C7H8O 108.14

3-Methylphenol.
3-Hydroxytoluene [108-39-4].

Packaging and storage— Preserve in tight,light-resistant containers.

Clarity of solution—

Identification— Shake 10mLof it with 30mLof water in a separator,and allow to separate.The lower layer is clear;the upper layer clears slowly.To 5mLof the upper layer add a drop of ferric chloride TS:a bluish color is produced.To a separate 5-mLportion of the upper layer add bromine TSdropwise:a white precipitate is obtained.

Assay— Transfer about 10drops of Metacresol to an accurately tared 100-mLvolumetric flask,and weigh to determine the amount,in mg,added.Add about 50mLof 1Nsodium hydroxide,shake to dissolve,dilute with 1Nsodium hydroxide to volume,and mix.Transfer 10.0mLof this solution to an iodine flask,add about 50mLof water and sufficient 18Nsulfuric acid to neutralize the solution to litmus,and cool to 20.Add 25.0mLof 0.1Nbromine VSand 15mLof hydrochloric acid,and immediately insert the stopper.Shake the flask,and cool under running water.Allow to stand in a cool,dark place for 30minutes,shaking every 10minutes.Cool to 20,quickly add 5mLof potassium iodide solution (1in 5)to the collar of the flask,gently lift the stopper momentarily,and allow the solution to be drawn into the flask,shake thoroughly,remove the stopper,and rinse it and the inside neck of the flask with a small quantity of water so that the washing flows into the flask.Add 1mLof chloroform,shake,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 1.802mg of C7H8O.

Expert Committee:(PA6)Pharmaceutical Analysis 6

USP28–NF23Page 1226

Phone Number:1-301-816-8389