Lime
CaO 56.08

Calcium oxide [1305-78-8].
»Lime,when freshly ignited to constant weight,contains not less than 95.0percent of CaO.
Packaging and storage— Preserve in tight containers.
Identification—
A: Moisten it with water:heat is generated,and a white powder is obtained (calcium hydroxide or slaked lime).Mix the powder with 3or 4times its weight of water:a smooth magma of lime forms that is alkaline to litmus.
B: Slake 1g with 20mLof water,and add 6Nacetic acid until the lime is dissolved:the resulting solution responds to the test for Calcium á191ñ.
Loss on ignition á733ñ— Ignite a portion to constant weight in a tared platinum crucible at 1100±50:it loses not more than 10.0%of its weight.
Insoluble substances— Slake 5.0g,then mix with 100mLof water,followed by hydrochloric acid,dropwise,with agitation,until solution takes place:the resulting solution after boiling and cooling is acid,and when filtered through a tared crucible,washed with water until free of chlorides,and dried at 105for 1hour yields not more than 50mg of insoluble substances (1.0%).
Carbonate— Slake 1g,mix with 50mLof water,and decant the greater portion of the milky liquid:the addition of an excess of 3Nhydrochloric acid to the residue does not cause more than a slight effervescence.
Magnesium and alkali salts— Dissolve 500mg in 30mLof water and 15mLof 3Nhydrochloric acid.Neutralize the solution with 6Nammonium hydroxide,heat to boiling,and add ammonium oxalate TSto precipitate the calcium completely.Heat the mixture on a steam bath for 1hour,cool,dilute with water to 100mL,mix,and filter.To 50mLof the filtrate add 0.5mLof sulfuric acid,evaporate to dryness,and ignite in a tared platinum crucible to constant weight.The weight of the residue does not exceed 9mg.
Organic volatile impurities,Method IVá467ñ: meets the requirements.
Assay— Ignite about 1g of Lime in a muffle furnace to constant weight,cool,weigh accurately,and dissolve in 20mLof 3Nhydrochloric acid.Cool the solution,transfer to a 500-mLvolumetric flask with the aid of water,dilute with water to volume,and mix.Transfer 50.0mLto a suitable container,add 100mLof water,15mLof 1Nsodium hydroxide,and 300mg of hydroxy naphthol blue,and titrate with 0.05Medetate disodium VSuntil the solution is deep blue in color.Each mLof 0.05Medetate disodium is equivalent to 2.804mg of CaO.
Auxiliary Information— Staff Liaison:Behnam Davani,Ph.D.,MBA,Senior Scientist
Expert Committee:(PA7)Pharmaceutical Analysis 7
USP28–NF23Page 1133
Phone Number:1-301-816-8394