Thiocyanate colorimetry :

The method is applied in testing the samples WO₃ containing  the concentration of 0.2~65% or little valence manganese.

The needed reagents:

1. Sodium dioxide:Na₂O₂

2. Sodium hydrate,5%

3. Potassium thiocyanate,50%

4. Stannous chloride,5%

5. Titanium trichloride,5%

6. Hydrazine sulfate

7. Sodium hypophosphite, solid

The preparation method of WO₃ standard solution as follow:

1.   Put 0.1000g tungsten trioxide into 300ml breaker, then add  50g NaOH, 200ml water, and move into 1000ml volumetric flask after dissolved, finally shake up and get WO₃ 0.1mg，100ug.

2.   Use 5% NaOH accurately dilute 10times and get 10µg tungsten trioxide per ml.

3.   Burn tungsten trioxide one hour under the temperature of 800℃.

Method description:

Use Na₂O₂ as a sample and put into the water. The hydrochloric acid is used as the medium to reduce the stannous chloride and titanium trichloride to pentavalent. Then use thiocyante to generate green –yellow tungsten acyl thiocyanate complexes. Finally, make test based on the product.

Specific procedure:

First, put 0.2~1.00g NaOH in the iron pot and add Na₂O₂，then use the glass rod to stir.

Second, heat the sample in the temperature of 750℃ until the sample melts into red fluid and take out cooling about five minutes, then put the product into 250 ~ 300ml wide mouth jar and cover the surface.

Third, stir the solution when the bottom of the jar turn into precipitation and put into 100ml volumetric flask and shake.

Finally, place the clarified or dried solution 2~10ml on the 25ml colorimetric tube or 50ml volumetric flask. Add 10ml 5% NaOH, sodium hydroxide, hydrazine sulfate and a small amount of 50% sodium hypophosphite and shake immediately. Then dilute 5%SnCl₂ solution to nearly scale, and add 5%TiCl₃ solution 1 drop with a solution of 5%SnCl₂ rushed to scale, and shake.

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