Animal feed science and technolog

Animal Feed Science and Technology 73 (1998) 21±28

A comparison of nitrogen values obtained utilizing the Kjeldahl nitrogen and Dumas combustion methodologies (Leco CNS 2000) on samples typical of an animal nutrition analytical laboratory
R.D. Etheridgea,*, G.M. Pestib, E.H. Fostera
a

Poultry Science Research Laboratory, Livestock-Poultry Building, University of Georgia, Athens, Georgia30602-2772, USA b Department of Poultry Science, Livestock-Poultry Building, University of Georgia, Athens, Georgia 30602-2772, USA Received 24 March 1997; accepted 7 January 1998

Abstract The Dumas combustion procedure using Leco's CNS 2000 analyzer has been shown to give nitrogen values comparable to those obtained with the Kjeldahl procedure for soil and plant products (slightly higher formost samples). These procedures were compared for a range of samples more typical for an animal nutrition laboratory (feed, excreta, carcass, egg yolk, milk and urine). For the 36 samples compared, the Kjeldahl procedure gave N values slightly lower than the Dumas procedure: NKjeldahl ˆ 0X0103 ‡ 0X9855  NCNS . The coefficient of variation for standard AAFCO broiler and cattle feeds (measuredrepeatedly over an 18-month period) were 2.23 (nˆ90) and 2.12 g/100 g (nˆ177), respectively. It was concluded that the Dumas combustion procedure is capable of replacing the Kjeldahl procedure for routine animal nutrition laboratory N analyses. The Dumas procedure has the advantages of using fewer strong reactants, requiring less labor, and uses a more efficient temperature to release the nitrogen fromthe samples than the Kjeldahl procedure. # 1998 Elsevier Science B.V.
Keywords: Nitrogen; Kjeldahl; Dumas; Protein; Combustion

* Corresponding author. Fax: 706/542-1827; e-mail: retherid@uga.cc.uga.edu 0377-8401/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved PII S 0 3 7 7 - 8 4 0 1 ( 9 8 ) 0 0 1 3 6 - 9

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R.D. Etheridge et al. / Animal Feed Science and Technology 73 (1998)21±28

1. Introduction Because of increasing government regulations and the increase in cost for disposal of hazardous materials, the Dumas combustion technique (Dumas, 1826 as cited by Buckee, 1994) for total nitrogen has received much attention in recent years. McGeehan (1988) reconfirmed that the Kjeldahl nitrogen value for materials containing nitrates were lower than values obtained usingcombustion techniques. In general, the combustion process gave slightly higher nitrogen values than wet oxidation techniques when analyzing plant material (Jones, 1992; Buckee, 1994; Simonne et al., 1995). Soil nitrogen values obtained by the Kjeldahl analysis were lower than those obtained with the combustion process although Wang (1993) concluded that the Kjeldahl procedure gave better precisionand accuracy than the combustion technique on finely ground samples. It appears that more research data are needed on soils to determine which procedure is the most accurate. The Dumas combustion method has been adopted as a alternative technique for total nitrogen by the feed industry (Sweeney, 1989) and as the official reference method by the Brewing industry (Buckee, 1994). The next few yearswill probably be a transition period from the Kjeldahl procedure which utilizes many hazardous materials to the environmentally friendly combustion technique. The purpose of the experiments described here were to compare the Kjeldahl and Dumas nitrogen procedures using a variety of samples typical of an animal nutrition analytical laboratory. 2. Materials and methods 2.1. Samples analyzed Onehundred and twenty-six samples from animal nutrition feeding trials with a broad range of nitrogen contents were randomly chosen from samples submitted to our laboratory (8±180 g kgÀ1 N; Table 1). The feed and excreta samples were milled to pass a 1.0 mm screen (Wiley Mill; Arthur H. Thomas, Philadelphia, PA, USA). Excreta samples were dried at 708C overnight in a forced air oven, after which they...