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Total Protein Nitrogen: Evaluation and Comparison of Four Different Methods

1975; Oxford University Press; Volume: 58; Issue: 4 Linguagem: Inglês

10.1093/jaoac/58.4.811

0004-5756

Larry L Wall, Charles W. Gehrke, Terry E Neuner, Robert D Cathey, Paul R Rexroad,

Soil and Water Nutrient Dynamics

Abstract This laboratory has evaluated 2 automated nitrogen methods, the Kjel-Foss and the Missouri-Technicon with block digestor. A modified Kjeldahl method using a low level (40 mg) of CuS04 as a catalyst was also studied. These 3 methods were compared with the official AOAC Kjeldahl method. The experimental set numbered 22 samples, consisting of amino acids, ammonium salts, meals, grains, forages, and American Association of Feed Control Officials check feed samples. This set was analyzed in duplicate 3 independent times by each method. The accuracy and precision values for the 4 methods were excellent, within a very close range, and were equal or superior to the AOAC method. All 4 methods gave average relative standard deviations of <1 %. The 4 methods were compared for rapidity and timeliness of analysis, applicability, cost per sample, and labor and physical requirements to provide those who are responsible for protein nitrogen analysis with a basis for choosing a nitrogen method that would be most suitable for their needs.