Cadmium ion selective electrode

Davey, D.E., Mulcahy, D.E., and O Connell, G.R., Flow-injection determination of phosphate with a cadmium ion-selective electrode, Talanta 37, 683,1990. 

M.N. Abbas and E. Zahran. Novel solid-state cadmium ion-selective electrodes based on its tetraiodo- and tetrabromo-ion pairs with cetylpyridinium. Journal of Electroanalytical Chemistry 576 205-213, 2005. 

Trojanowicz, M., P. W. Alexander, and D. B. Flibbert. 1998. Flow-injection potentio-metric determination of free cadmium ions with a cadmium ion-selective electrode. Anal. Chim. Acta 370 267-278. 

The quaternary ammonium salts (QAS) are widely used as ionofores of ion-selective electrodes and extractants of metals halogenic anion complexes. The influence of the QASes nature with various methyl groups contents on the cadmium extraction from bromide media has been investigated. 

Elemental composition Cd 74.74%, F 25.26%. The metal may be analyzed by various instrumental techniques (see Cadmium). Fluoride may be determined by ion chromatography or by using a fluoride ion—selective electrode. 

Elemental compostion Ce 25.56%, H 1.47%, N 20.44%, 0 52.53%. The aqueous solution of the compound may be analyzed for Ce by AA or ICP spectrophotometry. Also, the solution may be measured for NH4 ion by ammonium ion-selective electrode and the NO3 ion by nitrate ion-specific electrode, ion chromatography or cadmium-reduction colorimetry. For all these measurements, the solution may require sufficient dilutions. For quantitation, its solution may be standardized by titration with a reducing agent such as sodium oxalate in the presence of iron and ferroin indicator. 

Elemental composition Ag 63.50%, N 8.25%, O 28.25%. The salt is dissolved in water, diluted, and analyzed for silver. The nitrate ion, NO3, can be analyzed in aqueous solution by nitrate ion-selective electrode, ion chromatography, or colorimetry after reduction to NO2 ion with cadmium. The nitrate content of the salt is 36.50%. 

Elemental composition Na 27.08%, N 16.48%, 0 56.47%. An aqueous solution of the salt is analyzed for sodium by various instrumental techniques (See Sodium). Nitrate ion in solution can readily be measured by ion chromatography, nitrate-ion selective electrode, or various colorimetric methods, such as its reduction with cadmium to nitrite followed by diazotization. 

A number of Cd(II) sensors based mainly on the Ag2S/CdS mixtures [384, 385] and cadmium chelates [386] were described. Ito etal. [387] used an Ag2S/CdS ion-selective electrode for determination of cadmium ion in industrial wastewater by titration method. 

The extremely low solubility of lead phosphate in water (about 6 x 10 15m) again suggests potentiometric analysis. Selig57,59 determined micro amounts of phosphate by precipitation with lead perchlorate in aqueous medium. The sample was buffered at pH 8.25-8.75 and a lead-selective electrode was used to establish the end-point. The detection limit is about 10 pg of phosphorus. Anions which form insoluble lead salts, such as molybdate, tungstate or chromate, interfere with the procedure. Similar direct potentiometric titrations of phosphate by precipitation as insoluble salts of lanthanum(III), copper(II) or cadmium(II) are suggested, the corresponding ion-selective electrodes being used to detect the end-point. 

With metal sulphide/sUver sulphide crystal membranes, the silver ions are again the mobile species. The cadmium ion-selective crystal membrane electrode (CdS/Ag2S membrane) can be used as an example of the mechanism involved. CdS wUl be more soluble than Ag2S. The activity of the sulphide ion wiU be controUed at the interface by that of the cadmium ion ... 

A variety of methods has been described for the determination of nitrogen species (Table 4) but not all are routinely used. The cadmium reduction method is widely used in both batch and automated (continuous flow) spectrophotometric methods. In this procedure, nitrate is reduced to nitrite, which is then determined by diazotization with sulfanilamide and coupling with N-(l-naphthyl)ethylenediamine dihydrochloride (NED) to form an intensely pink-colored azo dye. This chemistry can be incorporated in a flow injection manifold to allow rapid, automated, in situ determinations in a robust and portable manner. Other common techniques for nitrogen determination are the nitrate ion-selective electrode and ion chromatography. 

Ion-selective electrodes (ISEs) are potentiometric sensors that include a selective membrane to minimize matrix interferences. The most common ISE is the pH electrode, which contains a thin glass membrane that responds to the H concentration in a solution. Other parameters that can be measured include fluoride, bromide, nitrate, and cadmium, and gases in solution such as ammonia, carbon dioxide, nitrogen oxide, and oxygen. ISEs do have their limitations including lack of selectivity and sensitivity and problems connected with conditioning of electrodes. Detection limits for nitrate-N, for example, are typically 0.098mgl for commercial field devices and have chloride as a major interferent. 

The PVC membrane electrode based on new Schiff base complexes of 2,2-[(l,3,dimethyl-l,3-propanediylidene)dini-trilojbis-benzenethiolato with Cd(II) [381] and cadmium-salen N, Ai -bis-salicyli-dene-l,2-ethylenediamine) complex [382] were used as the selective electrodes for tiocyanate ions. 

The preparation and investigation of a stable, long lived, and highly selective fast-response novel solid-state cadmium-ion electrode, based on the ion pairing... 

Chow et al. have described [407] the electrochemical sensor for cadmium ions with gold electrode modified by 3-mercap-topropionic acid followed by covalently coupling the cadmium selective hexapep-tide His-Ser-Gln-Lys-Val-Phe. 

Table 5), and several are now being used, or are potentially useful, for measuring key ocean elements. The most common use of direct potentiometry (as compared with potentiometric titrations) is for measurement of pH (Culberson, 1981). Most other cation electrodes are subject to some degree of interference from other major ions. Electrodes for sodium, potassium, calcium, and magnesium have been used successfully. Copper, cadmium, and lead electrodes in seawater have been tested, with variable success. Anion-selective electrodes for chloride, bromide, fluoride, sulfate, sulfide, and silver ions have also been tested but have not yet found wide application. 

---