Brown, D. B.

Horton, P. G.

English

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Journal of the Arkansas Academy of ScienceVolume 1 Article 191941Selenium as a Catalyst in the Determination ofKitrogen in Cotton Seed Meal by the KjeldahlMethodD. B. BrownHenderson State UniversityP. G. HortonHenderson State UniversityFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Food Chemistry CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationBrown, D. B. and Horton, P. G. (1941) "Selenium as a Catalyst in the Determination of Kitrogen in Cotton Seed Meal by the KjeldahlMethod," Journal of the Arkansas Academy of Science: Vol. 1 , Article 19.Available at: http://scholarworks.uark.edu/jaas/vol1/iss1/1965SELENIUM AS A CATALYST IN THE DETERMINATION OF NITROGENIN COTTON SEED MEAL BY THE KJELDAHL METHODD. B. Brown Jr.* with P. G. Horton,Henderson State Teachers College, ArkadelphiaThe method almost universally employed Tor the determinationof nitrogen in agricultural and food products is the well knownone devised by Kjeldahl (1) in 1883. Briefly, it consists inboiling the sample in concentrated sulfuric acid which oxidizesthe carbonaceous matter and converts the nitrogen into ammonia.The ammonia at once reacts with the excess acid forming ammoniumsulfate. The acid solution is then diluted, an excess of causticsoda added, and the mixture distilled. The ammonia set free isreceived in a measured volume of standard acid, the excess ofwhich is titrated with standard alkali.Numerous modifications of the original method have beenproposed and used, most of them designed to shorten, by means ofsome catalyst, the period of digestion with the sulfuric acid.Quite a number of substances seem to have the desired catalyticeffect, compounds of copper and mercury being most effective.In 1931, Lauro (2) showed that a small amount of selenium,or certain selenium compounds, if used as catalyst, wouldshorten the time of digestion about one half. To date, sinceLauro 's work, Chemical Abstracts lists over forty papers havingto do with selenium as a catalyst in the determination ofnitrogen by the Kjeldahl method. While his work has been tested,verified, and accepted by a large number of investigators, afew, mostly in the field of cereal chemistry, complain of lowresults with selenium, and ithas not replaced the older catalystsin the official methods. For example, the National CottonseedProducts Association still use mercury or mercuric oxide as thecatalyst in their procedure (3) which is essentially as follows."Digest 1.7034 grams of sample with approximately 0.5 grammetallic mercury or 0.7 gram mercuric oxide, 10 grams of sodiumor potassium sulfate, and 25 cc. of sulfuric acid (Sp. G. 1.84).Place the flask in an inclined position and heat below theboiling point of the acid for from five to fifteen minutes, oruntil frothing has ceased. Increase the temperature and continuedigestion until the liquid has become colorless or until completedigestion has been obtained." (It is common practice to digest70 minutes.)The above procedure not only requires over an hour fordigestion but requires the addition of sodium sulfide toprecipitate the mercury prior to the distillation of the sample.The present work was undertaken to obtain information on therole of selenium as a catalyst in the determination of nitrogenspecifically, in cotton seed meal, for obviously, if seleniumcould be used as a catalyst Instead of mercury, not only wouldthe more or less troublesome use of sodium sulfide be avoided,but a great saving in time of digestion would be effected, andtime is an important item in the commercial testing laboratoriesduring the height of the cotton ginning season.In this investigation, nitrogen was determined in threedifferent samples of cotton seed meal, first by the officialmethod with mercury as catalyst, then by exactly the sameprocedure but substituting selenium for mercury, and omitting*Present address, Solvay Process Company, Hopewell, Virginia.65Journal of the Arkansas Academy of Science, Vol. 1 [1941], Art. 19Published by Arkansas Academy of Science, 194166the sodium sulfide treatment. The amount of selenium and thetime of digestion was purposely varied somewhat. The followingresults were obtained.Amount selenium Time of Nitrogen Nitrogenas catalyst Digestion Se catalyst Off. Method0.75 g. 35 min. 6.480.75 g. 35 min. 6.500.75 g. 35 min. 6.480.75 g. 45 min. 6.48 Avera(Te0.75 g. 45 min. 6.52 av ge 6>560.75 g. 45 min. 6.48 L''4y1.00 g. 45 min. 6.481.00 g. 45 min. 6.481.00 g. 45 min. 6.480.50 g. 35 min. 8.100.50 g. 35 min. 8.180.50 g. 35 min. 8.08 8.10 8.230.50 g. 35 min. 8.080.50 g. 35 min. 8.070.50 g. 35 min. 7.850.50 g. 35 min. 7.860.50 g. 35 min. 7.86 7 Rfi 7 ftR0.50 g. 35 min. 7.89'86 *880.20 g. 35 min. 7.860.20 g. 35 min. 7.83These results seem to warrant the conclusion that seleniumas a catalyst in the determination of nitrogen in cotton seedmeal by the Kjeldahl method, with a shorter digestion period,gives values in fairly close agreement with those obtained bythe official method but definitely lower. This supports theclaim of others that selenium is an effective catalyst but insome cases gives low results.Literature Cited(1) Kjeldahl, "A New Method of Determining Nitrogen In OrganicMaterials" Z. anal. Chem., 22, 366.(2) Lauro. 1931. "Use of Selenium as a Catalyst in Determina-tion of Nitrogen by the Kjeldahl Method"Ind. Eng. Chem., Anal. Ed., Z, 401-2.(3) U. S. Dept. Agriculture. 1939. "Methods of Chemical Analysisand Grade Calculations for Cottonseed", p. 4.66Journal of the Arkansas Academy of Science, Vol. 1 [1941], Art. 19http://scholarworks.uark.edu/jaas/vol1/iss1/19

Selenium as a Catalyst in the Determination of Kitrogen in Cotton Seed Meal by the Kjeldahl Method

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Selenium as a Catalyst in the Determination of Kitrogen in Cotton Seed Meal by the Kjeldahl Method

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