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Chemex (lake and stream sediment) COL(W)
Chemex, lake and stream sediment; colourimetry (tungsten)
Tungsten was determined as follows: A 0.2 g sample of sediment was fused with 1g K2S2O7 in a rimless test tube at 575oC for 15 minutes in a furnace. The cooled melt was then leached with 10 ml concentrated HCl in a water bath heated to 85oC. After the soluble material had completely dissolved, the insoluble material was allowed to settle and an aliquot of 5 ml was transferred to another test tube. 5 ml of 20% SnCl2 soution were then added to the sample aliquot, mixed and heated for 10 minutes at 85oC in a hot water bath. A 1 ml aliquot of dithiol solution (1% dithiol in iso-amyl acetate) was added to the test solution and the test solution was heated for 4 - 6 hours at 80 - 85oC in a hot water bath. The test solution was then removed from the hot water bath, cooled and 2.5 ml of kerosene added to dissolve the globule containing the tungsten-dithiol complex. The colour intensity of the kerosene solution was measured at 630 nm using a spectrophotometer. The method is described by Quin and Brooks (1972).
Quin, B.F. and Brooks, R.R. (1972). The rapid determination of tungsten in soils, stream sediments, rocks and vegetation. Analytica Chimica Acta v58 p301-309.
Sample material: solid
Sample weight: 200 milligrams
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