I.Titration
1.Sample V:Precisely measure a 0.05-0.07g of sample and place it into a 250ml iodine flask.Add 20ml of distilled water to dissove it,and then add 20ml 0.5N KIO3,2g KI and 20ml 6N sulphuric acid to it.Allow the sample to stand for 15 minutes in a dark chamber.
2.Blank V:Add 20ml of distilled water to a 250ml iodine flask,and then add 20ml 0.5N KIO3,2g KI and 20ml 6N sulphuric acid to it.Allow the blank sample to stand for 15 minutes in a dark chamber.
3.Titrate 0.2N sodium thiosulfate to the sample and the blank respectively,which should be done quickly until the solution turns into a light yellow colour.Then,titrate 1-2ml freshly prepared starch indicator (10g/L) to them respectively until they turn colourless.Record their respective readings.
II.Water measuring method
Weigh 1-2g of sample (precise up to 0.0001g) and put it into a weighing bottle,which has been pre-dried to a constant weight in a 105°C±2°C electric oven,and then dry the sample in a 70°C±2°C electric oven for 2 hours.
The mass lost during the drying process is W2 (in %).