Solid-phase spectrophotometric determination of niobium in rocks after coprecipitation with iron quinolin-8-olate

Abstract

A selective and sensitive method for the determination of niobium(v) in rocks was developed based on selective enrichment by coprecipitation and sensitive solid-phase spectrophotometric determination. In solid-phase spectrophotometry, niobium(v) was determined directly on a membrane filter as the Nbv—Sulfochlorophenol S complex fixed on the filter in the presence of zephiramine. The detection limit was 5 ng for 30 ml of sample solution. The selectivity was improved by coprecipitation using iron(III) quinolin-8-olate as a carrier precipitate (recovery >97.0%). For example, at least a 100-fold mass excess of tantalum(v) with respect to 0.3 µg of niobium(v) did not interfere in the determination. A 500-fold excess of vanadium(v) or hydrogen peroxide also did not interfere. The proposed method was applied to the determination of niobium in rock standard samples distributed by the Geological Survey of Japan. The results obtained for JB-1a, JG-1a, and JA-3 were 27.2 (27), 10.8 (12) and 3.04 (3) ppm, respectively (the proposed values are in parentheses).