Preconcentration of trace amounts of tungsten on Amberlite XAD-7 for its spectrophotometric determination in hot spring water

A preconcentration procedure, using a short column loaded with Amberlite XAD-7, is proposed for the spectrophotometric determination of traces of tungsten. The procedure is based on the retention of tungsten on the resin after its reduction to a W(V)-thiocyanate complex with tin(II) chloride solution. Interference effects have been shown to be neglible for foreign ions including Ca²⁺, Mg²⁺, Na⁺, SO₄^2–, F^–, NO₃^–, Cu²⁺, Fe³⁺ and Mo⁶⁺. The procedure has been applied to hot spring water with satisfactory results (Recovery > 95%; relative standard deviation < 5%; relative error < 3%).