Test specimen— Extract a volume of Injection,equivalent to about 2.5mg of carboprost tromethamine,with 1.5to 2times its volume of chloroform.Discard the chloroform layer,and acidify the aqueous layer with 3to 5drops of hydrochloric acid.Extract the acidified solution with an equivalent volume of chloroform.Filter the chloroform layer through a pledget of cotton,and concentrate it to a volume of less than 1mL.Combine the resulting solution with 150to 180mg of potassium bromide.Dry the potassium bromide mixture in vacuum overnight,and prepare a pellet from the dried mixture.

Mobile phase and Citrate buffer— Prepare as directed in the Assayunder Carboprost Tromethamine.

Internal standard preparation— Using the Mobile phase,prepare a solution containing about 3mg of guaifenesin per mL.

Standard preparation— Using an accurately weighed quantity of USP Carboprost Tromethamine RS,prepare a Standard solution containing about 0.332mg of USP Carboprost Tromethamine RSper mLand 9mg of benzyl alcohol per mL.Transfer 2.0mLof the solution so obtained into a stoppered centrifuge tube.Add 20.0mLof methylene chloride and 1.0mLof Citrate buffer,shake the stoppered tube for about 10minutes,and centrifuge.Remove and discard the top (aqueous)layer,transfer an 8.0-mLaliquot of the lower (methylene chloride)layer to a suitable vial,and evaporate the solution with the aid of a stream of nitrogen.[NOTE—The residue does not evaporate to dryness because of the presence of benzyl alcohol.]Add 100µLof a freshly prepared solution of a-bromo-2¢-acetonaphthone in acetonitrile (1in 50),and swirl to wash down the sides of the vial.Add 50µLof a freshly prepared solution of diisopropylethylamine in acetonitrile (1in 100).Swirl again,and place the vial in a suitable heating device maintained at a temperature of 30to 35for not less than 15minutes.Evaporate the acetonitrile from the vial with the aid of a stream of nitrogen,add 1.0mLof Internal standard preparation,mix,and pass the resulting solution through a fine-porosity filter.Protect the filtered solution from light prior to injection to prevent degradation of the naphthacyl ester of carboprost.

Assay preparation— Pipet an accurately measured volume of Injection,equivalent to about 500µg of carboprost,to a stoppered,50-mLcentrifuge tube.Proceed as directed for Standard preparation,beginning with “Add 20.0mLof methylene chloride”.

Chromatographic system— Proceed as directed in the Assayunder Carboprost Tromethamine.To evaluate the system suitability requirements,use the Standard preparationprepared as directed in the Assayunder Carboprost Tromethamine.

Procedure— Proceed as directed in the Assayunder Carboprost Tromethamine.Calculate the quantity,in µg,of carboprost (C21H36O5)in each mLof Injection taken by the formula: in which 368.51and 489.64are the molecular weights of carboprost and carboprost tromethamine,respectively;Cis the concentration,in µg per mL,of USP Carboprost Tromethamine RSin the Standard solution used to prepare the Standard preparation;and the other terms are as defined therein.