test procedure of purity
35. Procedure
35.1 Weigh 3 g to 5 g of the sample into a tared low-form,
65-mm diameter glass weighing dish fitted with a cover. Dry to
constant mass at 105 °C 6 1 °C in either a gravity or a
mechanical convection oven. Weigh at the end of an initial 2 h
heating period, then continue with 30-min heating periods until
the change in mass during a 30-min heating period is not more
than 0.10 %. If there is an increase in mass of the sample
during one or more drying periods, record the lowest mass
observed as the mass for use in the calculation of moisture
content. Calculate the loss in mass as the percent of moisture in
the sample.
35.2 Weigh 3 g 6 0.1 g of the sample, in the “as-received”
condition, to the nearest 0.001 g and transfer to a 400-mL
beaker.
35.3 Add 150 mL of ethanol (80 %) that has been heated to
between 60 °C and 65 °C, and immediately place the beaker in
a constant-temperature water bath maintained at 60 °C to
65 °C. The level of the water in the bath should be somewhat
higher than the level of the liquid in the beaker. Cover the
beaker as completely as possible with a lid that will permit
mechanical stirring. Lower a mechanical stirrer almost to the
bottom of the beaker, and stir for 10 min at a rate suitable to
provide good agitation without spattering material on the walls
of the beaker above the liquid level.
35.4 Stop the stirrer. Allow the undissolved matter to settle
with the beaker still in the bath, and then decant the hot
supernatant liquid as completely as possible through a tared,
fritted-glass filtering crucible.
35.5 Add 150 mL of ethanol (80 %), at 60 °C to 65 °C to the
beaker and proceed in accordance with 32.3 and 32.4.
35.6 After decanting the supernatant liquid as completely as
possible, transfer the insoluble matter to the crucible with the
aid of ethanol (80 %) at 60 °C to 65 °C in a wash bottle, being
careful to scrape all insoluble matter from the lid, the stirrer,
and the beaker. A total of about 250 mL of ethanol (80 %) will
normally be required to transfer the insoluble matter to the
crucible and to further wash the insoluble matter in the
crucible. During the operations prescribed in this paragraph,
apply suction only while filtration is in progress. Make every
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effort to avoid drying-out of the filter cake. If fines appear to
pass through the filter, use only gentle suction.
35.7 Wash the residue in the crucible with 50 mL of ethanol
(95 %) at room temperature, and finally with several portions
of ether at room temperature (Note 7). Without permitting
suction to continue longer than necessary, place the crucible in
a beaker or weighing bottle on the steam bath until no odor of
ether can be detected.
NOTE 7—Thorough washing with ether is necessary to remove ethanol
completely from the insoluble matter. If ethanol is not completely
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removed before oven drying, it may not be completely removed during the
oven drying.
35.8 Place the crucible in an oven at 105 °C 6 1 °C for 1 h.
Stir the contents of the crucible with a dissecting needle or thin
rod (preferably of smooth-surfaced metal) to break up the cake
and facilitate complete drying. Again, dry at 105 °C 6 1 °C for
1 h. Place the crucible in a desiccator. Cover it with a flat glass
plate, weighing bottle cover, or other suitable cover to mini-
mize absorption of moisture from the atmosphere in the
desiccator; and cool to room temperature (at least 30 min).
Weigh the uncovered crucible as rapidly as possible.
35.9 Dry the crucible for additional 1 h periods until the
change in mass during a 1-h drying period does not exceed
0.003 g. If increases in mass are observed after such additional
drying periods, record the lowest mass observed as the mass of
the crucible plus dry sodium carboxymethylcellulose.
36. Calculation
36.1 Calculate the percent sodium carboxymethylcellulose,
S, on the dry basis as follows:
S 5 ~A 310000!/~B ~100 2 C!!
(9)
where:
A
= mass of dried residue, g,
B
= mass of specimen used, g, and
C
= moisture in the specimen as received, %.
Sales Manager|carboxymethyl cellulose(CMC)
1 年we assure the purity of our product to our customer