TDS-231 Separation of Carbopol® Polymers from ... - Lubrizol

TECHNICAL DATA SHEET
TDS-231
Edition: September 27, 1995
Separation of Carbopol ® Polymers from
Complex Formulations for Quantitative Analysis
There are three major possible scenarios related to
separating Carbopol ® polymers from a formulation for
analysis:
A) The ingredients are all soluble 1 in water and
alcohol.
B) The ingredients are all insoluble in alcohol
(with the exception of the Carbopol polymer).
C) Some of the ingredients are soluble in alcohol,
while some are insoluble.
There is a significant difference in the solubility of
Carbopol polymers which are “soluble” (fully
swellable) in alcohol (such as methanol or ethanol);
whereas, the sodium, potassium, and ammonium salts
are completely insoluble (non-swelling). Assuming
that there are very few other formulation ingredients
which show this extreme variation with simple pH
adjustment in alcohol, the following discussion will
suggest an appropriate analysis scheme based on the
use of alcohol alone or with small additions of either
hydrochloric acid or ammonium hydroxide, as
appropriate. The choice of hydrochloric acid and
ammonium hydroxide is based on the fact that any
excess added will be fugitive and can be evaporated
away after the appropriate separations have been
made. Ethanol will be used in the following
discussions.
1 NOTE: Carbopol poly mers are three-dimensional, crosslinked structures, and as such
are not soluble in w ater or other solvents. The word “soluble”, as used in this
data sheet, more accurately describes the degree of swelling of the poly mer in
the solv ent.
A) Case I: All ingredients are soluble in
alcohol.
The formulation is diluted with alcohol (containing
~0.25% hydrochloric acid if the pH is over 4-5) until
the ethanol content is at least 50%, and preferably
75%, (the remainder probably being mostly water)
and where the probable Carbopol polymer
concentration is below 0.25%. Here the Carbopol
polymer is in the swelled state and the formulation
is a single phase. When ammonium hydroxide is
added (to a pH of below 8), the Carbopol polymer
will precipitate as fine, non-swollen particles which
can be separated by filtration or centrifugation
followed by a washing in alcohol (containing ~0.5%
ammonium hydroxide). The Carbopol polymer,
when dried, can be quantitatively analyzed by
titration. It will be in the form of a partial ammonium
salt, depending on the drying conditions.
The appropriate equivalent weight of the partial
ammonium salt of Carbopol polymer must be
separately determined using this same procedure
but using Carbopol mucilage of known concentration
as a blank. The equivalent weight thus
determined should be in the range of 75 (if all the
ammonia is liberated) to 92 (if no ammonia is
liberated). In the absence of a blank, and where
extreme accuracy is not needed, a value of 79 can
be used. Some experiments will be needed to
establish concentrations of ammonium hydroxide
and hydrochloric acid and the ratio of alcohol to
water at all stages so that ammonium chloride
remains in solution and does not accompany the
Carbopol polymer in the precipitate phase. The
Carbopol polymer salts will remain as non-swelling
precipitates where the concentration of ethanol in
water exceeds roughly 37%. Thus, to be safe, the
alcohol content should exceed 50% and some
water may be needed to keep the ammonium
chloride in solution. These same comments apply
to the cases that follow.
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B) Case II: All ingredients (except
Carbopol polymer) are alcohol
insoluble.
A large excess of alcohol is added to the
formulation so that the Carbopol polymer
concentration is less than 0.25% and the other
ingredients are insoluble. To insure that the
Carbopol polymer is fully swellable, the alcohol
used contains about 0.25% hydrochloric acid. The
insoluble formulation ingredients are separated out
by filtration or centrifugation. The dilute solution is
stirred while about 0.5% ammonium hydroxide is
added to the system (addition as a water solution is
permissible). The Carbopol polymer will precipitate
as fine white particles that can be separated and
treated as in Case I above.
C) Case III: Some formulation ingredients
are alcohol soluble while
others are not.
This situation may represent the majority of cases
and will require an additional step. Here we assure
that the Carbopol polymer is initially fully alcohol
swellable by adding hydrochloric acid to reduce the
pH below 3 and adding alcohol until 50% (or
preferably 75%) concentration is reached and the
concentration of Carbopol polymer is below 0.25%.
The diluted formulation is then centrifuged or
filtered to effect separation of the insoluble
ingredients followed by washing, etc. The diluted
solution phase (including the washing) contains
alcohol soluble ingredients and swelled Carbopol
polymer. It should then be treated by adding
ammonium hydroxide to the system and
proceeding as in Case I.
TDS-231
Separation of Carbopol ® Polymers from Complex
Formulations for Quantitative Analysis
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TDS-231
Separation of Carbopol ® Polymers from Complex
Formulations for Quantitative Analysis
Page 3 of 3
Separation of Carbopol ® Polymers from Complex
Formulations for Quantitative Analysis (Flow Chart)
Formulation Ingredients
Soluble in water and alcohol Insoluble in alcohol*
(*Note: Carbopol ® polymer is
soluble)
Dilute with excess alcohol
(50-75%) (~pH 3-4)
[Carbopol ® polymer
concentration