Spectrophotometry, cyanide detection

The ionic pairing reagent necessarily introduces a counterion into the system. This ion preferably should be different from any of the sample ions to be determined. Some of the most useful separations are of organic ions or ionic inorganic complexes. The separation of eight metal cyanide complexes in Fig. 9.5 would be difficult to accomplish by conventional ion chromatography. Detection in this case was by direct spectrophotometry at 214 nm. 

Complex formation in the nickel(II) - cyanide system has been investigated by spectrophotometry (267.5 nm) at 24.92°C and at several ionic strengths (/ = 0.0028 to 0.1 M) using potassium perchlorate as the ionic medium, in the pH range from 5.3 to 7.7. The nickel(II) concentration was 4 x 10 M. The [Ni ]/[CN ] ratio was varied from 0.05 to 0.8 to obtain data so that the Job s method could be applied, and othenvise kept at around A. The time required for the equilibration ranged from a few days for solutions of higher pH to several weeks for those of lower pH. Acetate and phosphate buffers were used to maintain the pH, but correction was made only to account for the formation of the acetato complex. Only formation of the complex Ni(CN)4 was detected. 

Spectrophotometry There are numerous spectropho-tometric methods for the determination of cyanide including the pyridine-benzidine method, the pyridine-pyrazole method, and the pyridine-barbituric acid method. As an example, in the latter method the pyridine-barbituric acid coupling agent produces a complex with cyanide that adsorbs principally at a wavelength of 580 nm. This method is frequently used for the measurement of airborne hydrogen cyanide in industrial air. The hydrogen cyanide is collected in an alkaline bubbler, while any particulate cyanide is collected on a prefilter. With a 31 air sample the range of quantitation is about 0.3-235 ppm ( 3-260 mgm ). In water samples, this method has a lower limit of detection of about 0.02 mg 1 . ... 

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