Extractive separation and spectrophotometric determination of tungsten as ferrocyanide

Tungsten, in amounts ranging from micrograms to milligrams, can be extracted into isoamyl alcohol, as the tungsten(V) ferrocyanide complex obtained by reduction of tungsten(VI) with tin(II) in 4M hydrochloric acid containing ferrocyanide. It can thus be separated from iron, cobalt, chromium, manganese, arsenic, antimony, bismuth, silicon, calcium and copper, their precipitation being prevented by addition of glycerol and, in the case of iron, sulphosalicyclic acid. Molybdenum, vanadium and nickel are not separated from tungsten, however. Tungsten can also be determined spectrophotometrically as tungsten(V) ferrocyanide. The absorbance of the brown complex is measured in aqueous solution or preferably after extraction into isoamyl alcohol. As many alloying elements interfere, they should be separated by the ferrocyanide extraction or other suitable method. Both the separation and the determination methods give satisfactory results with an overall error of not more than 0.5% in the analysis of practical samples containing low or high percentages of tungsten.