KYELDALYA METHOD (J. G. Page of Kjeldahl, the Danish chemist, 1849 — 1900) — a method of quantitative definition of nitrogen in organic compounds and various materials of an animal and plant origin; it is applied in biochemistry and medicine to determination of amount of protein and other connections containing nitrogen in fabrics and liquids of an organism, and also in foodstuff.
In clinic To. the m finds the greatest application during the definition of residual nitrogen in blood, the quantity to-rogo has great diagnostic and predictive value (see. residual nitrogen ). It is offered in 1883.
The method is based on combustion (mineralization) of organic matter in the concentrated chamois to - those (see. Mineralization ). Nitrogen (see), being a part organich. connections, at the same time quantitatively passes in ammonia (see), forming with a chamois to - that ammonium sulfate. At addition of excess of alkali ammonium sulfate decays, and the formed ammonia is driven away in a vessel with precisely measured quantity titrated to - you. Not contacted ammonia to - that titrate (back titration) by alkali in the presence of the indicator: methyl red, bromphenol blue or the indicator of Tashiro representing mix of methyl red and methylene blue. On the basis of results of titration define amount of organic nitrogen. In some micromodifications To. m do not make an otgonka of ammonia at all. Nitrogen of nitrates, nitrites, nitrozo-, nitro - and azo compounds and cyanides at a mineralization with a chamois to - that does not pass into ammonia quantitatively.
Depending on sensitivity distinguish macro - semi-micro and micromodifications To. m. When the studied sample contains not less than 14 mg of nitrogen (apprx. 0,5 g of fabric, 1 — 2 ml of a blood plasma, 5 ml of urine), use macromodification To. m. At use of a semi-micromethod the content of nitrogen in test makes 1,4 — 14 mg. Definition of nitrogen in quantity, smaller 0,14 mg, carry out by Conway's method (see. Conway method ). At Kyeldal's micromethod instead of titration often use colorimetric definition of ammonia with Nessler's reagent (see. Nesslera reactant ), what allows to define shares of mkg of nitrogen in test.
For definition of nitrogen on To. m are required round-bottomed a pear-shaped form — a flask with a capacity up to 100 ml of Kyeldal or a test tube from hard glass, the distillation plant and the receiver. The distillation plant consists of a flask for water, Kyeldal's nozzle protecting distillate from splashes of alkali, and the direct refrigerator (fig). It is desirable that the device for distillation of ammonia was on shlifa.
Serial definitions of nitrogen on To. it is convenient to m to carry out by means of special installations with gas or electric heating in which it is possible to place several flasks of Kyeldal at once.
The hinge plate of the studied material taken on analytical scales (or 2 ml of a protein-free filtrate that corresponds to 0,4 ml of initial blood), is accurately transferred to Kyeldal's flask, pour in 10 ml the concentrated chemically pure chamois to - you, trying as it is possible to moisten better with it a hinge plate at the bottom of a flask. For definition of nitrogen, in a hinge plate of fatty tissue it is necessary to take 15 — 20 ml to - you. Then bring the catalyst in a flask (copper sulfate — 1 g or copper sulfate and potassium sulfate — on 0,5 g). The catalyst increases temperature of boiling to - you. Having allowed a flask to stand not less than 30 min. (it is even better to leave for the night), it is put obliquely in a kolbonagrevatel in an exhaust case and heated on weak fire on an asbestos grid or a sandy bath, avoiding foaming. For sedimentation of foam add a little pure paraffin or octyl alcohol. Then the flask is closed a drop catcher and brought to - that in it to boiling. For acceleration of burning the flask is removed from fire" and add to it several drops pergidrolya. Burning is stopped when liquid from dark brown becomes transparent and colourless. For a mineralization of difficult burning down materials take mix a chamois to - you with phosphoric anhydride and add several drops of metal mercury. Sometimes instead of metal mercury use its salts.
The flask is connected to the device for an otgonka of ammonia which is previously steamed by 5 — 10 min. for removal of traces of ammonia. In the receiver pour 25 — 40 ml 0,1 N a chamois to - you and 2 drops of the indicator. The end of the allonge connecting the refrigerator to the receiver is immersed in to - that. After installation of the receiver in Kyeldal's flask through a funnel flow 50 ml of 33% of solution of caustic soda and begin distillation by means of a superheated steam which, passing through liquid in a flask, carries away with itself(himself) ammonia. The end of distillation can be established on neutral reaction of a drop of distillate from the refrigerator on litmus. Contents of a receiving flask are titrated by 0,1 N solution of caustic soda. Often instead of sulfuric to - you at an otgonka of ammonia use boric to - that. In this case in a flask receiver pour 25 — 30 ml of 2% of solution boric to - you and several drops of the indicator. After an otgonka of ammonia contents of a receiving flask are titrated by 0,1 N a chamois to - that.
At micromodification To. m, except a degrowth of a sample, at titration of the driven-away ammonia for increase in accuracy are used not 0,1 N, but 0,01 N. Sulfuric or salt to - you.
To. the m and its many modifications, napr, use Hau's method offered in 1921 for quantitative definition of protein on nitrogen, so-called azotometrichesky methods of definition of proteins which cornerstone the assumption is that proteins contain on average 16% of nitrogen. Therefore in test with the help To. m determine the content of nitrogen and multiply the received size on 6,25 (100/16). For determination of content of nitrogen in proteins they are besieged from solution trichloroacetic to - that, the deposit is collected on the filter and burned in Kyeldal's flask. In comparison with other methods definition of protein on nitrogen yields more constant and reliable results and often serves as control for check of reliability of other methods.
Bibliography: Biochemical methods of a research in clinic, under the editorship of A. A. Pokrovsky, M., 1969; Colorimetric (photometric) methods of definition of nonmetals, the lane with English, under the editorship of A. I. Busev, page 70, M., 1963; To j e 1 d a h 1 J. Neue Methode zur Bestimmung des Stickstoffs in organischen Korpern, Z. analyt. Chem., Bd 22, S. 366, 1883.
H. H. Zolotov.