The nitrogen content of starch and its derivatives is usually determined by the Kjeldahl method.
The steps for determining the nitrogen content of starch and its derivatives by Kjeldahl method are as follows:
Sample preparation: Weigh 1 gram of the starch or starch derivative sample and put it into the digestive tube.
Digestion: add 5 ml of concentrated sulfuric acid, heat to 180°C for about 1 hour to digest the sample completely, and generate NH4+.
Distillation: Transfer the contents of the digestion tube to a distillation flask, add 50 ml of distilled water, add NaOH and saturated potassium hydroxide, and cool the distillation flask with cooling water. Connect the distillation bottle to the distillation device, heat to boiling, distill ammonia gas, and collect the distillate.
Titration: Add the collected distillate into potassium hydroxide solution, titrate with hydrochloric acid solution until the color of the acidity indicator changes, and record the number of titrations.
Calculation: Calculate the nitrogen content in the sample according to the titration times, and finally convert it to the nitrogen content of starch or starch derivatives.
The formula for calculating the nitrogen content of starch or starch derivatives is:
Nitrogen content (%) = titration value × N × 1.4 / sample mass
Among them, N is the molar concentration of hydrochloric acid, and 1.4 is the coefficient of NH4+ being converted into nitrogen.
Beichao reminds you: During the operation, the experimental conditions should be strictly controlled, and multiple measurements should be made to improve the measurement accuracy.
