Identification—
To a quantity of powdered Tablets add a volume of methanol sufficient to yield a solution containing the equivalent of about 5 mg of erythromycin per mL. Shake this mixture by mechanical means for about 30 minutes. Centrifuge a portion of this mixture, and use the clear supernatant as the test solution. Prepare a Standard solution of
USP Erythromycin Stearate RS in methanol containing about 8 mg per mL. Apply separately 20 µL each of the test solution and the Standard solution to a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture, and allow to dry. Place the plate in an unlined chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of methanol and chloroform (85:15) until the solvent front has moved about 9 cm. Remove the plate from the chamber, mark the solvent front, and allow the solvent to evaporate. Spray the plate with a methanolic solution of 2
¢,7
¢-dichlorofluorescein (1 in 500), and examine the plate under long-wavelength UV light: the
RF values of the principal fluorescent spots obtained from the test solution correspond to those obtained from the Standard solution. Then spray the plate with a mixture of dehydrated alcohol,
p-methoxybenzaldehyde, and sulfuric acid (90:5:5). Heat the plate at 100
for 10 minutes, and examine the chromatograms, in which the erythromycin appears as a black-to-purple spot: the
RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Dissolution 711—
Medium:
0.05 M pH 6.8 phosphate buffer (see under Solutions in the section Reagents, Indicators, and Solutions); 900 mL.
Apparatus 2:
100 rpm.
Time:
120 minutes.
Stock standard solution—
Dissolve an accurately weighed quantity of
USP Erythromycin RS in methanol to obtain a solution containing about 14 mg per mL. Dilute quantitatively with water, and mix to obtain a solution having a known concentration of about 0.56 mg of
USP Erythromycin RS per mL.
Working standard solution—
On the day of use, dilute 25.0 mL of Stock standard solution with water to 50.0 mL, and mix.
Test solution—
After 120 minutes, withdraw a portion of the solution under test, filter, and dilute with Medium, if necessary, to obtain a solution having an estimated concentration of about 0.28 mg of erythromycin per mL.
Procedure—
Transfer 5.0-mL portions of the
Working standard solution to two 25-mL volumetric flasks, one of which serves as a working standard blank. Similarly, transfer 5.0-mL portions of the
Test solution to two 25-mL volumetric flasks, one of which serves as a blank for that
Test solution. To each of the flasks designated as a blank add 2.0 mL of 0.5 N sulfuric acid and to the remaining flasks add 2.0 mL of water. Allow to stand for 5 minutes with intermittent swirling. To all flasks add 15.0 mL of 0.25 N sodium hydroxide, dilute with
Medium to volume, and mix. Heat the flasks in a water bath at 60 ± 0.5
for 5 minutes, and allow to cool. Using a suitable spectrophotometer, determine the absorbance of each solution, corrected for its blank solution, at the wavelength of maximum absorbance at about 236 nm. Determine the amount of C
37H
67NO
13 dissolved from the
Test solution in comparison with the solution obtained from the
Working standard solution.
Tolerances—
Not less than 75% (Q) of the labeled amount of C37H67NO13 is dissolved in 120 minutes.
