Abstract
Photometric determination of 0.01 to about 5 per cent of aluminum in ferrovanadium, ferrotitanium, ferrozirconium and ferroniobium with stilbazo has been studied. The aluminum-stilbazo complex showed an absorption maximum at 495mμ with constant absorbance at pH range from 4.3 to 6.0, and Beer's law was obeyed up to 50μg of aluminum when 2.5 ml of stilbazo solution (0.08w/v%) was used. The established method is as follows. In cases of ferrovanadium and ferrotitanium, 0.1 to 0.5g of sample is decomposed by treating with hydrochloric-nitric acid. In cases of ferrozirconium and ferroniobium, samples are decomposed by treating with nitric-hydrofluoric acid, and is evaporated with sulfuric acid to strong fumes until hydrofluoric acid has been removed. After being cooled, the interfering vanadium, titanium, zirconium, niobium and iron are removed by extraction with cupferron-chloroform in the presence of 3.5 N hydrochloric acid. The acidity of the solution is adjusted to pH about 5 with ammonia water (1+1) and hydrochloric acid (1+1) using p-nitrophenol as an indicator. One ml of ascorbic acid solution (5w/v%), 10ml of the buffer solution (pH 5.60) and 2.5ml of stilbazo solution (0.08w/v%) are added, and the mixture is made up exactly to 50ml with water. The absorbance is measured at 495mμ against reagent blank.
The proposed method has advantages over the JIS method, i.e., the higher precision, the rapid and simpler procedure. The time required for an analysis is about 50 minites.
