Kjeldahl nitrogen analyzer principle and operation steps (nitrogen distiller)
Kjeldahl principle:
Proteins are organic compounds containing nitrogen. The food is heated and digested together with sulfuric acid and a catalyst to decompose the protein, and the decomposed ammonia combines with sulfuric acid to form ammonium sulfate. The alkalization distillation then releases the ammonia, absorbs it with boric acid, and then titrates it with a standard solution of sulfuric acid or hydrochloric acid, and multiplies the conversion factor by the acid consumption, which is the protein content.
? Kjeldahl nitrogen analyzer principle and operation steps (nitrogen distiller)
1.
Amine in organic matter is strong and
CuSO4
,concentrated
H2SO4
Nitrification
(NH4)2SO4
The reaction formula is:
2NH2+H2S04+2H
=
(NH4)2S04 (
among them
CuSO4
Catalyst
)
2.
Acting with alkali in Kjeldahl nitrogen, released by distillation
NH3
, collected in
H3BO3
In solution
The reaction formula is
: (NH4)2SO4+2NaOH
=
2NH3+2H2O+Na2SO4 2NH3+4H3BO3
=
(NH4)2B4O7+5H2O
3.
Using known concentrations
H2SO4(
or
HCI)
Standard solution titration, according to
HCI
The amount consumed is calculated as the nitrogen content, and then multiplied by the corresponding conversion factor to obtain the protein content.
The reaction formula is:
(NH4)2B4O7+H2SO4+5H2O
=
(NH4)2SO4+4H3BO3
(NH4)2B4O7+2HCl+5H2O
=
2NH4Cl+4H3BO3
Kjeldahl nitrogen analyzer principle and operation steps (nitrogen distiller)
Kjeldahl nitrogen analyzer steps:
(
one
)
digestion
1
,ready
6
Kjeldahl flasks, numbered.
1
,
2
,
3
Add the appropriate concentration of protein solution to the flask
1.0mL
The sample should be added to the bottom of the flask. Do not stick it on the bottle mouth and bottle neck. Add potassium sulfate in turn
-
Copper sulfate contact agent
0.3g
Concentrated sulfuric acid
2.0mL
,
30%
hydrogen peroxide
1.0mL
.
4
,
5
,
6
The flask was used as a blank control to determine the trace amount of nitrogenous substances that may be contained in the reagent, and the sample was corrected.
4
,
5
,
6
Distilled water in the flask
1.0mL
Instead of the sample solution, the remaining reagents and
1
,
2
,
3
The flask is the same.
2
Place the flasks with the reagents on the digesting rack and connect the pumping device. First, boil it with a slight heat. At this time, the material in the flask becomes carbonized and black, and a large amount of foam is generated. Care must be taken to prevent bubbles from rushing out of the nozzle. After the foam disappears and stops, increase the firepower and keep the liquid in the bottle slightly boiling. After the solution is clarified, continue heating to make the digestive juice slightly boil.
15min
. The flask should be rotated at any time during the digestion process so that the adhesive material on the inner wall can flow into the bottom to ensure complete digestion of the sample. Gas contained during digestion
SO2
It is highly irritating, so the pump should be turned on from the beginning to the end to pump the gas into the tap water. The entire digestion process should be carried out in a fume hood. After the digestion was complete, the flame was turned off and the flask was allowed to cool to room temperature.
(
two
)
Distillation and absorption
Distillation and absorption were carried out in a micro-Kjeldahl instrument. There are many types of Kjeldahl distillation plants, which are generally composed of three parts: steam generation, ammonia distillation and ammonia absorption.
Instrument washing
Before the instrument is installed, all parts must be cleaned by general methods. The rubber hoses and plugs used should be immersed in
10% NaOH
In the solution, cook about
10min
, washed, boiled
10min
, washed several times, then installed and fixed on an iron stand.
Kjeldahl nitrogen analyzer principle and operation steps (nitrogen distiller)
Before the instrument is used, all traces of the pipe must be washed with steam to remove any ammonia that may remain in the pipe. The instrument being used, before each sample, steam wash
5min
Just fine. For instruments that have not been used for a long time, repeat the steam wash, no less than three times, and check if the instrument is normal. Carefully inspect the connections to ensure that there are no air leaks.
First add in the steam generator
2/3
Volumetric distilled water, add a few drops of sulfuric acid to keep it acidic, to avoid the ammonia in the water being distilled out to affect the result, and put a little zeolite
(
Capillary, etc.
)
To the explosion-proof boiling. Add distilled water along the wall of the small glass
20mL
Let the water flow into the reaction chamber through the cannula, but the water in the glass should not be lighted, plug the rod-shaped glass plug, keep the water seal and prevent air leakage. Immediately after the steam occurs, the switch on the waste liquid discharge pipe is closed, so that the steam can only enter the reaction chamber, causing the water in the reaction chamber to boil rapidly. The steam is distilled from the upper port of the reaction chamber through the nitrogen-fixing ball into the condenser to be cooled, in the condensation tube. Place a conical flask on the lower end to receive the condensate. Start from the time when the nitrogen ball is hot, continuous cooking
5min
Then remove the gas lamp. After the flushing is completed, the connecting rubber tube between the steam generator and the collector is clamped. Since the gas cooling pressure is lowered, the waste liquid in the reaction chamber is automatically drawn into the reaction chamber casing, and the waste liquid discharge port clamp is opened to discharge the waste liquid. So clean
2
~
3
Second, then exchange a boric acid under the condenser
-
The conical flask of the indicator mixture makes the lower end of the condenser tube completely immersed in the solution, distillation
1
~
2min
Observe whether the solution in the Erlenmeyer flask is discolored. If it does not change color, it means that the inside of the distillation unit has been cleaned. Remove the conical flask and distill it
1
~
2min
Rinse the condenser bottom with distilled water and turn off the gas lamp. The instrument can be used for sample measurement.
Distillation absorption of inorganic nitrogen standard samples
Due to the cumbersome operation of nitrogen determination, in order to be familiar with the operation techniques of distillation and titration, beginners should first practice repeatedly with inorganic nitrogen standard samples, and then measure organic nitrogen unknown samples.
Kjeldahl nitrogen analyzer principle and operation steps (nitrogen distiller)
Stretch Bar Display,Stretched Bar Lcd Display,Digital Advertising Screen,Stretch Bar Lcd Display
APIO ELECTRONIC CO.,LTD , https://www.displayapio.com