A: To an amount of the Oral Solution equivalent to about 100mg of dyphylline,add water to make 20mL,mix,and add 2.0mLof 2Nsodium hydroxide and 2drops of potassium permanganate TS:a green color is produced.

B: Transfer a volume of Oral Solution,equivalent to about 100mg of guaifenesin,to a 60-mLseparator,add 10mLof chloroform,shake for 30seconds,and allow the layers to separate.Decant the lower (chloroform)layer through chloroform-washed cotton into a small beaker.Evaporate 1mLof the extract,on a watch glass,on a steam bath to dryness.To the residue add 1drop of formaldehyde TSand a few drops of sulfuric acid:a deep cherry-red to purple color is produced.

C: The retention times of the major peaks in the chromatogram of the Assay preparationcorrespond to those in the chromatogram of the Standard preparation,as obtained in the Assay.

Standard preparation,Test preparation,Chromatographic system,and Procedure— Proceed as directed in Alcohol contentunder Dyphylline Oral Solution:the alcohol content is between 90.0%and 110.0%of the labeled amount of C2H5OH.

Mobile phase— Prepare a suitable filtered and degassed mixture of 0.01Mmonobasic potassium phosphate and methanol (79:21).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve accurately weighed quantities of USP Dyphylline RSand USP Guaifenesin RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having known concentrations of about 0.1mg of guaifenesin and about 0.1Jmg of dyphylline per mL,Jbeing the ratio of the labeled amount of dyphylline to that of guaifenesin.

Resolution solution— Prepare a solution in Mobile phasecontaining in each mLabout 0.1mg each of dyphylline and guaifenesin and about 0.01mg of guaiacol.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 100mg of guaifenesin,to a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 230-nm detector,a guard column that contains packing L1,and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution,R,between the guaiacol and guaifenesin peaks is not less than 1.8,and the resolution,R,between the guaiacol and dyphylline peaks is not less than 9.0.The relative retention times are about 0.25for dyphylline,0.7for guaiacol,and 1.0for guaifenesin.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%for both dyphylline and guaifenesin.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantities,in mg,of dyphylline (C10H14N4O4)and guaifenesin (C10H14O4)in each mLof the Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of the appropriate USP Reference Standard in the Standard preparation,Vis the volume,in mL,of Oral Solution taken;and rUand rSare the peak responses of the corresponding analyte obtained from the Assay preparationand the Standard preparation,respectively.