Cyanide spectrophotometric analysis

The ionization of certain substances, notably triarylmethyl cyanides, is promoted by light, so that spectrophotometric analysis for carbonium ions is no exception to the rule that the analyst should be alert for any parallelism between the duration of exposure to light during the analysis and the result.1 7 -1 9... 

Absorption spectrophotometric analysis procedures have been developed for a number of environmental species. For water contaminants alone, these include procedures for the determination of arsenic, boron, bromide ion, cyanide, fluoride, nitrate, phenols, phosphate, selenium, sUica, sulfide, surfactants, and tannin and lignin. A typical such procedure is the spectrophotometric determination of phenol in water by the reaction with 4-aminoantipyrene... 

In conclusion, there are a number of techniques that will give reliable results for lead analysis. The spectrophotometric method, while probably the most popular, suffers from lack of specificity, and great care must be taken to ensure that a positive test is due to lead. In addition, the technique is quite tedious, requiring several extractions and pH adjustments, and the use of cyanide solutions always poses a danger in the laboratory. The use of sulfuric acid for digestion in the procedure recommended by Rice et al. for blood and urine should be used with caution. 

Trace amounts of cyanide are usually determined by flow injection spectrophotometric procedures. The target species is first halogenated with chlora-mine-T, after which it reacts with a mixture of pyrazolone or barbituric acid and isonicotinic acid or pyridine to form a bluish-violet polymethine dye. The implementation of gas-diffusion modules in the flow setup for hydrogen cyanide separation avoids matrix interferences and enables the adaptation of inherently nonselective detectors, such as metallic silver-wire electrodes for potentiometric measurements. Total inorganic cyanide, including free and complexed species, such as iron-cyanide complexes, may be determined by sample decomposition with UV irradiation and further photometric or amperometric analysis. 

A good correlation was found between the results of the electrochemical method and those of the spectrophotometric cyanidation analysis method, which is used in clinical practice as a standardized protocol. 

M.C. Quaresma, M.F. de Carvalho, F.A. Meirelles, V.M. Santiago, R.E. SanteUi, AppUcation of hydrocyanic acid vapor generation via focused microwave radiation to the preparation of industrial effluent samples prior to free and total cyanide determinations by spectrophotometric flow injection analysis. Anal. Bioanal. Chem. 387 (2007) 1017-1025. 

The thiocyanate produced can be titrated with silver nitrate using ferric ion as an internal indicator (C. Davis and Foucar, 1912 Castigliori, 1933 Minatoya et al., 1935) or can be measured spectrophotometrically as the blood-red ferric thiocyanate complex (J. K. Bartlett and Skoog, 1954). The analysis can be performed as a potentiometric pH titration. Brom-cresol purple indicator can serve as the indicator in a titrametric method developed by Skoog and Bartlett (1955). The titration is feasible because cyanide ion is quite basic and the rate of reaction at 40°C in aqueous alcohol is large. 

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