Packaging and storage— Preserve in well-closed containers,preferably at controlled room temperature.

Assay— Weigh accurately an amount of Plaster,corresponding to about 500mg of salicylic acid,cut the portion into small strips,place them in a small flask,add 50mLof chloroform,and shake the mixture until the plaster mass is disintegrated.Decant the chloroform extract into a 250-mLbeaker,and wash the plaster backing with two 25-mLportions of chloroform,receiving the washings in the same beaker.Then wash the backing with 50mLof alcohol to which has been added 1mLof 6Nammonium hydroxide,and add the washing to the chloroform extract.Again wash the backing with 40mLof alcohol,and add the washing to the chloroform extract.Dry the backing,weigh,and subtract the weight from the weight of Plaster taken for the assay to obtain the weight of plaster mass.Stir the chloroform extract until any coagulum has separated into a compact mass,and filter the extract through purified cotton into a separator.Knead the coagulum,if any,with a glass rod to expel the solvent,and rinse the coagulum and the beaker with 10mLof alcohol.Pour the rinsing through the cotton,then press the cotton with a glass rod to expel the solvent.Extract the filtrate with three 10-mLportions of 1Nsodium hydroxide,drawing off each portion into a 500-mLvolumetric flask,and finally wash with two 25-mLportions of water,receiving the washings in the same flask.Dilute with water to volume,and pipet a 25-mLaliquot into a 500-mLiodine flask.Add 30.0mLof 0.1Nbromine VS,then add 5mLof hydrochloric acid,and immediately insert the stopper.Shake the flask repeatedly during 30minutes,allow it to stand for 15minutes,add quickly 5mLof potassium iodide solution (1in 5),taking precautions against the escape of bromine vapor,and at once insert the stopper in the flask.Shake thoroughly,remove the stopper,and rinse it and the neck of the flask with a small quantity of water,so that the washing flows into the flask.Add 1mLof chloroform,shake the mixture,and titrate the liberated iodine with 0.1Nsodium thiosulfate VS,adding 3mLof starch TSas the endpoint is approached.Perform a blank determination (see Residual Titrationsunder Titrimetry á541ñ).Each mLof 0.1Nbromine is equivalent to 2.302mg of C7H6O3.

Expert Committee:(PA6)Pharmaceutical Analysis 6

USP28–NF23Page 1748

Phone Number:1-301-816-8389