ChemSpec 150


RAPID AND ACCURATE METHOD FOR THE DETERMINATION OF UREA IN COW's MILK


Chemspec 150

 

 

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ChemSpec Analytical Specifications

Analytical range

Performance

*specifications for typical raw milk samples.

 

Principle :

This method is based on a modified Berthelot reaction. A small amount of milk is automatically sampled and dispensed in a thermostated well and split enzymatically with urease into ammonia and carbon dioxide. After the incubation time, a dye and an activator are added to the mix to form a green complex which intensity is correlated to the ammonia concentration, thus the urea concentration. The green color intensity is measured spectrophotometrically in a trans-reflectance cell and translated into an urea value after instrument calibration.

The addition of a catalyst in the dye speeds up the reaction, intensifying the green color development, thus enhancing the sensitivity of the method.

The use of a highly precise sample dispenser allows to bypass the pre-dilution step. The milk is simply diluted in the chemicals used to generate the reactions. This dilution reduces the opacity of the medium, thus improving the spectrophotometric measurement, and prevents interferences with the other milk components.

The use of the Differential Mode, determination of the natural ammonia due to the bacteria proteolytic activity and the converted ammonia allows to precisely determine the true urea concentration. The Differential Mode is also canceling out any interferences that were not removed with the dilution.

The Bentley ChemSpec is equipped with a solid-well carrousel which allows to overlap several analysis and reach a capacity of 150 samples per hour.

 

    Table 1. Repeatability study : Mean, Standard Deviation and Coefficient of Variation for the MUN determination in 30 samples based on five consecutive determination.

MUN [mg/dl]

SDDr

CVr(%)

8.91

0.205

2.21

10.06

0.147

1.54

10.73

0.108

1.03

11.79

0.150

1.41

12.15

0.132

1.07

13.33

0.160

1.16

13.36

0.190

1.39

14.45

0.156

1.09

14.56

0.180

1.22

16.03

0.172

1.10

16.20

0.144

0.87

17.02

0.187

1.09

18.00

0.167

0.95

18.27

0.306

1.61

18.66

0.175

0.96

18.89

0.232

1.20

18.89

0.272

1.44

19.05

0.152

0.78

19.51

0.202

1.01

20.06

0.211

1.07

20.41

0.112

0.55

21.74

0.179

0.84

21.86

0.293

1.30

22.32

0.211

0.99

23.07

0.420

1.78

23.20

0.321

1.43

24.27

0.342

1.42

24.30

0.383

1.55

25.18

0.161

0.64

25.52

0.214

0.86

Average

0.21

1.19

 

    Table 2. - Precision of different urea determination methods, given as relative values of the repeatability.

Method

n

CVr(%)

Reference

Boehringer-Mannheim

5

0.4

Wolfschon-Pombo and al.(1981)

Autoanalyzer, DAM

46

0.5

De Jong and al.(1992)

ChemSpec

30

1.19

Broutin (1997)

FIA

 

0.5<0.8<1.2

Oltner and al. (1985)

IL919

20

1.4

Oltner & Sjaunja(1982)

CL-10

 

<1.5

Instrument Specification

FIA

10

0.8<2.0<4.0

Andersson and al. (1986)

FIA

 

2.1

Carlsson & Bergstrom(1994)

Foss4000

645

5.0

Anderson and al(1995)

IR B2000

300

6.0

Lyder(1997)