Standard solution— Dissolve an accurately weighed quantity of USP Xylometazoline Hydrochloride RSin water to obtain a solution having a known concentration of about 1mg per mL,and proceed as directed for Test solution.

Test solution— Transfer 10mLto a suitable separator,add 2mLof sodium carbonate solution (1in 10),and extract with 10mLof chloroform,filtering the extract through anhydrous sodium sulfate.Evaporate the chloroform extract on a steam bath to dryness,and dissolve the residue in 1mLof a mixture of chloroform and methanol (1:1).

Procedure— Apply separately 5-µLportions of the Test solutionand the Standard solutionto a suitable thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture (see Chromatography á621ñ).Allow the spots to dry,and develop the chromatogram in a solvent system consisting of a mixture of chloroform,methanol,and isopropylamine (92:3:3).Remove the plate from the developing chamber,mark the solvent front,and allow the solvent to evaporate.Spray the plate with p-nitrobenzenediazonium tetrafluoroborate solution,prepared by adding 250mg to 5mLof water,mixing,and filtering.Spray the plate with sodium carbonate solution (1in 10):the RFvalue of the principal spot obtained from the Test solutioncorresponds to that obtained from the Standard solution.

Standard preparation— Dissolve an accurately weighed quantity of USP Xylometazoline Hydrochloride RSin water to obtain a solution having a known concentration of about 0.5mg per mL.Transfer 10.0mLof this solution to a 125-mLseparator,and proceed as directed under Assay preparation,beginning with “add 10mLeach of water and dilute hydrochloric acid (1in 6),respectively.”The concentration of USP Xylometazoline Hydrochloride RSin the Standard preparationis about 100µg per mL.

Assay preparation— Transfer an accurately measured volume of Nasal Solution,equivalent to about 5mg of xylometazoline hydrochloride,to a 125-mLseparator,add 10mLeach of water and dilute hydrochloric acid (1in 6),respectively,and extract with three 10-mLportions of methylene chloride.Discard the methylene chloride extracts,add 10mLof sodium hydroxide solution (1in 5)to the separator,and extract with three 15-mLportions of methylene chloride.Filter the combined extracts through glass wool into a 50-mLvolumetric flask,dilute with methylene chloride to volume,and mix.

Procedure— Transfer 5.0mLeach of the Standard preparationand the Assay preparation,respectively,to separate 10-mLvolumetric flasks,and evaporate in a water bath maintained at 40,with the aid of a stream of nitrogen,to dryness.Dissolve the residue in each flask in 0.50mLof dehydrated alcohol,and add 0.50mLof dehydrated alcohol to a third 10-mLvolumetric flask to provide the blank.To each flask add 0.50mLof sodium hydroxide solution (1in 25),swirl,to each add 5.0mLof sodium nitroferricyanide solution (1in 200),and mix.After 10minutes,accurately timed,add 1.0mLof a saturated solution of sodium bicarbonate to each flask,swirl,and allow to stand for 10minutes.Dilute each with water to volume,mix,and allow to stand for 15minutes.Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 565nm,with a suitable spectrophotometer,using the blank to set the instrument.Calculate the quantity,in mg,of xylometazoline hydrochloride (C16H24N2·HCl)in each mLof the Nasal Solution taken by the formula: in which Cis the concentration,in µg per mL,of USP Xylometazoline Hydrochloride RSin the Standard preparation,Vis the volume,in mL,of Nasal Solution taken,and AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively.