Full resolution (JPEG) - On this page / på denna sida - XIV. Urine - II. Organic Physiological Constituents of Urine
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
ESTIMATION OF CREATININE. 697
acid the violet or purple-red color passes into’blue, which soon becomes pale
and finally a pale yellow color. It differs from the creatinine in color and
the absorption band as well as in that the creatinine reaction requires more
sodium oitroprusside.
The best method for preparing creatinine is the following, suggested
by Folin. 1
The creatinine is first precipitated as the double picrate
of creatinine and potassium by means of picric acid according to Jaffa’s
method, and then this precipitate, while still moist, is decomposed by
KHCO3 and water. The solution, which contains the creatinine besides
potassium carbonate and small amounts of impurities, is neutralized
with sulphuric acid and the sulphate precipitated by alcohol. The
creatinine is now converted into the double zinc-chloride salt and this
last treated with moist lead hydroxide. After the removal of the lead,
the solution contains a mixture of creatinine and creatine, which last is
completely transformed into creatinine by heating for forty-eight hours
with normal sulphuric acid. After exact neutralization with barium-
hydroxide solution it is concentrated to the point of crystallization.
According to recent work of Folin and Blanck the creatinine-zinc chloride
can be dissolved in warm 10 per cent sulphuric acid when creatinine-zinc alum
(C\H7 NsO) 2 SOiZnSOi, 8H2 is obtained and from this the creatinine can be
obtained by decomposing with barium acetate and removing the zinc by H2 S.
Creatine can, according to Folin and Denis, 2
be transformed into creatinine by
heating in an autoclave for 3 hours under a pressure of 4-5 kg. per qcm.
The quantitative estimation of creatinine used to be performed accord-
ing to Neubauer’s method for the preparation of creatinine, or more
simply by Salkowski’s 3
modification of this method. As this method
is now seldom used we refer the reader to other hand-books.
Folin 4
has suggested a colorimetric method for determining creatinine
which is based upon Jaffe’s picric-acid reaction and is as follows: 10
cc. of the urine are treated in a graduated flask of 500 cc. capacity
with 15 cc. of a 1.2 per cent solution of picric acid and 5 cc. of a 10
per cent NaOH solution. After shaking and allowing to stand for five
minutes it is diluted with water to 500 cc. and mixed. This solution
is now compared in a Duboscq colorimeter "with a 1/2 normal potassium-
dicromate solution. The latter solution has in a layer 8 mm. thick
exactly the same intensity of color as a layer 8.1 mm. thick of a solution
of 10 milligrams creatinine after the addition of 15 cc. picric-acid solu-
tion and 5 cc. NaOH solution and dilution to 500 cc. The calculations
are simple. For example, in case the urine tested in a layer 7.2 mm.
thick has the same color as the dichromate solution in a layer 8 mm.
thick, then the quantity of creatinine in 10 cc. of the urine will be
8 1
= ^2X10, or 11.25 milligrams. This method has been tried by many
authorities and found to be trustworthy.
1
Zeitschr. f. physiol. Chem., 41.
2
Folin and Blanck, Journ. of biol. Chem., 8, with Denis, ibid., 8.
3
Zeitschr. f. physiol. Chem., 10 and 14.
* Ibid., 41.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
