Analytical Method: Phosphorus (Total) in Dairy Products

Photometric determination using the Phosphorus molybdenum blue method subsequent to acid mineralisation

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. 114543 Spectroquant^® Phosphate Cell Test
Cat.No. 114729 Spectroquant^® Phosphate Cell Test
Cat.No. 114848 Spectroquant^® Phosphate 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. 109535 MColorpHastTM Universal Indicator strips pH 0 - 14
Cat.No. 116754 Water for analysis

Sample preparation:
Break up exactly 2 g of the original sample into small pieces and subsequently mix with 10 ml of sulfuric acid for analysis 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 phosphorus, dilute the solution again, pipette 2 ml into a 100-ml volumetric flask and make up to the mark with water for analysis.

Analysis:
Determine with the above mentioned test kits.

Calculation:
Phosphorus (total) content in mg/kg P = analysis result in mg/l P x 5

Literature reference:
Collection of official analysis procedures according to § 35, section 03.00-17 of the German Food Law.