A:Infrared Absorption á197Kñ—

B: The retention time of the major peak in the chromatogram of the Test solutioncorresponds to that of emedastine in the chromatogram of the System suitability solution,as obtained from the Chromatographic puritytest.

C: Dissolve about 23mg of Emedastine Difumarate in 25mLof water.Add 1mLof a solution prepared by mixing 20mLof cupric sulfate solution (1in 5)and 8mLof pyridine:a precipitate is formed in the blue solution within one minute.

Buffer solution— Dissolve 3.9g of monobasic sodium phosphate and 2.5g of sodium dodecyl sulfate in 1.0liter of water.Adjust with phosphoric acid to a pHof 2.4.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solutionand acetonitrile (1:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability solution— Prepare a solution in Mobile phasecontaining 0.10mg of USP Emedastine Difumarate RSand 0.04mg of 4-methylbenzophenone per mL.

Standard solution— Dissolve an accurately weighed quantity of USP Emedastine Difumarate RSin Mobile phase,and dilute,stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.003mg per mL.

Test solution— Prepare a solution of Emedastine Difumarate in Mobile phasecontaining about 1.0mg per mL.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L1.The flow rate is about 1.0mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.2for fumaric acid,1.0for emedastine,and 2.0for 4-methylbenzophenone;the resolution,R,is not less than 2.0;the column efficiency determined from the emedastine peak is not less than 1500theoretical plates;the tailing factor is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Mobile phase,Standard solution,and Test solutioninto the chromatograph,and record the chromatograms,allowing the elution to continue for a period of not less than twice the retention time of emedastine.Measure the areas for all of the peaks,disregarding the fumaric acid peak and peaks corresponding to those obtained from the Mobile phase.Calculate the percentage of each impurity in the portion of Emedastine Difumarate taken by the formula: in which riis the peak response for each impurity obtained from the Test solution;and rSis the peak response for emedastine in the Standard solution:not more than 0.3%of any individual impurity is found;and not more than 1.0%of total impurities is found.