CONWAY METHOD

From Big Medical Encyclopedia

CONWAY METHOD (E. J. Conway) — quantitative definition of ammonia with use of the principle of an isothermal otgonka. It is applied to definition of ammonia in solutions, and also in blood, urine and at the enzymatic reactions which are followed by release of ammonia. It is offered in 1933.

The emitted ammonia of test communicates a chamois to - that; from solution of the formed ammonium sulfate ammonia is forced out strong alkali.

Conway's Cup: 1 — an external part (for the studied test and alkali liquor); 2 — the internal cylinder (for sulphuric acid).

The released ammonia is absorbed by the titrated solution to - you. Decomposition of ammonium sulfate and absorption of ammonia carry out in Conway's (fig.) cups.

Conway's cup in a form reminds a glass laboratory crystallizer to dia. 7 — 8 cm, in the central part to-rogo the additional (internal) cylinder to dia is sealed. 3 cm. Edges of a cup grease with vacuum lubricant. In the internal cylinder pour titrated sulfuric to - that, in an external part of a cup — the studied test, add alkali here; the cup is quickly closed glass, rocking merge alkali and the studied test and left to stand before the end of diffusion of ammonia from podshchelochenny test in sulfuric to - that, poured to the interior cups. After the end of absorption of the emitted ammonia to - by that (usually in 18 — 24 hours) its quantity is determined colorimetric.

In practice of medical - biol, laboratories various modifications of a method are used. Instead of Conway's cups apply usual penicillinic bottles or bottles with a semi-partition to separate introduction of test and alkali. For acceleration of diffusion of ammonia of a bottle place for 2 hours in the thermostat at 37 ° or use special rotators for continuous hashing of tests. As the receiver of ammonia serve the pieces of filter paper moistened to - that and suspended on a glass rod. From the reagents giving staining reaction with ammonia is more often than others use Ness's reactant of a ler (see. Nesslera reactant ), Indo-phenolic reactant, ninhydrin reactant and dikhlorizotsianuratny reactant.

1 ml of the studied test place the course of definition in a penicillinic bottle, there add 1 ml of saturated solution K 2 CO 3 . The bottle is quickly closed a rubber bung with the glass rod inserted into it moistened in 1 N solution H 2 S O 4 (apprx. 0,02 ml). For diffusion of ammonia of test leave to stand for the night at the room temperature. Upon termination of diffusion of a bottle open, traffic jams with glass rods transfer to pure penicillinic bottles with the measured amount of bezammiachny water (5 ml), vigorously stir up, add 0,5 ml of Nessler's reagent and kolorimetrirut with a length of light wave of 400 — 420 nanometers against check (without examinee of solution). For calculation of amount of ammonia prepare a standard curve, kolorimetriruya standard solutions (NH 4 ) 2 SO 4 . The method allows to define from 2 to 50 mkg of ammonia in test with an accuracy ± 0,5 mkg.

Quantity of the chemical reactants used during the carrying out definition of nitrogen K. the m, can change depending on character of the studied material.

Definition of nonprotein nitrogen K. the m is the most exact, but routine use in a wedge, laboratories does not find in the basic because of labor input. Usually To. the m serves for check of accuracy and correctness of other methods.



Bibliography: Biochemical methods of a research in clinic, under the editorship of A. A. Pokrovsky, page 77, M., 1969; Methods of modern biochemistry, under the editorship of V. L. Kretovich and K. F. Sholts, page 58, M., 1975; Modern methods in biochemistry, under the editorship of V. N. Aura-hovicha, page 17, M., 1977; Conway E. J. Microdiffusion analysis and volumetric error, L., 1962, bibliogr.

P. S. Krivchenkova.

Яндекс.Метрика