Cadmium titration method

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. 

Calibration solutions of cadmium and lead have been prepared from high purity (higher than 98%) cadmium and lead nitrate dissolved in nitric acid. A high accuracy titration method (EDTA complexometry reaction with photometric detection) was used to determine the final... 

The range of oxides suitable for investigations in this melt is appreciably narrowed as compared with the molten CsBr-KBr (2 1) mixture. The potentiometric titration method allows us to determine the solubilities of moderately soluble oxides in the iodide-melt, since the pO values in the section of the excess of the metal cations do not exceed 5-6. The solubility products of alkaline-earth oxides (excluding MgO), cadmium and lead oxides, were determined in Ref. [364], The values of solubility products obtained, and the derived oxide solubilities in molten Csl at 700 °C are presented in Table 3.7.15. 

The number and variety of ion-specific electrodes is rapidly increasing with no end in sight. At the present writing, it is possible to use such electrodes to determine, either by direct or indirect measurement, ionic concentrations of the following species ammonia, bromide, cadmium, calcium, chloride, cupric, cyanide, fluoride, fluoroborate, iodide, lead, nitrate, perchlorate, potassium, sulfide, sodium, sulfur dioxide, and thiocyanate, all by direct measurement, and by titration methods aluminum, boron, chromium, cobalt, magnesium, mercury, nickel, phosphate, silver, sulfate, and zinc. 

The indirect determination of certain organic substances can be made by complexometric titration methods. Such methods depend on the formation of an insoluble product between the organic material and a metal then, either the excess metal in solution is determined by a suitable titration with EDTA, or the metal-containing precipitate is decomposed and the liberated metal ions titrated. Thus, for example, narcotine, papaverine, codeine, strychnine and brucine have been determined by formation of iodobis-muthate complexes, chlorpromazine and quinine" as cadmium iodide complexes, purines and nicotinic acid derivatives by precipitation with mercury and barbiturates by precipitation with zinc. ... 

Although the most sensitive line for cadmium in the arc or spark spectmm is at 228.8 nm, the line at 326.1 nm is more convenient to use for spectroscopic detection. The limit of detection at this wavelength amounts to 0.001% cadmium with ordinary techniques and 0.00001% using specialized methods. Determination in concentrations up to 10% is accompHshed by solubilization of the sample followed by atomic absorption measurement. The range can be extended to still higher cadmium levels provided that a relative error of 0.5% is acceptable. Another quantitative analysis method is by titration at pH 10 with a standard solution of ethylenediarninetetraacetic acid (EDTA) and Eriochrome Black T indicator. Zinc interferes and therefore must first be removed. 

The complexing ability of ethylenediaminetetra-acetic acid (EDTA, H4Y) has been exploited in the coulometric titration of metal ions. The method depends on the reduction of the mercury(II) or cadmium chelate of EDTA and on the titration of the metal ion (for example, magnesium) to be determined by the anion of EDTA that is released. 

Some divalent metal ions can interfere including bariiun, cadmium, lead, manganese, strontium and zinc. These are titrated as hardness. In addition aluminum, cobalt, iron and nickel can interfere with the end point. This interference becomes more severe when phosphates are present above 10 mg k. If these metals are present at significant levels, non-EDTA methods for hardness are preferred. 

The sulfide ISE is sensitive, reliable, and useful especially in analyses of the atmosphere and waters. The nitrate ISE does not exhibit particularly good analytical properties, but it enables very fast and simple ori-entative determinations of nitrate in, e.g., waters, vegetables, and foodstuffs, which is welcome with regard to public hygiene. ISEs for various inorganic anions have somewhat lost their importance in competition with ion chromatography and those for inorganic cations often cannot compete with spectral methods nevertheless, ISEs for copper(II), lead(II), and cadmium(II) ions are sometimes useful for endpoint detection in complexometric titrations. 

The determination of glutathione by iodometric titration can be made more specific if the glutathione is selectively precipitated with cadmium lactate before analysis (3). Cysteine is first precipitated at pH 6.0 to 6.4 and then glutathione is precipitated at a pH of 6.8 to 7.0. This precipitate is separated and analyzed iodometrically. The method has been criticized on the basis of the fact that the separation is not quantitative (13). Although this method has gained some popularity in Europe it is used less frequently in this country (26, 27). 

Like zinc ions, cadmium ions can be titrated in buffered solutions with EDTA but the end-point is more easily located by high frequency titration than by an indicator. Among the instrumental methods suitable for the determination of cadmium in dilute solutions, atomic absorption is ideal and polarography is also suitable. Gravimetrically, cadmium can be precipitated as the oxinate similar to zinc. In addition, it can be precipitated as molybdate. 

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