Dissolution 
711
—
Medium:
0.05 M pH 6.8 phosphate buffer (see Buffer solutions in the section Reagents, Indicators, and Solutions); 900 mL.
Apparatus 2:
50 rpm.
Time:
60 minutes.
Test solution—
If necessary, dilute a filtered portion of the solution under test with Medium to obtain a solution having a concentration of about 0.28 mg of erythromycin per mL, and mix.
Standard solution—
Dissolve an accurately weighed quantity of
USP Erythromycin RS in methanol (not more than 1 mL of methanol for each 14 mg of the Reference Standard), and dilute with water, quantitatively and with mixing, to obtain a stock solution containing about 0.56 mg per mL. Immediately prior to use, dilute the stock solution quantitatively with water to obtain a
Standard solution having a known concentration of about 0.28 mg per mL.
Procedure—
Transfer 5.0-mL portions of the
Test solution and the
Standard solution to separate 25-mL volumetric flasks, and treat each as follows: Add 2.0 mL of water, and allow to stand for 5 minutes with intermittent swirling. Add 15.0 mL of 0.25 N sodium hydroxide, dilute with
Medium to volume, and mix. Heat to 60
for 5 minutes, and allow to cool. Concomitantly determine the absorbances of these solutions at the wavelength of maximum absorbance at about 236 nm, with a suitable spectrophotometer, using blank solutions similarly prepared, except that 2.0 mL of 0.5 N sulfuric acid is substituted for the 2.0 mL of water. Calculate the amount of C
37H
67NO
13 dissolved.
Tolerances—
Not less than 70% (Q) of the labeled amount of C37H67NO13 is dissolved in 60 minutes.
Assay—
Place not less than 4 Tablets in a high-speed glass blender jar with 200 mL of methanol, and blend for 3 minutes. Add 300 mL of
Buffer No. 3, and blend for 3 minutes. Proceed as directed under
Antibiotics—Microbial Assays 81, using an accurately measured volume of this stock test solution diluted quantitatively with
Buffer No. 3 to yield a
Test Dilution having a concentration assumed to be equal to the median dose level of the Standard.
