Protein nitrogen combustion method collaborative study I. Comparison with smalley total Kjeldahl nitrogen and combustion results

During 1993–1994, a collaborative study of the determination of the nitrogen content of oilseed meals by the nitrogen combustion method was conducted among 24 laboratories in seven countries for the analysis of cottonseed, soybean (two samples), peanut, canola and safflower (two samples). These meals were also analyzed by the CuSO4/TiO2 Kjeldahl method (Official Methods and Recommended Practices of the American Oil Chemists' Society, 4th edn., 1989, Method Ba 4d‐90) in the 1993–1994 Smalley Check Sample Program Oilseed Meal Series [Brown, J.,INFORM 5:640 (1994)]. Some participants used commercial nitrogen combustion instruments. In the Smalley Program, CuSO4/TiO2 Kjeldahl analysis gave nitrogen values that ranged from 0.05 to 0.13% lower than values obtained by the combustion method in the collaborative study. Nitrogen values obtained by the combustion method on an optional basis in the Smalley Program were generally lower by 0.01 to 0.03% than nitrogen values obtained by the combustion method in the collaborative study reported here.