SOME LIMITATIONS OF THE KJELDAHL METHOD » 

 By Harvey C. Brill and Francisco Agcaoili 



(From the Laboratory of Organic Chemistry, Bureau of Science, 

 Manila) 



It is an interesting fact that the various chemistry textbooks 

 dealing with analytical methods 2 in describing the Kjeldahl 

 method for the determination of the nitrogen of nitrogenous 

 organic compounds cite only hyrazine, nitro, and similar nitrogen 

 and nitro-oxygen groups as the exceptions, which require special 

 treatment before their total nitrogen can be obtained by this 

 process. 



Recent investigations have shown that compounds other than 

 those enumerated in the above references are resistant to decom- 

 position when subjected to treatment according to the Kjeldahl 

 method or some of its modifications. Pyridine sulphonic acids 

 are prepared by heating pyridine with sulphuric acid. 3 The yield 

 is increased. by the addition of certain metallic sulphates. This 

 increase results from the raising of the temperature of the 

 sulphuric acid solution due to the presence of the sulphate and 

 possibly from the catalytic action of the latter. But more of 

 the sulphonic acid derivative is synthesized in the presence of 

 the sulphate at the higher temperature than in its absence. 



1 Received for publication March, 1917. 



J In Bull. U. S. Dept. Agr. (1912), 107, 5, is the following in regard to 

 applicability of the Kjeldahl and the Gunning methods: "Not applicable 

 in the presence of nitrates." Sudborough, J. J., and James, T. C, in 

 Practical Organic Chemistry, Van Nostrand Company, New York (1908), 

 61, write: "It should be remembered the following groups of compounds 

 do not yield quantitative results unless subjected to a preliminary treat- 

 ment: Nitro, nitroso azo, hydrazo, diazonium compounds and probably 

 cyanogen derivatives and platinichlorides of bases." Leach, A. E., Food 

 Inspection and Analysis, John Wiley & Sons, New York (1914), 69, in 

 discussing the use of the Kjeldahl and the Gunning methods, warns the 

 analyst that: "Neither method in its simplest form is applicable in the 

 presence of nitrates; if these are present, a modification must be used. 

 The Gunning Arnold method is employed for the determination of the 

 nitrogen in pepper, as the piperin is not completely decomposed by the usual 

 processes." 



'Wiedell and Wurman, Monatsh. f. Chem. (1895), 16, 749. Meyer and 

 Ritter, ibid. (1914), 35, 765. 



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