Packaging and storage—
Preserve in tight containers, at a temperature not exceeding 45
.
Labeling—
If benzene has been used in the manufacturing process, the name of the article will be Carbomer 934, Carbomer 934P, Carbomer 940, or Carbomer 941, whichever is appropriate. In addition, when benzene is used, the labeling requirements for the referenced individual Carbomer are applicable. If benzene is not used in the manufacturing process, label it to indicate whether it is Type A, B, or C; and also to state the measured viscosity, the solvent or solvents used in the polymerization process, and the nominal and residual solvent levels for each solvent.
Identification—
A:
Infrared Absorption 
197K
—The IR spectrum exhibits main bands at or near (±5) wave numbers (cm
-1) 1710, 1454, 1414, 1245, 1172, 1115, and 801, with the strongest band at 1710.
B:
Adjust a 1 in 100 dispersion of it with 1 N sodium hydroxide to a pH of about 7.5: a viscous gel is produced.
C:
Add 2 mL of a 1 in 10 aqueous solution of calcium chloride, while stirring, to 10 mL of the gel obtained from Identification test B: a white precipitate is immediately produced.
D:
Prepare a 1 in 100 dispersion of it. Add 0.5 mL of
thymol blue TS to 10 mL of the dispersion: an orange color is produced. To another 10 mL of the dispersion add 0.5 mL of
cresol red TS: a yellow color is produced.
Viscosity 911—
Carefully add 2.50 g of the resin, which has been previously dried, to 500 mL of water in a 800-mL beaker, while stirring continuously at 1000 ± 50 rpm. The stirrer shaft is set at an angle of 60
and positioned at one side of the beaker, and the propeller is positioned near the bottom of the beaker. The stirrer used should be a three-blade, 2-inch marine impeller. Add Carbomer Homopolymer at a uniform rate over a period of 45 to 60 seconds, being sure that loose aggregates of powder are broken up, and continue stirring at 1000 ± 50 rpm for 15 minutes.
[NOTE—Proper dispersion of the Carbomer Homopolymer resin is imperative for accurate viscosity readings.
] Remove the stirrer, and allow the beaker containing the dispersion to stand at controlled room temperature for 30 minutes. Insert a paddle stirrer to a depth necessary to ensure that the air is not drawn into the dispersion, and while stirring at 300 ± 25 rpm, titrate potentiometrically (see
Titrimetry 541) with sodium hydroxide solution (18 in 100) to the pH indicated on the label. (For example, if the pH is 7.3, then the total volume of sodium hydroxide would be about 5.4 mL.) After adding the sodium hydroxide solution, stir with a paddle mixer at 300 ± 25 rpm for 2 to 3 minutes.
[NOTE—After neutralization, care must be taken to avoid excessively high shearing, as aggressive mixing will break the polymer chains and reduce the viscosity reading.
] Take the final pH reading with a pH meter. If the final pH exceeds that indicated on the label, discard the mucilage, and prepare another using a smaller amount of sodium hydroxide for titration. Place the neutralized mucilage into a water bath maintained at 25 ± 2
for 1 hour, then perform the viscosity determination without delay.
Equip a suitable rotational viscometer (i.e., a Brookfield RVT or RVF viscometer) with a suitable spindle, as defined in the chart below. For spindle dimensions, consult the table under Carbomer Copolymer.
Expected
Viscosity (cP) |
Spindle Number |
Multiplier |
| 100–400 |
1 |
5 |
| 400–1600 |
2 |
20 |
| 1000–4000 |
3 |
50 |
| 2000–8000 |
4 |
100 |
| 4000–16,000 |
5 |
200 |
| 10,000–40,000 |
6 |
500 |
| 40,000–160,000 |
7 |
2000 |
With the spindle rotating at 20 rpm, observe and record the scale reading. Calculate the viscosity, in centipoise, by multiplying the scale reading by the multiplier defined in the table above for the spindle used at 20 rpm. The viscosity values, determined by the conditions specified herein, are within the limits specified in the accompanying table.
| Carbomer Homopolymer |
Viscosity Specified (cP) |
| A |
4,000–11,000 |
| B |
25,000–45,000 |
| C |
40,000–60,000 |
Loss on drying 731—
Dry it in vacuum at 80
for 1 hour: it loses not more than 2.0% of its weight.
Limit of ethyl acetate and cyclohexane—
[NOTE—This test is required only for those Carbomer Homopolymers whose labeling indicates that ethyl acetate or a mixture of ethyl acetate and cyclohexane was used in the polymerization process.
]
Standard stock solution—
Transfer 5.0 mL of methanol to a 10-mL serum vial, insert a rubber septum, and seal with a metal cap. Add an accurately weighed quantity of about 25.0 µL of ethyl acetate and 20.0 µL of cyclohexane through the septum into the vial, and mix.
Standard solution—
Transfer 20.0 mL of methanol to a 30-mL serum vial, insert a rubber septum, and seal with a metal cap. Through the rubber septum, add 10 µL of methyl ethyl ketone (internal standard) and 50.0 µL of the Standard stock solution, and mix.
Test solution—
Transfer about 50 mg of Carbomer Homopolymer, accurately weighed, to a 30-mL serum vial, add 20 mL of methanol, insert a rubber septum, and seal with a metal cap. Through the rubber septum, add 10 µL of methyl ethyl ketone, and mix.
Procedure—
Proceed as directed under
Carbomer Copolymer, except to calculate the percentages of ethyl acetate and cyclohexane in the portion of Carbomer Homopolymer taken by the formula:
100(WS / WT)(RU / RS)
in which
WS is the weight, in mg, of ethyl acetate or cyclohexane, as appropriate, in the
Standard solution; WT is the weight, in mg, of Carbomer Homopolymer taken to prepare the
Test solution; and
RU and
RS are the peak area ratios of the relevant analyte peak to the methyl ethyl ketone peak obtained from the
Test solution and the
Standard solution, respectively: not more than 0.5% of ethyl acetate and not more than 0.3% of cyclohexane is found.
Limit of benzene—
[NOTE—This test does not apply to those articles titled
Carbomer 934,
Carbomer 934P,
Carbomer 940 or
Carbomer 941. Those articles meet the requirements for
Limit of benzene in their respective individual monographs.
]
Solvent solution—
Quantitatively dissolve an accurately weighed quantity of benzene in dimethyl sulfoxide to obtain a solution having a concentration of about 1.0 mg per mL. Dilute this solution quantitatively, and stepwise if necessary, with organic-free water (see
Organic Volatile Impurities 467) to obtain a solution having a concentration of about 0.1 µg per mL.
Test solution—
Transfer about 50 mg of Carbomer Homopolymer, accurately weighed, to a 10-mL volumetric flask. Add about 7.5 mL of sodium chloride solution (2 in 100), and mix by mechanical means until homogeneous (usually about 30 minutes). Dilute with sodium chloride solution (2 in 100) to volume, and mix until homogeneous (usually less than 1 minute). [Note—This preparation must be analyzed within 3 hours of preparation.]
Reference solution—
Transfer about 50 mg of Carbomer Homopolymer, accurately weighed, to a 10-mL volumetric flask. Add about 7.5 mL of sodium chloride solution (2 in 100), and mix by mechanical means until homogeneous (usually about 30 minutes). Add 1.0 mL of the Solvent solution, dilute with sodium chloride solution (2 in 100) to volume, and mix until homogeneous (usually less than 1 minute). This solution contains about 0.01 µg of benzene per mL.
Chromatographic system—
Proceed as directed in the test for Limit of benzene under Carbomer Copolymer.
Procedure—
Proceed as directed in the test for
Limit of benzene under
Carbomer Copolymer. Calculate the percentage of benzene in the portion of Carbomer Homopolymer taken by the formula:
(C/W)(rU / rS)
in which
C is the concentration, in µg per mL, of benzene in the
Reference solution; W is the weight, in mg, of Carbomer Homopolymer taken to prepare the
Test solution; and
rU and
rS are the benzene peak responses obtained from the
Test solution and the
Reference solution, respectively: not more than 0.0002% is found.
Limit of acrylic acid—
0.01 M Phosphate buffer—
Dissolve 1.361 g of monobasic potassium phosphate in 100 mL of water, and mix.
Solution A—
Use 0.01 M Phosphate buffer.
Solution B—
Prepare a filtered and degassed mixture of 0.01 M Phosphate buffer and acetonitrile (1:1, v/v).
Mobile phase—
Use variable mixtures of
Solution A and
Solution B as directed for
Chromatographic system. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Solvent—
Dissolve 25 g of potassium alum in 1000 mL of water, and mix.
Standard solution—
Dissolve an accurately weighed quantity of acrylic acid in the Solvent, and dilute quantitatively, and stepwise if necessary, to obtain a solution having a concentration of about 12.5 µg per mL.
Test solution—
Mix about 100 mg of Carbomer Homopolymer, accurately weighed, with
Solvent, and add
Solvent to obtain 20.0 mL of suspension. Heat the suspension at 50
for 20 minutes with occasional shaking. Then shake the suspension continuously at room temperature for 60 minutes. Centrifuge and use the clear supernatant.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 205-nm detector and a 4.6-mm × 12-cm column that contains packing L1. The flow rate is about 1 mL per minute. The chromatograph is programmed as follows.
Time
(minutes) |
Solution A
(%) |
Solution B
(%) |
 Elution |
| 0 |
100 |
0 |
equilibration |
| 0–8 |
100 |
0 |
isocratic |
| 8–9 |
100®0 |
0®100 |
linear gradient |
| 9–20 |
0 |
100 |
isocratic |
| 20–21 |
0®100 |
100®0 |
linear gradient |
| 21–30 |
100 |
0 |
isocratic |
Chromatograph the
Standard solution, and record the peak responses as directed for
Procedure: the relative standard deviation for replicate injections is not more than 5%.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the response for the acrylic acid peaks. Calculate the percentage of free acrylic acid in the portion of Carbomer Homopolymer taken by the formula:
(C/W)(rU / rS)
in which
C is the concentration, in µg per mL, of acrylic acid in the
Standard solution; W is the weight, in mg, of Carbomer Homopolymer taken to prepare the
Test solution; and
rU and
rS are the acrylic acid responses obtained from the
Test solution and the
Standard solution, respectively: not more than 0.25% is found.
Content of carboxylic acid—
Proceed as directed in the test for
Content of carboxylic acid under
Carbomer Copolymer, except to calculate the percentage of carboxylic acid in the portion of Carbomer Homopolymer taken by the formula:
100(45.02VN/W)
in which
W is the weight, in mg, of the portion of Carbomer Homopolymer taken; and the other terms are as defined therein.
Carbomer Homopolymer