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.

Spectrophotometric determination of vanadium after extraction as vanadium(III) picolinate.

Vanadium(V) is conveniently reduced by sodium dithionite to vanadium(III) which is extracted as its picolinate complex into chloroform. Vanadium is determined spectrophotometrically by measuring the absorbance of the complex at 385 nm against a reagent blank, Beer's law being obeyed over the range 1-50 microg/ml. The method is one of the most selective, being free from interference by relatively high concentrations of almost all the important elements, titanium, chromium, manganese, iron, cobalt, nickel, zinc, copper, aluminium, molybdenum, tungsten and uranium, found in industrial alloys.

Extractive separation and spectrophotometric determination of tungsten as phosphotungsten blue.

Phosphotungsten blue is produced by tin(II) reduction of tungstate solution complexed with phosphate at a w/w ratio of W/P = 5, in 4M hydrochloric acid medium, and extracted with isoamyl alcohol; thus tungsten is separated from Fe(III), Ni, Co, Cr(III), V(V), As(V), Sb(III), Bi, Si, U(VI), Ca and Cu(II). In presence of bismuth (0.5 mg/ml), 99.

Extractive separation of Tungsten as phosphotungstate.

Tungsten can be extracted quantitatively as phosphotungstate in micro as well as milligram concentrations by extraction with MIBK from 0.1-1M hydrochloric acid if the w/w tungsten:phosphorus ratio = 7, and separated from Fe, Ni, Co, Cr, Mn, Cu, Ca, U, Th, As, Sb, Bi and Si, after reduction of Fe(III) and cr(VI) with thiosulphate, in natural and industrial samples. Mo and V suppress the extraction of tungsten and therefore require prior separation.

Use of sulphide precipitation in separation and determination of molybdenum(V).

Molybdenum(V) is quantitatively precipitated as sulphide (99.7%) from 0.1 M At hydrochloric acid without formation of molybdenum blue and without need for a long digestion.