Photometric determination of niobium with azo-dyestuffs.
The azo-dyestuffs, which contain the analytically functional O,O'-dioxyazo group and are widely employed as photometric reagents for niobium, are reviewed. Two new groups of reagents are described : mono-azo-dyestuns based on R-salt and 2,7-bisazo dyestuffs based on chromotropic acid. The reaction with niobium is sensitive (epsilon = 20,000 to 40,000), selective and takes place in strongly acidic solution (0.5-6M hydrochloric or nitric acid). It is possible to extract with butanol the diphenylguanidine salt of the corresponding niobium complex and to measure the absorbance of the extract.
Alimarin
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V. I. Vemadsky Institute of Geochemistry and Analytical Chemistry U.S.S.R. Academy of Sciences, Moscow V-334, U.S.S.R.
Savvin
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SB