounds are given. The uses of the ion-selective electrode are discussed in terms of the ability to monitor free quaternary ammonium ions in the presence of electrolyte and complexing additives. The electrode described can be useful in developing certain pharmaceutical formulations.     

Some analytical applications of aromatic sulfonyl haloamines: Determination of thiocyanate and cyanide ions in metal complexes and salts with bromamine-B and dichloramine-B

Simple, rapid, and reproducible methods for the determination of thiocyanate and cyanide ions in metal salts and complexes with bromamine-B (BAB) and dichloramine-B (DCB) have been developed. The oxidation involves eight and two electron changes, respectively, with NCS^? and CN^? ions in 0.05–0.20 N NaOH medium in the case of BAB and in partially aqueous medium with DCB. The proposed methods could be employed for computing the number of thiocyanate and cyanide ligands present in the respective metal complexes.