Añadiendo a la muestra 10 ml de ácido sulfúrico 96% y dos tabletas del Catalizador Kjeldahl (Cu) (10,26% en CuSO4.5H2O) y poniendo el digestor a 400 ºC debería de digerirse toda la muestra.

Saludos

I already add 15 ml H2SO4 96% with 1 tablet at 220 ºC 1 hour then 410 ºC another hour  

For Ca and P samples, I ash at 520  ºC for 4 hours then I add 20 ml of Hcl (5 m) for 10 hours and still the samples not clear. you can see the tubes sample for crude protein and the crucible samples for Ca and P analysis

now the protein samples after 3 hourse digestion at 410 ºC and for Ca samples after 5 hours digestion and I complete 10 hours with same color.

Es muy raro lo que te pasa. Debes comprobar que el digestor realmente alcanza los 400 ºC.

I think it could be a missing obtain in one of the agents (solvents or catalyst, etc.)which used in the digestion process of food samples. because that procedure is routine to get the result. Good luck.

Incomplete digestion, evident by dark particles in digested samples may cause

low results. When this occurs, the original sample must be diluted and

redigested.

 dear  i  think it  may be  a missing obtain in one of the agents (solvents or catalyst, .)which used in the digestion process of food samples. because that procedure is routine to get the result

U have to put cupric selenic and add more concentrated H2SO4 and observe your sample until it's clear digested

 I dont have any missing in one of my agents and my sample weight 0.1 g. Also, I used tablet high selenium.

My suggestion : only reduce the weight of the sample.

you can use another catalyst formula like K2SO4 : CuSO4 2:1 and 10-20 ml H2SO4 98% and raise the final Temp. to 450C

ok, I will decrease the weight but may I know can determine the crude protein by NC Soil Analyzer. the mechine for determine nitrogen without digestion. Normally, it use for determine the nitrogin in the soil. Can I determine the nitrogin in tissue samples by this mechine? 

you can check your agents (H2SO4), check the temperture ?? good luck!

I think that the method you use is not adequate, you do not need to do digestion, simply dries in forced air stove and samples after it follows the KJELDAHL METHOD

I suggest you to follow the standard procedure for digestion of sample for crude protein determination i.e., kjeldahl method for this  please add catalyst mixture containing cuso4. SeO2 and K2SO4; and conc. H2SO4 with sample and digest.

Hello Mohammed:

Several things can be going on here.

(a) Your sample type: You said you are digesting waste chicken meat and rice ; Does the meat have bones, skin, collagen and keratin? Such proteins can be tough because they contain amino acid prolein, hydroxyprolein.  You can facilitate digestion by mincing the meat waste first or grinding it to a a soft mushy substance, Weigh out a little quantity of the minced product,and use it in your digestion.

(b) The acid used in digestion and the Protein determination  method:

If you are using the Kjeldahl method, use a strong concentrated sulfuric acid, plus catalysts  and follow the protocol outlined in the Kjeldahl procedure. Careful , and use personal protective equipment(Eye Goggles, gloves, gowns etc) or else the strong acid can burn and damage eyes and skin.Some people also use the Lowry method. I found digestion using Kjeldahl method convenient when I was working on legumes and cereal grains.

(c) The ratio of acid  to sample size. Increase the ratio of acid to sample. Weigh out a small minced sample and use enough acid to cover it up and start digesting(heat is involved). Use a small sample,later after determining the nitrogen per gram of sample, you multiply your nitrogen value by 6.25 to give you amount of protein per gram of sample. You can then scale it up in the calculation by determining amount of protein per 100 gram of sample  as well as nitrogen and protein  in your original sample.

Determination of Nitrogen in the soil uses a different procedure. Consult the AOAC handbook of analysis for soil samples.

Good luck!

Dr Stella G Uzogara

Please see my responses on these questions 6 days ago on acid  digestion of food waste samples.

In addition if you have the right equipment, reduce particle size of sample , add water mix , freeze, and  freeze-dry. Grind the freeze dried powdered sample and use a few grams of the powder for  your Kjeldahl analysis. Then determine your nitrogen and protein content of samples. Thanks.

Dr Stella Uzogara

Thank you for all who help me by sharing his/her knowledge and expert. I appreciate assistance of Dr Stella Uzogara and I will follow your instructions.