Analytical Method: Urea in water and wastewater

Reagents and accessories:
100573 ortho-Phosphoric acid 85 % for analysis
100731 Sulfuric acid 95 - 97 % for analysis
103943 Iron(III) chloride hexahydrate for analysis
102918 Diacetyl monoxime for analysis
108156 Thiosemicarbazide for analysis
116754 Water for analysis
114724 Empty cells 16 mm with screw caps
Thermoreactor
 
Reagent 1:
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 2:
Mix  27 g of diacetyl monoxime and 0.77 g of thiosemicarbazide and homogenize.
 
Reaction:
Urea forms with oximes in acidic and oxidizing mediums colored products. These products are suitable for a photometric determination. Diacetyl monoxime and diacetyl dioxime are usual reagents for this purpose.
 
Measurement range:
0.5 - 5.0 mg/l urea in a round cell at 525 nm.
 
Analysis:
Mix 5.0 ml of the sample solution with 2.0 ml of reagent 1 and 50 mg of reagent 2 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.
 

 

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

 

Method number ----
Method-designation urea
Wavelength 525 nm
Citation urea
Units mg/l
Resolution 0.01
Zero point (E0) 0.000
Slope (E/C) 0.465
Meas. range begin 0.50
Meas. range end 5.00
Reference cell 16 mm round


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

 

Measured absorbance
of samples in A
Result in mg/l
[A sample * 1 / 0.465]
1.000 2.15



Parameter list for programming the photometer SQ 118

 

01 Method urea
02 Cat.No. -------
03 Measuring range 0.50 - 5.00
04 Units mg/l
05 Reaction time 6 10 min
06 Cell 16 mm round
07 Wavelength 525 nm
08 Calibration Factor
09 Evaluation Linear
10 Factor 2.15

 

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

 

Measured absorbance
of samples in A
Result in mg/l
[A sample * 2.15]
1.000 2.15

 

 

Materials

     
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