Protein Determination Steps with Kjeldahl Nitrogen Analyzer

Step 1: Sample Digestion

1. Sample weighing --- use a ten-thousandth balance

2. Put the weighed sample into the digestion tube, add concentrated sulfuric acid (10-15ml), add the catalyst 3g potassium sulfate, 0.2g copper sulfate (catalyst tablet ratio)

3. Put the digestion tube on the digestion furnace for digestion, usually until the color of the sample is clear

Step 2: Distillation with Nitrogen Analyzer

1. Put the digested and cooled digestion tube into the nitrogen analyzer, and add 40ml of alkali liquor (3-4 times the amount of concentrated sulfuric acid) into the digestion tube

2. Properly add dilution water according to the volume of the digestive tube after adding alkali liquor

3. Put a triangular beaker at the position of the effluent, and add about 25ml of boric acid absorption solution into the triangular beaker

4. Set the distillation time, generally 300-400s

Step 3: Titration

1. Add a color indicator to the Erlenmeyer flask receiving the effluent. Mix indicator and boric acid solution at a ratio of 1:100, for example: add 10ml indicator to 1000ml boric acid solution.

2. Titrate with standard titration solution, and judge the titration end point by color

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