(kar' boe mer).
(Any article currently titled Carbomer 934P that is manufactured without the use of benzene will be officially titled Carbomer Homopolymer after January 1, 2011, and will meet the requirements of the new Carbomer Homopolymer monograph after January 1, 2007.)
» Carbomer 934P is a high molecular weight polymer of acrylic acid cross-linked with allyl ethers of sucrose or pentaerythritol. Carbomer 934P, previously dried in vacuum at 80 for 1 hour, contains not less than 56.0 percent and not more than 68.0 percent of carboxylic acid (COOH) groups. The viscosity of a neutralized 0.5 percent aqueous dispersion of Carbomer 934P is between 29,400 and 39,400 mPa·s. [noteEffective January 1, 2011, the heading of this monograph will no longer constitute the official title for Carbomer 934P manufactured without the use of benzene. When benzene is not used in the manufacturing process, the name of the article will be Carbomer Homopolymer and will meet the requirements of the Carbomer Homopolymer monograph. ]
Packaging and storage Preserve in tight containers. No storage requirements specified.
Labeling A carbomer homopolymer manufactured using benzene and complying with the unique requirements of this monograph will be officially titled Carbomer 934P and will not be referred to as Carbomer Homopolymer.
A: Prepare a 1 in 100 dispersion of it. To one portion of the dispersion add thymol blue TS: an orange color is produced. To another portion of the dispersion add cresol red TS: a yellow color is produced.
B: Adjust a 1 in 100 dispersion of it with 1 N sodium hydroxide to about pH 7.5: a very viscous gel is produced.
Viscosity 911 Carefully add 2.50 g, previously dried in a vacuum at 80 for 1 hour, to 500 mL of water in a 1000-mL beaker, while stirring continuously at 1000 ± 10 rpm, with the stirrer shaft set at an angle of 60 and to one side of the beaker, with the propeller positioned near the bottom of the beaker. Allow 45 to 90 seconds for addition of the test preparation at a uniform rate, being sure that loose aggregates of powder are broken up, and continue stirring at 1000 ± 10 rpm for 15 minutes. Remove the stirrer, and place the beaker containing the dispersion in a 25 ± 0.1 water bath for 30 minutes. Insert the stirrer to a depth necessary to ensure that air is not drawn into the dispersion, and, while stirring at 300 ± 10 rpm, titrate (see Titrimetry 541) with a calomel-glass electrode system to a pH of between 7.3 and 7.8 by adding sodium hydroxide solution (18 in 100) below the surface, determining the endpoint potentiometrically. Stir for 2 to 3 minutes until neutralization is complete. Then determine the final pH. [noteIf the pH is below 7.3, raise it with additional sodium hydroxide. If it is above 7.8, discard the mucilage, and prepare another using a smaller amount of sodium hydroxide for titration. ] Return the neutralized mucilage to the 25 water bath for 1 hour. Measure the pH again and make certain that the mucilage pH is between 7.3 and 7.8. Perform the viscosity determination without delay to avoid slight viscosity changes that occur 75 minutes after neutralization. Equip a suitable rotational viscometer with a spindle having a cylinder 1.5 cm in diameter and 0.2 cm high attached to a shaft 0.3 cm in diameter, the distance from the top of the cylinder to the lower tip of the shaft being 3.02 cm.1 The spindle rotates at 20 rpm at an immersion depth of 4.9 cm. Follow the instrument manufacturer's directions to measure the apparent viscosity: the viscosity is between 29,400 and 39,400 mPa·s.
Loss on drying 731 Dry it in vacuum at 80 for 1 hour: it loses not more than 2.0% of its weight.
Heavy metals, Method II 231: 0.002%.
Limit of benzene
Standard solution Quantitatively dissolve an accurately weighed quantity of benzene in methanol to obtain a solution having a known concentration of about 0.2 mg per mL. Quantitatively dilute this solution with organic-free water (see Residual Solvents 467) to obtain a solution having a known concentration of about 1.0 µg per mL.
Test solution Transfer about 1 g of Carbomer 934P, accurately weighed, to a 100-mL volumetric flask. Add about 75 mL of sodium chloride solution (2 in 100), and mix by mechanical means until homogenous (usually about 30 minutes). Dilute with sodium chloride solution (2 in 100) to volume, and mix until homogenous (usually less than 1 minute). [noteThis preparation must be analyzed within 3 hours of preparation. ]
Chromatographic system (see Chromatography 621) The gas chromatograph is equipped with a flame-ionization detector, a 0.53-mm × 30-m fused silica analytical column coated with a 3.0-µm G43 stationary phase, a 0.53-mm × 5-m silica guard column deactivated with phenylmethyl siloxane, and a splitless injection system. The carrier gas is helium flowing at a linear velocity of about 35 cm per second. The injection port and detector temperatures are maintained at 140 and 260, respectively. The column temperature is programmed according to the following steps: it is held at 40 for 20 minutes, then increased rapidly to 240, and maintained at 240 for 20 minutes. Chromatograph the Standard solution, and record the responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 15%.
Procedure Separately inject equal volumes (about 1 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the benzene peaks. Calculate the percentage of benzene in the portion of Carbomer 934P taken by the formula:
10(C/W)(rU / rS)in which C is the concentration, in µg per mL, of benzene in the Standard solution; W is the weight, in mg, of Carbomer 934P taken to prepare the Test solution; and rU and rS are the benzene peak responses obtained from the Test solution and the Standard solution, respectively: not more than 0.01% is found.
Assay for carboxylic acid content Slowly add about 400 mg previously dried and accurately weighed, to 400 mL of water in a 1000-mL beaker, while stirring continuously at about 1000 rpm, with the stirrer shaft set at an angle of 60 and at the side of the beaker, with the propeller positioned near the bottom of the beaker, and continue stirring for 15 minutes. Reduce the stirring speed, and titrate potentiometrically with 0.25 N sodium hydroxide VS, using a calomel-glass electrode system. Allow 1 minute for mixing, after each addition of 0.25 N sodium hydroxide VS, before recording the pH. Calculate the carboxylic acid content as a percentage of carboxylic acid groups taken by the formula:
100(45.02VN/W)in which V is the volume, in mL, of sodium hydroxide consumed; N is the normality of the sodium hydroxide solution; W is the weight, in mg, of specimen taken; and 45.02 is the molecular weight of the carboxylic acid (COOH) group.
1 Available as an RV6 spindle from Brookfield, or the equivalent.