Analytical Method: Nitrogen (total) in dairy products

Instruments and Reagents:

Cat.No. 173016  Spectroquant® VIS Spectrophotometer Prove 100 or

Cat.No. 173017  Spectroquant® UV/VIS Spectrophotometer Prove 300 or

Cat.No. 173018  Spectroquant® UV/VIS Spectrophotometer Prove 600 or

Cat.No. 109748  Spectroquant® Photometer NOVA 30 or

Cat.No. 109751  Spectroquant® Photometer NOVA 60 or

Cat.No. 173632  Spectroquant® Colorimeter Move 100

Cat.No. 114946  Rectangular cells 10 mm and/or

Cat.No. 114947  Rectangular cells 20 mm and/or

Cat.No. 114944  Rectangular cells 50 mm
Cat.No. 114537  Spectroquant® Nitrogen Cell Test
Cat.No. 100613  Spectroquant® Nitrogen Cell Test*
Cat.No. 114763  Spectroquant® Nitrogen Cell Test*
Cat.No. 100731  Sulfuric acid 95 - 97 % for analysis
Cat.No. 107209  Hydrogen peroxide 30 % (Perhydrol®) for analysis
Cat.No. 105590  Sodium hydroxide solution 32 %
Cat.No. 116754  Water for analysis
       
*not compatible with Move 100
   
Sample preparation:
Break up exactly 2 g of the original sample into small pieces and subsequently mix with 10 ml of sulfuric acid in a 400-ml glass beaker. Weakly heat the mixture on a hob in the fume cupboard. Carefully add portion by portion 10 ml of Perhydrol® to the mixture. After the reaction has finished (development of gas, strong foaming), heat until SO3 begins to develop. If the mixture turns brown or black in color, cool, add 10 ml of Perhydrol®, and reheat. Repeat this procedure as many times as are necessary to produce a clear, colorless solution. As a rule 30 to
40 ml of Perhydrol® is required for this procedure.
Completely boil off the superfluous Perhydrol®, cool the residue, dilute with a little water for analysis, and adjust the pH on the pH-meter to a value of 6 - 7 with sodium hydroxide solution 32%. Transfer the solution to a 200-ml volumetric flask and make up to the mark with water for analysis.
For determination of total nitrogen, dilute the solution again, pipette 5 ml into a 100-ml volumetric flask and make up to the mark with water for analysis.
 
Analysis:
Determine with the above mentioned test kit.
 
Calculation:
Nitrogen (total) content in g/kg N = analysis result in mg/l N x 2
 
Literature reference:
Collection of official analysis procedures according to § 35, section 03.00-17 of the German Food Law.

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