How do you solve the problems encountered during protein determination?
Protein determination problems
I am a beginner. When I measure crude protein in the lab, the digested material does not change color when alkali is added, and the solution is clear blue. It has been like this several times. I do not know where the problem is. Could everyone help analyze what the reason is?
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I do not understand what you mean. Are you saying the liquid after digestion and distillation does not change color when it meets alkali?
510228206 added the following content on 2009-9-14 09:41
We use boric acid for absorption. How can alkali be used? I am a bit confused.
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What are the results like? When we do it, it is not always colored either. Sometimes it is blue, sometimes brown. It will not all be the same depending on different raw materials, finished products, and different formula compositions. If anyone knows the specific principle and reaction, it would be greatly appreciated if you could give a chemical reaction equation! Looking forward to it......!
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Yes, it is the liquid after digestion and distillation that does not change color when it meets alkali.
[ts]jiangwenbo119 added the following content on 2009-9-14 10:49[/ts]
3# 372637000
The result is incorrect. Basically no ammonia gas is produced.
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Use concentrated sulfuric acid (H2SO4) for digestion and decomposition (that is, decompose all organic matter with concentrated sulfuric acid into a transparent solution), so that nitrogen-containing compounds in various forms (proteins, amino acids, etc.) are all converted into one form, ammonium ions (NH4+). In this way, the classic acid-base titration method can be used to determine the nitrogen content, and then multiply by a certain conversion factor to obtain the protein content. The conversion factors differ slightly among different substances. Generally, dairy products are 6.38, rice 5.95, peanut 5.46, flour 5.70, corn and sorghum 6.24, soybean and its products 5.71, meat and meat products 6.25, barley, millet, oats, and rye 5.83, sesame and sunflower 5.30 (this is related to the protein structure in them).
Converted to protein content: that is, w(protein)=w(N)*factor.
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I do not understand what the problem is. Please explain more clearly. Protein determination is very simple. What equipment are you using, a nitrogen analyzer or Kjeldahl distillation?
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The national standard uses boric acid absorption! Is there a problem with the method you are using? Follow the national standard and there will be no problem!!!!!!!!!!
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The digestion liquid after digestion has been left for too long, and the digestion liquid is too cold. Pass steam through it for a while and then add alkali, and it will be fine.
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When adding alkali during protein distillation, sometimes it does not change color, sometimes it is brown-black flocculent, and sometimes it is just blue. Whether there is a problem depends on your results. If the result is low, it may be that the amount of alkali added is not enough.
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I agree with the opinion above. A low result is not only due to insufficient alkali, but may also be due to an error in the concentration of the standard solution. Have you verified it with ammonium sulfate?
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We have also encountered this situation. It should be a problem with the sample itself. As long as the results obtained do not differ much, there is not much of a problem.
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Learn, learn! Learn, learn! Learn, learn! Learn, learn! Learn, learn! Learn, learn!
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I do not understand what you mean. Are you saying the liquid after digestion and distillation does not change color when it meets alkali?
510228206 added the following content on 2009-9-14 09:41
We use boric acid for absorption. How can alkali be used? I am a bit confused.
--------------------------------------
What are the results like? When we do it, it is not always colored either. Sometimes it is blue, sometimes brown. It will not all be the same depending on different raw materials, finished products, and different formula compositions. If anyone knows the specific principle and reaction, it would be greatly appreciated if you could give a chemical reaction equation! Looking forward to it......!
--------------------------------------
Yes, it is the liquid after digestion and distillation that does not change color when it meets alkali.
[ts]jiangwenbo119 added the following content on 2009-9-14 10:49[/ts]
3# 372637000
The result is incorrect. Basically no ammonia gas is produced.
--------------------------------------
Use concentrated sulfuric acid (H2SO4) for digestion and decomposition (that is, decompose all organic matter with concentrated sulfuric acid into a transparent solution), so that nitrogen-containing compounds in various forms (proteins, amino acids, etc.) are all converted into one form, ammonium ions (NH4+). In this way, the classic acid-base titration method can be used to determine the nitrogen content, and then multiply by a certain conversion factor to obtain the protein content. The conversion factors differ slightly among different substances. Generally, dairy products are 6.38, rice 5.95, peanut 5.46, flour 5.70, corn and sorghum 6.24, soybean and its products 5.71, meat and meat products 6.25, barley, millet, oats, and rye 5.83, sesame and sunflower 5.30 (this is related to the protein structure in them).
Converted to protein content: that is, w(protein)=w(N)*factor.
--------------------------------------
I do not understand what the problem is. Please explain more clearly. Protein determination is very simple. What equipment are you using, a nitrogen analyzer or Kjeldahl distillation?
--------------------------------------
The national standard uses boric acid absorption! Is there a problem with the method you are using? Follow the national standard and there will be no problem!!!!!!!!!!
--------------------------------------
The digestion liquid after digestion has been left for too long, and the digestion liquid is too cold. Pass steam through it for a while and then add alkali, and it will be fine.
--------------------------------------
When adding alkali during protein distillation, sometimes it does not change color, sometimes it is brown-black flocculent, and sometimes it is just blue. Whether there is a problem depends on your results. If the result is low, it may be that the amount of alkali added is not enough.
--------------------------------------
I agree with the opinion above. A low result is not only due to insufficient alkali, but may also be due to an error in the concentration of the standard solution. Have you verified it with ammonium sulfate?
--------------------------------------
We have also encountered this situation. It should be a problem with the sample itself. As long as the results obtained do not differ much, there is not much of a problem.
--------------------------------------
Learn, learn! Learn, learn! Learn, learn! Learn, learn! Learn, learn! Learn, learn!