Assay

Introduce 0.250 g to 1.000 g of the substance to be examined, according to the vinyl acetate content of the copolymer to be examined, into a 300 ml conical flask with a ground-glass neck containing a magnetic stirrer. Add 40 ml of xylene R. Boil under a reflux condenser with stirring for 4 h. Stirring continuously, allow to cool until precipitation begins before slowly adding 25.0 ml of alcoholic potassium hydroxide solution R1. Boil again under a reflux condenser with stirring for 3 h. Allow to cool with continued stirring, rinse the condenser with 50 ml of water R and add 30.0 ml of 0.05 M sulphuric acid to the flask. Transfer the contents of the flask into a 400 ml beaker; rinse the flask with two quantities, each of 50 ml, of a 200 g/l solution of anhydrous sodium sulphate R and three quantities, each of 20 ml, of water R and add all the rinsings to the beaker containing the initial solution. Titrate the excess sulphuric acid with 0.1 M sodium hydroxide, determining the end-point potentiometrically (2.2.20). Carry out a blank titration.

1 ml of 0.05Msulphuric acid is equivalent to 8.609 mg of vinyl acetate.

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