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176 271 Readily Carbonizable Substances Test / Chemical TestsUSP 37
271 READILY CARBONIZABLE
SUBSTANCES TEST
In tests for readily carbonizable substances, unless other-
wise directed, add the specified quantity of the substance,
finely powdered if in solid form, in small portions to the
comparison container, which is made of colorless glass re-
sistant to the action of sulfuric acid and contains the speci-
fied乎的组词 volume of sulfuric acid (see under Reagent Specifications
in the section Reagents, Indicators, and Solutions).
Stir the mixture with a glass rod until solution is complete,
allow the solution to stand for 15 minutes, unless otherwise
directed, and compare the color of the solution with that of
the specified Matching Fluid (see Color and Achromicity
631) in a comparison container, which also is of colorless
glass and has the same internal and cross-section dimen-
sions, viewing the fluids transversely against a background
of white porcelain or white glass.
When heat is directed in order to effect solution of the
substance in the sulfuric acid, mix the sample and the acid
in a test tube, heat as directed, and transfer the solution to
the comparison container for matching with the designated
Matching Fluid (see Color and Achromicity 631).
281 RESIDUE ON IGNITION
Portions of this general chapter have been harmonized
with the corresponding texts of the European Pharmacopoeia
and the Japanese Pharmacopoeia. The portions that are not
harmonized are marked with symbols (). The harmonized
u
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texts of these pharmacopeias are therefore interchangeable,
and the metho秋夕唐杜牧古诗 ds of the European Pharmacopoeia and/or the
Japanese Pharmacopoeia may be used for demonstration of
compliance instead of the present United States Pharmaco-
peia general chapter. These pharmacopeias have undertaken
not to make any unilateral change to this harmonized chap-
ter.
The Residue on Ignition/Sulfated Ash test uses a procedure
to measure the amount of residual substance not volatilized
from a sample when the sample is ignited in the presence of
sulfuric acid according to the procedure described below.
This test is usually used for determining the content of inor-
ganic impurities in an organic substance.
Procedure—Ignite a suitable crucible (for example, silica,
platinu描写夏雨的古诗 m, quartz, or porcelain) at 60050 for 30 minutes,
cool the 诗中含有梅花的诗句 crucible in a desiccator (silica gel or other suitable
desiccant), and weigh it accurately. Weigh accurately 1 to
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2g of the substance, or the amount specified in the indi-
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vidual monograph, in the crucible.
Moisten the sample with a small amount (usually 1 mL) of
sulfuric acid, then heat gently at a temperature as low as
practicable 七夕节又称什么 until the sample is thoroughly charred. Cool;
then,unless otherwise directed in the individual mono-
u
graph, moisten the residue with a small amount (usually 1
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mL) of sulfuric acid; heat gently until white fumes are no
longer evolved; and ignite at 60050, unless another
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temperature is specified in the individual monograph, until
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the residue is completely incinerated. Ensure that flames are
not produced at any time during the procedure. Cool the
crucible in a desiccator (青砖伴瓦漆《声声慢》 silica gel or other suitable desic-
cant), weigh accurately, and calculate the percentage of res-
idue.
Unless otherwise specified, if the amount of the residue so
obtained exceeds the limit specif舟夜书所见古诗朗读 ied in the individual mono-
graph, repeat the moistening with sulfuric acid, heating and
igniting as before, using a 30-minute ignition period, until
two consecutive weighings of the residue do not differ by
more than 0.5 mg or until the percentage of residue com-
plies with the limit in the individual monograph.
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Conduct the ignition in a well-ventilated hood, but pro-
tected from air currents, and at as low a temperature as is
possible to effect the complete combustion of the carbon. A
muffle furnace may be used, if desired, and its use is recom-
mended for the final ignition at 60050.
Calibration of the muffle furnace may be carried out using
an appropriate digital temperature meter and a working
thermocouple probe calibrated against a standard thermo-
couple traceable to the National Institute of Standards and
Technology.
Verify the accuracy of the measuring and controlling cir-
cuitry of the muffle furnace by checking the positions in the
furnace at the control set point temperature of intended
use. Select positions th四海无闲田 at reflect the eventual method of use
with respect to location of the specimen under test. The tol-
erance is 25 at each position measured.
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291 SELENIUM
Stock Solution—Dissolve 40.0 mg of metallic selenium
in 100 mL of dilute nitric acid (1 in 2) in a 1000-mL volu-
metric flask, warming gently on a steam bath if necessary to
effect solution, add water to volume, and mix. Pipet 5 mL of
this solution into a 200-mL volumetric flask, add water to
volume, and mix. Each mL of the resulting solution contains
the equivalent of 1 mg of selenium (Se).
Diaminonaphthalene Solution—Dissolve 100 mg of
2,3-diaminonaphthalene and 500 mg of hydroxylamine hy-
drochloride in 0.1 N hydrochloric acid to make 100 mL. Pre-
pare this solution fresh on the day of use.
Standard Solution—Pipet 6 mL of Stock Solution into a
150-mL beaker, and add 25 mL of dilute nitric acid (1 in 30)
and 25 mL of water.
Test Solution—Clean combustion of the test material is
an important factor in conducting the test. For compounds
that burn poorly and produce soot, the addition of magne-
sium oxide usually results in more thorough combustion
and reduces soot formation. Where the need to add magne-
sium oxide has been identified, it is specified in the individu-
al monograph. Using a 1000-mL combustion flask and using
25 mL of dilute nitric acid (1 in 30) as the absorbing liquid,
proceed as directed under Oxygen Flask Combustion 471,
using a test specimen weighing 100 to 200 mg, unless di-
rected otherwise in the individual monograph. Upon com-
Official from August 1, 2014
Copyright (c) 2014 The United States Pharmacopeial Convention. All rights reserved.