Fractional determination of vanadium(IV) and vanadium(V) in water samples by graphite-furnace AAS after solvent extraction with 1-butanol and 8-mercaptoquinoline

An effective separation and preconcentration method has been developed for the fractional determination of vanadium(IV) and vanadium(V) in water samples. The proposed method is based on the solvent extraction of vanadium(V) with 1-butanol (BuOH) and vanadium(IV) with 8-mercaptoquinoline (thiooxine); a preconcentration factor of 50 times is obtainable using 25 ml of a sample. A water sample was filtered through a 0.45 mum membrane filter immediately after sampling. For the determination of vanadium(IV), an aliquot of the filtered sample was subjected to the separation of vanadium(V) immediately after an adjustment of the pH to 4 with nitric acid. For determining the total vanadium, the remainder of the filtered sample was preserved by acidification to pH 1 with nitric acid. Vanadium(V) was separated into benzene by extraction with BuOH. After phase separation, dissolved BuOH in the aqueous phase was removed by evaporation in a hot water bath. The resulting solution or the acidified sample solution was subjected to the preconcentration of vanadium(IV) or total vanadium after adjusting the pH to 5.5. Both vanadium(IV) and vanadium(V) were extracted with thiooxine into chloroform, and subsequently back-extracted into 0.4 ml of a nitric acid solution. The back-extracted solution, containing 200 mug/ml of nickel as a matrix modifier, was suitable for the determination of vanadium by graphite-furnace AAS. The vanadium(V) concentration was obtained by subtracting the vanadium(IV) concentration from the total vanadium concentration. The proposed method was applied to river water samples.