Medium: 0.01Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Color reagent— Slowly,and with constant mechanical stirring,add 325mLof sulfuric acid to 173mLof cold water.Allow the solution to cool,add 2mLof ferric chloride solution (1in 40)and 1g ofp-dimethylaminobenzaldehyde,and stir to dissolve.Store in a low actinic flask.[NOTE—Prepare thisColor reagent on the day of use.]

Standard solution— Dissolve an accurately weighed quantity of USP Erythromycin RSinMedium to obtain a solution having a known concentration of about 0.44mg per mL,using sonication if necessary to dissolve.[NOTE—Use thisStandard solution within 5.5hours.]

Test solution— Pass a portion of the solution under test through a filter having a porosity of 0.5µm or less,discarding the first 5mLof the filtrate.Use the filtrate.

Procedure— To three separate 50-mLglass-stoppered conical flasks add 2.0mLofStandard solution,2.0mLofTest solution,and 2.0mLofMedium (to serve as theBlank),respectively.Place the flasks in an ice bath for about 15minutes.At precise 1-minute intervals add 10.0mLofColor reagentto theStandard solution,theTest solution,and theBlank,in turn.Immediately after adding theColor reagent,remove each flask from the ice bath,insert the stopper,mix,and allow to stand at room temperature for exactly 30minutes.Sequentially determine the absorbance at 480nm of theStandard solutionand theTest solutionat precise 1-minute intervals,using theBlank to set the spectrophotometer to zero.Calculate the quantity,in mg,of C37H67NO13equivalent dissolved by the formula: in whichCis the concentration,in mg per mL,of USP Erythromycin RSin theStandard solution,Pis the designated content,in µg per mg,of erythromycin in the USP Erythromycin RS,andAUandASare the absorbances of theTest solutionand theStandard solution,respectively.

Tolerances— Not less than 75%(Q)of the labeled amount of C37H67NO13equivalent is dissolved in 45minutes.

Arsenomolybdate stock solution— Dissolve 100g of ammonium molybdate in 1.7liters of water in a 2-liter volumetric flask.Slowly add,with mixing,84mLof sulfuric acid.Add 12g of sodium arsenate dissolved in 100mLof water.Dilute with water to volume,and mix.Store in an amber bottle for 24hours before using.[NOTE—This solution should not come in contact with rubber.]

Arsenomolybdate solution— Use a mixture of water andArsenomolybdate stock solution (2:1).[NOTE—Prepare fresh on the day of use.]

pH4.8Acetate buffer— Dissolve 133g of sodium acetate in about 3.5liters of water.Adjust with glacial acetic acid to a pHof 4.8±0.1,dilute with water to 4liters,and mix.

4.5M Sulfuric acid— [NOTE—This reagent is called out in theDiagram of Dissolution Test Method for Erythromycin Ethylsuccinate Tablets Labeled as ChewableunderAutomated Methods of Analysis á16ñ.]Add 1.5liters of water to a 2-liter volumetric flask,and place the flask in an ice bath.Slowly add,with stirring,300mLof sulfuric acid.Allow the solution to cool,dilute with water to volume,and mix.At the time of use,add 0.5g of sodium dodecyl sulfate to each liter.

Medium: 0.1Macetate buffer,pH5.0;900mL.

Apparatus 2: 75rpm.

Time: 60minutes.

Standard stock solution— Dissolve an accurately weighed quantity of USP Erythromycin RSinpH4.8Acetate buffer to obtain a solution having a known concentration of about 0.5mg per mL.

Standard solutions— Transfer 8.0-,4.0-,and 1.0-mLvolumes of theStandard stock solution to separate 100-mLvolumetric flasks,add 6.0mLof pH7.6phosphate buffer (see SolutionsunderReagents,Indicators,and Solutions)and 6.0mLofMedium to each flask,dilute withpH4.8Acetate buffer to volume,and mix to obtain solutions having known concentrations of about 40,20,and 5µg per mLof USP Erythromycin RS,respectively.

Procedure— Transfer 6.0mLof the solution under test to a 50-mLvolumetric flask,add 6.0mLof pH7.6phosphate buffer,and heat in boiling water for 30minutes.Cool to room temperature,and dilute withpH4.8Acetate bufferto volume.To determine the absorbance values,use an automated analyzer (illustrated in theDiagram of Dissolution Test Method for Erythromycin Ethylsuccinate Tablets Labeled as ChewableunderAutomated Methods of Analysis á16ñ)consisting of a liquid sampler;a proportioning pump;a manifold;and a spectrophotometer equipped with matched flow cells,suitable recording devices,and analysis capability at 660nm.Adjust the system until a steady baseline is achieved.Start the sampler,and conduct determinations at a rate of about 40to 60per hour with a 3:1(sample/wash)ratio.[NOTE—Adjust the analyzer flow rates if necessary to optimize system performance.]Determine the amount of C37H67NO13dissolved from the absorbance values of theTest solution and theStandard solutions.

Tolerances— Not less than 75%(Q)of the labeled amount of C37H67NO13is dissolved in 60minutes.