Determination of microgram amounts of silicon in vanadium, zirconium, niobium and tantalum by molybdosilicic acid blue spectrophotometry following fluoride separation.

NAKAMURA Yoshisuke, HASEGAWA Shinichi, OKOCHI Haruno

doi:10.2116/bunsekikagaku.41.10_479

The high volatility of silicon tetrafluoride compounds was utilized to separate microgram amounts of silicon in refractory metals. After a metal sample was dissolved by strong heating in 10 ml of 50 w/v % ammonium sulfate solution and 10 ml of concentrated sulfuric acid, the solution was diluted with about 20 ml of water or 5 w/v % ammonium oxalate solution. After 0.5 w/v % sodium fluoride solution was added, the sample solution was heated on a hot plate at 70°C for 15 min to form hexafluorosilicate and then diluted to 50 ml with water or ammonium oxalate solution. A 10 ml aliquot was transferred to a generator. In order to generate silicon tetrafluoride completely without heating, the presence of about 20 ml of sulfuric acid was required. The liberated silicon tetrafluoride was carried into a solution containing boric acid by oxygen carrier gas. Then the silicon in the absorbent was determined by molybdosilicic acid blue spectrophotometry (810 nm). This method was not influenced by matrices. The recovery of silicon in each sample was more than 98 %. The relative standard deviation for the determination of 0.0008 % silicon (n = 10) in a high purity iron (JSS 002-2) was 7.1 %. The limit of detection (30- of blank) by this method was 0.76 μg, and the limit of determination (10σ of blank) was 5 ppm (m/m) for a 0.5 g of sample.

Determination of microgram amounts of silicon in vanadium, zirconium, niobium and tantalum by molybdosilicic acid blue spectrophotometry following fluoride separation.

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