Electrode cyanide

Abstract. Cyanides and hydrocyanic acid are one of the priority pollutants being most toxic. Therefore, it is very important to monitor cyanide concentration with specific and sensitive analytical methods. Some analytical methods for cyanide determination were presented in the last years spectrophotometer, potentiometer with silver cyanide electrode and titrimetric method. The paper presents original results concerning the spectrometric method and argentometric titration utilization for the measurement of cyanide concentration in some distilled alcoholic drinks from plums, grapes and apricots. The obtained cyanide concentrations vary between 0.0162 and 0.0970 mg/lOOmL, being under the imposed limits. 

Figure 7.17 Dependence of the logarithm of exchange current density on the logarithm of cyanide concentration for a silver/silver cyanide electrode. The total ion concentration is kept at a concentration of 1 mol dm hy partial substitution of the KCN by KCl, and the Ag+ concentration was 5 X 10 mohdm. ...

The rate of enzymatic reaction increases with substrate concentration for example, in the case of a cyanide electrode coupled with immobilized jS-gluco-sidase enzyme, a response time of 20 s for 10 moll amygdalin and Imin for 10 " moll amygdalin is obtained. Rather than waiting until an equilibrium potential is reached, the rate of potential change (AE/At) can be measured, the result being proportional to substrate concentration. 

A new generation of solid-state cyanide electrodes, such as those based on induced co-deposition of metal chalcogenides, meet better online requirements [26]. Thus, based on these newly developed sensors. 

Metal oxide film coated metal electrodes can provide reliable potentiometric pH response. The miniaturized version of them gained application in potentiometric SECM. For example, a microdisc antimony pH electrode was used by Toth et al. [47] for investigating measuring function of silver iodide based ion selective cyanide electrode. Iridium oxide based microelectrode was applied by Wipf and coworkers [48] for pH imaging. 

Hence cyanide electrodes also exhibit slopes between 58 and 118mV/power of ten. 

The Monitor System Series 1,000 of Orion, Since the detection limit of the AgI/Ag2S cyanide electrode lies just below 0.1 mg/1, the Orion firm used a different method to indicate cyanide [351]. An Ag2S electrode is employed, which is known to indicate Ag ions down to < 10" M. A KAg(CN)2 is used as silver ion buffer to produce a definite response. The silver existing as free ions according to the equilibrium ... 

Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda-lime-silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis. 

Electroplating. Most silver-plating baths employ alkaline solutions of silver cyanide. The silver cyanide complexes that are obtained in a very low concentration of free silver ion in solution produce a much firmer deposit of silver during electroplating than solutions that contain higher concentrations. An excess of cyanide beyond that needed to form the Ag(CN)2 complex is employed to control the concentration. The silver is added to the solution either directly as silver cyanide or by oxidation of a silver-rod electrode. Plating baths frequently contain 40—140 g/L of silver cyanide... 

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

Both of these haUdes can also be determined potentiometricaHy with an appropriate ion-selective electrode. Sulfide and cyanide both interfere with the electrode response. 

The Shawinigan process uses a unique reactor system (36,37). The heart of the process is the fluohmic furnace, a fluidized bed of carbon heated to 1350—1650°C by passing an electric current between carbon electrodes immersed in the bed. Feed gas is ammonia and a hydrocarbon, preferably propane. High yield and high concentration of hydrogen cyanide in the off gas are achieved. This process is presently practiced in Spain, AustraUa, and South Africa. 

The fluohmic process is a third process for manufacturing hydrogen cyanide, which is being appHed in Spain and AustraUa. This process involves the reaction of ammonia with a hydrocarbon, usually propane or butane, in a fluidized bed of coke particles. The endothermic heat of reaction is suppHed electrically through electrodes immersed in the fluid bed. Yields from propane and ammonia are reportedly above 85% and the waste gas is essentially hydrogen, but the costs for electricity are high. Thus this process is appHcable only when there is an inexpensive source of power. 

Cyanide in Waters etc. (by Reflux Distillation followed by either Potentiometry using a Cyanide Selective Electrode or Colorimetry, or Continuous Elow Determination of Cyanide or Determination by Microdiffusion), 1988... 

Hydrogen cyanide in air Lab method using an ion-selective electrode 5612... 

Complex ions used for electroplating are anions. The cathode tends to repel them, and their transport is entirely by diffusion. Conversely, the field near the cathode assists cation transport. Complex cyanides deserve some elaboration in view of their commercial importance. It is improbable that those used are covalent co-ordination compounds, and the covalent bond breaks too slowly to accommodate the speed of electrode reactions. The electronic structure of the cyanide ion is ... 

Mercury cyanide, 5, 1062 Mercury electrodes potential range aqueous solution, 1, 480 Mercury fluoride, 5. 1059 Mercury fulminate, 2, 7, 12 5, 1063 Mercury halides, 5, 1049 Mercury iodate, 5,1068 Mercury iodide, 5. 1059 Mercury ions Hgf... 

Polynuclear transition metal cyanides such as the well-known Prussian blue and its analogues with osmium and ruthenium have been intensely studied Prussian blue films on electrodes are formed as microcrystalline materials by the electrochemical reduction of FeFe(CN)g in aqueous solutionThey show two reversible redox reactions, and due to the intense color of the single oxidation states, they appear to be candidates for electrochromic displays Ion exchange properties in the reduced state are limited to certain ions having similar ionic radii. Thus, the reversible... 

Liap, M.-S., Lu, X. and Zhang, Q.-F. (1998) Cyanide adsorbed on coinage metal electrodes A relativistic density functional investigation. International Journal of Quantum Chemistry, 67, 175-185. 

Considerable practical importance attaches to the fact that the data in Table 6.11 refer to electrode potentials which are thermodynamically reversible. There are electrode processes which are highly irreversible so that the order of ionic displacement indicated by the electromotive series becomes distorted. One condition under which this situation arises is when the dissolving metal passes into the solution as a complex anion, which dissociates to a very small extent and maintains a very low concentration of metallic cations in the solution. This mechanism explains why copper metal dissolves in potassium cyanide solution with the evolution of hydrogen. The copper in the solution is present almost entirely as cuprocyanide anions [Cu(CN)4]3, the dissociation of which by the process... 

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