Colorimetric Determination of Niobium with Thiocyanate

Quantitative thin layer chromatography with x-ray emission spectrometry

“…Optical stability of the ether extract was improved by addition of acetone, which should inhibit the presumed polymerization of thiocyanic acid (11).…”

“…and were recrystallized from an alcohol-water solvent. The molybdenum spray reagents for inorganic phosphates (10), and phospholipids (11), and the spray reagents and solvents for organosulfur compounds (12) were used without modification. In the solvent system for separating the inorganic phosphates on Brinkmann MN-Polygram Cel 300, isopropanol was substituted for dioxane in the solvent described by Clesceri and Lee (13).…”

Simultaneous Spectrophotometric Determination of Niobium and Tungsten. Application to Complex Alloy and Stainless Steels

“…Because small changes in the volumes of the stannous chloride-hydrochloric acid reagent and the thiocyanateacetone reagent affect the absorbance, these solutions must be added by pipet or buret. Mundy ( 17) and Freund and Levitt (7) have shown that the absorbance of a niobium-thiocyanate solution decreases with increasing amounts of sulfate. Therefore, the amount of sodium bisulfate used for fusion of the mixed oxides must be controlled within ±0.1 gram, and the duration and temperature of the fusion must be reproduced as nearly as possible, so that the concentration of sulfate or bisulfate in the final solution (0.043/) will be nearly the same in all experiments.…”

“…Niobium and tantalum will precipitate quantitatively with this method, tungsten will precipitate quantitatively if cinchonine is added {10, SO), and titanium and molybdenum may precipitate partially, depending on the composition and metallurgical history of the sample. Existing spectrophotometric methods for the determination of niobium, tantalum, and tungsten in such mixtures include reactions of niobium with hydrogen peroxide {9, 18, SI), with thiocyanate (8,4,7,(15)(16)(17), and with 8-quinolinol {13); reactions of niobium and tungsten with hydroquinone {8, 11); and reactions of tantalum with pyrogallol (2,6,11,16). All, however, are subject to interference by molybdenum, tungsten, and/ or titanium.…”

“…Marzys {15, 16) has developed a procedure for the photometric determination of niobium and tantalum in various types of ores containing titanium. This procedure combines the thiocyanate-acetone method of Freund and Levitt (7) for the determination of niobium with a modification of Dinnin's (f?) pyrogallol-hydrochloric acid method for tantalum, to enable the carrying out of both determinations on different portions of the same sample solution, with very little interference from titanium.…”