アンモニア微量定量法
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概要
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The colorimetric method of van Slyke and Hiller, Borsook and Russell for ammonia estimation is simplified byusing commercial antiformine instead of potassium hypochlorite solution. And the reaction for indophenol formation is carried out in sodium bicarbonate and carbonate mixture in order to keep the solution possibly at the same pH. Test-tubes of 1,5 cm 10,0 cm and graduated at 10 ml. are used. To 1 ml. of test solution of unknown ammonia concentration in a test-tube immersed in ice-water are added successively and shaking each time 2 ml. of 5 % phenol, 1 ml. of saturated sodium bicarbonate and 3 ml. of antiformine-soda solution. The last solution consists of two volumes of commercial antiformine and one volume of 10.6% sodium carbonate. The mixture in the test-tube is left at the room temperature for 20 minutes, filled up with water to the 10 ml.-mark and photometrized (Pulfrichs photometer, filter S 61). As to the presence of a negligible contamination of ammonia in the reagents, 1 ml. of water instead of the test solution may be treated in the above mentioned way and the solution serves as control of the test solution. When 1 ml of ammonia sulfate solution is used extinction coefficient of the blue solution is proportional to the ammonia concentration within the range of M/1000-M/8000. Since, however, the, absolute value of extinction may vary owing to alteration of the antiformine reagent, 1 ml of M/1000 ammonium sulfate must be colorized simultaneously in the way mentioned above for the purpose of calculation of ammonia concentration in the unknown solution. E.(10mm) of the indophenol solution out of 1 ml. of M/1000 ammonium sulfate is, in general, 0.6-0.8. The calculation of ammonia content of the test solution is as follows. ammoia γ=E. of the test.solution-E. of the control./E. of the standard solution-E. of the control.×28 γ The method can not be applied directly to a biological fluid, because protein, but amino acids show also indophenol formation to a more or less extent. Therefore distillation of ammonia should be carried out previously and the diffusion cell of Conway is very convenient as it will be reported in the next communication on the micromethod for estimation of blood urea.
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