Packaging and storage
Preserve in tight containers.
Add the following:
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
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.
Adjust a 1 in 100 dispersion of it with 1 N sodium hydroxide to about pH 7.5: a very viscous gel is produced.
Carefully add 2.50 g, previously dried in 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 ± 0.2
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. The total volume of sodium hydroxide solution (18 in 100) used is about 6.2 mL. Allow 2 to 3 minutes before final pH determination. [NOTE
If the final pH exceeds 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, then perform the viscosity determination without delay to avoid slight viscosity changes that occur 75 minutes after neutralization. Equip a suitable rotational viscosimeter with a spindle having a cylinder 1.47 cm in diameter and 0.16 cm high attached to a shaft 0.32 cm in diameter, the distance from the top of the cylinder to the lower tip of the shaft being 3.02 cm, and the immersion depth being 4.92 cm (No. 6 spindle). With the spindle rotating at 20 rpm, observe and record the scale reading. Calculate the viscosity, in centipoises, by multiplying the scale reading by the constant for the spindle used at 20 rpm.
Loss on drying 731
Dry it in vacuum at 80
for 1 hour: it loses not more than 2.0% of its weight.
Change to read:
Limit of benzene
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 Organic Volatile Impurities 467
) to obtain a solution having a known concentration of about 1.0 µg per mL.
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
, 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.NF24
Chromatograph the Standard solution,
and record the responses as directed for Procedure:
the relative standard deviation for replicate injections is not more than 15%.
Separately inject equal volumes
(about 1 µL)NF24
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;
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:
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.