Extractive spectrophotometric determination of niobium in pyrochlore-bearing rocks with 5,7-dichloroquinolin-8-ol

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Abstract
A spectrophotometric method for the determination of trace amounts of niobium(V) based on its extraction into chloroform with 5,7-dichloroquinolin-8-ol from a hydrochloric acid medium has been developed. The maximum absorbance of the extracted species occurs at 400 nm, the molar absorptivity being (1.28 ± 0.02)× 104 l mol–1 cm–1. Beer's law is obeyed over the range 10–80 µg of niobium(V) extracted. The relative standard deviation is 0.92% and the recovery of niobium is 99.6 ± 0.5%. The method is particularly suitable for the determination of niobium in ores and rocks, as commonly interfering elements present in niobium ores did not interfere in this determination. Results of the successful analysis of standard and synthetic niobium ores with niobium contents ranging from 0.1 to 1.0% are given. A useful modification of Faye's method for dissolution of niobium ores is reported. The special characteristics and importance of drying the organic phase in the spectrophotometric measurements are discussed.

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