Dissolve about 0.1 g in 10 ml of 0.1 N sodium hydroxide, and add a few drops of cupric sulfate TS
. Warm in a water bath: a purple color develops.
To a test tube containing 25 mg of Zein add 1 mL of nitric acid. Agitate vigorously: the solution becomes light yellow. Further addition of about 10 mL of 6 N ammonium hydroxide produces an orange color.
It is insoluble in water, but 1 g of it in 10 mL of a mixture of isopropyl alcohol and water (85:15), at a temperature of about 37
, yields a clear to cloudy solution.
Proceed as directed under Nitrogen Determination, Method I 461
: the nitrogen content is not less than 13.1% and not more than 17.0%, on the dried basis.