About Sodium Carboxymethyl Celulose ( NaCMC )

SODIUM CARBOXYMETHYL CELLULOSE

SYNONYMS

Sodium cellulose glycolate, Na CMC, CMC, cellulose gum, sodium CMC;
INS No. 466
DEFINITION

Prepared from cellulose by treatment with alkali and monochloro-acetic
acid or its sodium salt. The article of commerce can be specified further by
viscosity.
Chemical names Sodium salt of carboxymethyl ether of cellulose
C.A.S. number 9004-32-4
Chemical formula [C6H7O2(OH)x(OCH2COONa)y]n
where
n is the degree of polymerization
x = 1.50 to 2.80
y = 0.2 to 1.50
x + y = 3.0
(y = degree of substitution)

Structural formula
where R = H or CH2COONa
Formula weight Structural unit with a degree of substitution of 0.20: 178.14
Structural unit with a degree of substitution of 1.50: 282.18
Macromolecules: greater than about 17,000 (n about 100)
Assay Not less than 99.5% of sodium carboxymethyl cellulose, calculated on the
dried basis

DESCRIPTION

White or slightly yellowish, almost odourless hygroscopic granules, powder
or fine fibres

FUNCTIONAL USES

Thickening agent, stabilizer, suspending agent

CHARACTERISTICS

IDENTIFICATION
Solubility (Vol. 4) : Yield viscous colloidal solution with water; insoluble in ethanol
Foam test                 : Vigorously shake a 0.1% solution of the sample. No layer of foam appears.
This test distinguishes sodium carboxymethyl cellulose from other cellulose
ethers and from alginates and natural gums.
Precipitate formation  :  To 5 ml of an 0.5% solution of the sample add 5 ml of a 5% solution of
copper sulfate or of aluminium sulfate. A precipitate appears. (This test
permits the distinction of sodium carboxymethyl cellulose from other
cellulose ethers, and from gelatine, carob bean gum and tragacanth gum).
Colour reaction     :  Add 0.5 g of powdered carboxymethylcellulose sodium to 50 ml of water,
while stirring to produce a uniform dispersion. Continue the stirring until a
clear solution is produced. To 1 ml of the solution, diluted with an equal
volume of water, in a small test tube, add 5 drops of 1-naphthol TS. Incline
the test tube, and carefully introduce down the side of the tube 2 ml of
sulfuric acid so that it forms a lower layer. A red-purple colour develops at
the interface.
PURITY
Loss on drying (Vol. 4)   :  Not more than 12% after drying (105o, to constant weight)
pH                                            : (Vol. 4) 6.0 – 8.5 (1 in 100 soln)
Sodium (Vol. 4)                  : Not more than 12.4% on the dried basis
Determine total sodium content by Atomic Absorption Spectroscopy or Flame Photometry
Sodium chloride                :  Not more than 0.5% on the dried basis
See description under TESTS
Free glycolate                    :  Not more than 0.4% calculated as sodium glycolate on the dried basis
See description under TESTS
Degree of substitution    :  Not less than 0.20 and not more than 1.50
See description under TESTS
Lead (Vol. 4)                       : Not more than 2 mg/kg
Determine using an atomic absorption technique appropriate to the
specified level. The selection of sample size and method of sample
preparation may be based on the principles of the method described in
Volume 4, “Instrumental Methods.”
TESTS

PURITY TESTS
Sodium chloride

Heat 5 g of the sample, weighed to the nearest 0.1 mg, in a platinum or porcelain crucible, first with a small flame so that the sample does not ignite and then, when the charring is complete, heat further in an electric oven for 15 min at about 500o. After cooling, pulverize the ashes thus obtained and extract several times with warm water. Filter the extracts into a 500-ml volumetric flask, acidify with nitric acid and dilute to the mark. Determine the NaCl content of 100 ml of this extract by the method of Volhard, using 0.02 N silver nitrate and 0.02 N ammonium thiocyanate. Each ml of 0.02 N silver nitrate is equivalent to 1.169 mg of NaCl. Calculate the sodium
chloride content by the formula:
where
a = ml of 0.02 N silver nitrate used
b = dry weight of 5 g of the sample
Free glycolate

Weigh 0.5 g of the sample to the nearest 0.1 mg, and transfer to a 100-ml beaker. Moisten the sample thoroughly with 5 ml of glacial acetic acid, followed by 5 ml of water, and stir with a glass rod until the solution is
complete (usually about 15 min are required). Slowly add 50 ml of acetone
while stirring and then approximately 1 g of sodium sulfate. Continue the
stirring for several min to ensure complete precipitation of the carboxymethyl cellulose. Filter through a soft, open-texture paper, previously wetted with a small amount of acetone, and collect the filtrate in a 100-ml volumetric flask. Use 30 ml of acetone to facilitate the transfer of the solids and to wash the filter cake. Make up to volume with acetone and mix.
Prepare a blank solution containing 5 ml of water, 5 ml of glacial acetic acid
and acetone in another 100-ml volumetric flask. Pipet 2 ml of the sample
solution and 2 ml of the blank solution into two 25-ml volumetric flasks.
Remove the acetone by heating the uncovered flasks upright in a boiling
water bath for exactly 20 min. Cool to room temperature and add 5 ml of
naphthalenediol TS, mix thoroughly, then add 15 ml more of the TS and
mix. Cover the mouth of the flask with a small piece of aluminium foil and
heat upright in the boiling water bath for 20 min. Cool to room temperature
and make up to volume with naphthalenediol TS.
Measure the absorbance of sample solution against blank solution at 540
nm using 1-cm cells. Read the corresponding mg of glycolic acid from the
calibration curve obtained as follows:
Introduce 0, 1, 2, 3 and 4-ml aliquots of standard glycolic acid solution (1
mg per ml, prepared by weighing accurately 0.100 g of glycolic acid,
previously dried in a vacuum desiccator for at least 16 h, and then
dissolving in 100 ml of water; do not keep the solution longer than 30 days)
into a series of five 100-ml volumetric flasks. Add water to each flask to a
volume of 5 ml, then add 5 ml of glacial acetic acid and make up with acetone to mark and mix. Pipet 2 ml of each solution (containing,
respectively, 0, 1, 2, 3, and 4 mg of glycolic acid per 100 ml) into a series of
five 25-ml volumetric flasks and proceed in the same manner as described
for the Test Solution. Plot the mg of glycolic acid in the original 100 ml of
solution against absorbance to give a calibration curve.
Calculate the sodium glycolate (free glycolate) content by the formula:
where
a = mg of glycolic acid read from the calibration curve
b = g of dry-weight of the sample

Degree of substitution

Sample preparation
Weigh 5 g of the sample to the nearest 0.1 mg, and transfer into a 500-ml
conical flask. Add 350 ml of methanol or ethanol (80% by volume). Shake
the suspension mechanically for 30 min. Decant through a tared glass
filtering crucible under gentle suction. Avoid, at the end of the decanting,
suction of air through the crucible. Repeat the treatment with the extraction
liquid until the test for chloride ions with a solution of silver nitrate TS is
negative. Normally three treatments are sufficient. Transfer the sodium
carboxymethyl cellulose into the same crucible. Displace the extraction
liquid that adheres to the substance with acetone. Dry the crucible in an
oven at 110o until constant in weight. Weigh the first time after 2 h. Cool the
crucible every time in a desiccator and pay attention during weighing to the
fact that sodium carboxymethyl cellulose is slightly hygroscopic.

Procedure
Weigh 2 g, to the nearest 0.1 mg, of the bone dry substance, obtained with
the above-mentioned alcohol-extraction procedure, in a tared porcelain
crucible. Initially, char carefully with a small flame and afterwards for 10
min, with a large flame. Cool and then moisten the residue with 3-5 ml of
concentrate sulfuric acid. Heat cautiously until the fuming is finished. After
some cooling add about 1 g of ammonium carbonate, distributing the
powder over the whole contents of the crucible. Heat again, initially with a
small flame until the fuming is finished and heat then at a dull red heat for
10 min. Repeat the treatment with sulfuric acid and ammonium carbonate if
the residual sodium sulfate still contains some carbon. Cool the crucible in
a desiccator and weigh. Instead of adding ammonium carbonate and
heating further with a flame, the crucible can be placed for 1 h in an oven at
about 600o.
Calculate the sodium content of the alcohol-extracted sample by the
formula:

where
a = weight of residual sodium sulfate
b = weight of the alcohol-extracted dry sample Calculate the degree of substitution by the formula:

METHOD OFASSAY
Calculate the percentage of sodium carboxymethyl cellulose in the sample
by subtracting from 100% the sum of the percentages of sodium chloride
and sodium glycolate (free glycolate), determined separately by the
procedures above.

13 October 2012 at 02.28 1 comment


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