New reagent for determination of molybdenum (6) and tungsten (6)

A monoazo-compound of 1-phenyl-2.3-dimethylpyrazolon-5-azo-pyrogallol (PDPAP) was synthesized and used for a spectrophotometric determination of molybdenum (6) and tungsten (4.) in their salt solutions. The reagent was synthesized from 4-antipyrine and pyrogallol and has its lambdasub(max) in the ultraviolet range (<380 nm), those of the complexes of molybdenum and tungsten are respectively 550 and 520 nm. The optimum conditions for complexing of tungsten with 1-phenyl-2.3-dimethylpyrozolon-5-azo-pyrogallon are pH 2 to 3, and the maximum absorption of the complex at pH 2 occurs at lambdasub(max)=550 nm, and at pH 3 at lambdasub(max)=520 nm. The molar coefficient of extinction for the complex under optimum conditions was determined by the saturation method, the absorption of reagents then is inadequate. The reagent and the complexes of molybdenum and tungsten are not extracted by benzene, toluene, organic alcohols, CCl4, chloroform, cyclohexane. Under optimum conditions, ions of molybdenum and tungsten form with the reagent a complex whose composition approximates Me/R=1/1, evidences that the complexes under investigation are wich monomers. The proposed reagent makes it possible to determine Mo and W in the presence of large amounts of foreign ions. The determination of molybdenum is hindered by Fe3+, W6+, Ga3+, Sc3+, Ti4+. It was found that these cations are the best masked by NaF, 8-oxyquinoline, ascorbic acid and thiourea. The determination of tungsten is hindered by Cd2+, Ti4+, Zn2+, Co2+, Mo6+, Fe2+, Fe3+, these cations are the best masked by citric acid