Kjeldahl Vs Soxhlet

[dave]

Hi all,
Hope this message finds you well and your week has started without any of the usual lab mishaps!!!

I would be grateful if someone could tell me if the kjeldahl method can be substituted for soxhlet method. trying to put some methods together for some agricultural testing in relation to crude fibre and crude oil determination in animal feed, the methods i have and some that i have seen use the kjeldahl method, as i have a soxhlet set up i was wondering if this can still do the same job.

Kind Regards

Dave

[HW Mueller]

I have seen the name Kjeldahl only in connection with total nitrogen determination.

[Jumpshooter]

I have used Kjeldahl to determine total nitrogen % in leaf, tissue, root nodules, and beans/fruits--with acid digest. I have used soxhlets to quantify dioxin congeners in pulp/paper matrices--with boiling in toluene and rotary evap and ultimately GCMS. I suppose you could extract your plant biochemicals of interest using the soxhlet or other feasible organic solvent extraction techniques. "Multiple paths to the same answer"--type of thing OK?

[Don_Hilton]

I think the short answer is:

Soxhlet is a method of extraction of materials from matrix.

Kjeldhal is a method of quantification of organic nitrogen.

They are not the same, nor do they do the same job.

[CE Instruments]

Agree with the above and if you have to run Total Nitrogen Kjeldhal in any quantity and/or do not already have a system then don't Get an Elemental analyser that will do Carbon , Hydrogen and Sulphur as well as Nitrogen Oxygen too by pyrolysis
Kjeldhal does not give 100% recovery for most samples, uses strong acids (at boiling point) and in some cases requires toxic catalysts too. I have to admit a bias , we supply Thermo OEA kit see my web link

[dave]

Thanks for the response all, subject alot clearer

[alexdwsn12]

Soxhlet is an physical extractive method for fats while Kjeldahl is a chemical method for % nitrogen in animal feed which is not interchangeable. Kjeldahl was the director of research at the chemical laboratory of the Carlsberg brewery.

[PhotonicGuy]

“Kjeldahl was the director of research at the chemical laboratory of the Carlsberg brewery.â€

[HW Mueller]

They probably wanted an estimate on the value of the barley by estimating protein content?

[Don_Hilton]

From somewhere in the back of my memory, it seems that protein content is important to the formation of the head on the beer.

[lmh]

Kjeldahl gets rid of some difficult letters in Scrabble, but soxhlet has a useful "x".