Effect of sample introduction and atmospheric blank on determination of nitrogen (crude protein) by combustion
1997
Sachen, R.W. | Thiex, N.J.
To reduce analysis time, reagent use, and chemical waste, existing Kjeldahl methods for crude protein were converted to combustion methods. When validating the combustion method for various samples, a high bias for the combustion method compared with the Kjeldahl method was apparent for high-fiber samples. The bias was sample dependent, varying from 0.15 to 1.38% crude protein for hay and corn silage samples. The bias was repeatable among 3 laboratories using identical instruments. Studies showed the bias was related to uncorrected atmospheric blanks. Various means to correct for the blank were studied, including pelleting of sample under high pressures to remove atmospheric nitrogen. Pelleting samples at a pressure of >1000 lbs provides combustion crude protein values consistent with Kjeldahl values.
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