Topical Starch »Topical Starch consists of the granules separated from the mature grain of corn [Zea maysLinné(Fam.Gramineae)]. Packaging and storage— Preserve in well-closed containers. Botanic characteristics— Polygonal,rounded or spheroidal granules up to about 35µm in diameter and usually having a circular or several-rayed central cleft. Identification— A: Prepare a smooth mixture of 1g of it with 2mLof cold water,stir it into 15mLof boiling water,boil gently for 2minutes,and cool:a translucent,whitish jelly is produced. B: Awater slurry of it is colored reddish violet to deep blue by iodine TS. Microbial limits á61ñ The total aerobic microbial count does not exceed 500cfu per g and the total combined molds and yeasts count does not exceed 50cfu per g. pHá791ñ Prepare a slurry by weighing 20.0g ±100mg of Topical Starch,transferring to a suitable nonmetallic container,and adding 100mLof water.Agitate continuously at a moderate rate for 5minutes,then stop agitation,and immediately determine the pHto the nearest 0.1unit:the pH,determined potentiometrically,is between 4.5and 7.0. Loss on drying á731ñ Dry it at 120for 4hours:it loses not more than 14.0%of its weight. Residue on ignition á281ñ: not more than 0.5%,determined on a 2.0-g test specimen ignited at a temperature of 575±25. Iron á241ñ Dissolve the residue obtained in the test for Residue on ignitionin 4mLof hydrochloric acid with the aid of gentle heating,dilute with water to 50mL,and mix.Dilute 25mLof the resulting solution with water to 47mL:the limit is 0.001%. Oxidizing substances— Transfer 4.0g to a glass-stoppered,125-mLconical flask,and add 50.0mLof water.Insert the stopper,and swirl for 5minutes.Decant into a glass-stoppered,50-mLcentrifuge tube,and spin to clarify.Transfer 30.0mLof clear supernatant to a glass-stoppered,125-mLconical flask.Add 1mLof glacial acetic acid and 0.5g to 1.0g of potassium iodide.Insert the stopper,swirl,and allow to stand for 25to 30minutes in the dark.Add 1mLof starch TS,and titrate with 0.002Nsodium thiosulfate VSto the disappearance of the starch-iodine color.Each mLof 0.002Nsodium thiosulfate is equivalent to 34µg of oxidant,calculated as hydrogen peroxide.Not more than 12.6mLof 0.002Nsodium thiosulfate is required (0.018%). Sulfur dioxide— Mix 20g with 200mLof water to obtain a smooth suspension,and filter.To 100mLof the clear filtrate add 3mLof starch TS,and titrate with 0.01Niodine VSto the first permanent blue color:not more than 2.7mLis consumed (0.008%). Auxiliary Information— Staff Liaison:Catherine Sheehan,B.Sc.,Scientist Expert Committee:(EMC)Excipients:Monograph Content USP28–NF23Page 1804 Pharmacopeial Forum:Volume No.29(3)Page 669 Phone Number:1-301-816-8262