A: Transfer about 50mLof Oral Solution to a 250-mLseparator,add 20mLof water,5mLof 2.5Nsodium hydroxide,and 40mLof solvent hexane,and shake thoroughly.Remove the solvent hexane layer,and filter through anhydrous sodium sulfate into a 150-mLbeaker.Repeat the solvent hexane extraction,using two 40-mLportions and collecting the extracts in the beaker after filtering.Evaporate the combined extracts at 50under nitrogen to dryness,and dissolve the residue in,and dilute with,10mLof chloroform:the solution is dextrorotatory (see Optical Rotation á781ñ).Retain the chloroform solution for Identificationtest B.

B: Evaporate the chloroform solution from Identificationtest Aon a steam bath to dryness,dissolve the residue in 2mLof 2Nsulfuric acid,and add 1mLof a freshly prepared solution of mercuric nitrate (prepared by dissolving 700mg of mercuric nitrate in 4mLof water,adding 100mg of sodium nitrate,mixing,and filtering):no red color is produced immediately,but after heating,a yellow to red color develops in about 15minutes.

Add the following:

FOR ORAL SOLUTION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.USP28

Add the following:

FOR ORAL SOLUTION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.USP28

Mobile phaseandStandard preparation— Prepare as directed in the Assayunder Dextromethorphan Hydrobromide.

Assay preparation— Pipet,using a to-contain pipet,a volume of Oral Solution,equivalent to about 10mg of dextromethorphan hydrobromide,into a 100-mLvolumetric flask,dilute with water to volume,and mix.

Chromatographic system andProcedure (see Chromatography á621ñ)— Proceed as directed in the Assayunder Dextromethorphan Hydrobromide.Calculate the quantity,in mg,of dextromethorphan hydrobromide (C18H25NO·HBr·H2O)in the volume of Oral Solution taken by the formula: in which 370.32and 352.32are the molecular weights of dextromethorphan hydrobromide and anhydrous dextromethorphan hydrobromide,respectively;Cis the concentration,in mg per mL,of USP Dextromethorphan Hydrobromide RS,on the anhydrous basis,in the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.