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HomeChemical Analysis for Food and Beverage TestingAnalytical Method: Urea in Milk (Photometry)

Analytical Method: Urea in Milk (Photometry)

Reagents and Accessories

Product No. 100807 Trichloroacetic acid for analysis
Product No. 116754 Water for analysis
Product No. 100573 ortho-Phosphoric acid 85 % for analysis
Product No. 100731 Sulfuric acid 95 - 97 % for analysis
Product No. 103943 Iron(III) chloride hexahydrate for analysis
Product No. 102918 Diacetyl monoxime for analysis
Product No. 108156 Thiosemicarbazide for analysis
Product No. 114724 Empty cells 16 mm with screw caps
Folded filter
Thermoreactor

Reagent 1

Mix 20 g of trichloroacetic acid and 80 mL of water for analysis and dissolve.

Reagent 2

Mix 100 mL of phosphoric acid 85 %, 100 mL of sulfuric acid 95 - 97 %, and 0.45 g of iron(III) chloride hexahydrate and dissolve.

Reagent 3

Mix 27 g of diacetyl monoxime and 0.77 g of thiosemicarbazide and homogenize.

Sample preparation:

Pipette 50 mL of milk into a 100-mL volumetric flask. With swirling add 20 mL of reagent 1, make up to the mark with water for analysis, and mix. Centrifuge this mixture for 15 minutes (4000 rpm). Also filter the supernatant through a folded filter. The result is a slightly turbid solution; dilute this solution 1 + 49 with water for analysis. The total dilution is 1+99.

Analysis

Mix 5.0 mL of the clarified and diluted solution with 2.0 mL of reagent 2 and 50 mg of reagent 3 and heat in the closed blank cell in the thermoreactor to 100 °C for 6 minutes. Subsequently immediately cool the blank cell to room temperature in an ice-water bath and leave to stand for 10 minutes. In the presence of urea the solution turns red. Swirl the sample and measure the absorbance at 525 nm against a blank solution prepared using the respective reagents.

Calculation

Urea content in mg/l = analysis value in mg/l x 100

Parameter list for programming the photometer Spectroquant® NOVA 60, NOVA 400, Pharo 100, and Pharo 300

Calculation when measuring the absorbance value using the above NOVA photometers without programming the method in the memory of the instrument:

Parameter list for programming the photometer SQ 118

Calculation when measuring the absorbance value using the photometer SQ118 without programming the method in the memory of the instrument:

Materials
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