Calamine

Iron oxide (Fe2O3),mixture with zinc oxide.
Calamine (pharmaceutical preparation) [8011-96-9].
»Calamine is Zinc Oxide with a small proportion of ferric oxide,and contains,after ignition,not less than 98.0percent and not more than 100.5percent of zinc oxide (ZnO).
Packaging and storage— Preserve in well-closed containers.
Identification—
A: Treat 1g with 10mLof 3Nhydrochloric acid,and filter:the filtrate responds to the tests for Zinc á191ñ.
B: Treat 1g with 10mLof 3Nhydrochloric acid,heat to boiling,and filter:the filtrate assumes a reddish color upon the addition of ammonium thiocyanate TS.
Microbial limits á61ñ— It meets the requirements of the tests for absence of Staphylococcus aureusand Pseudomonas aeruginosa.
Loss on ignition á733ñ— Weigh accurately about 2g,and ignite at 500to constant weight:it loses not more than 2.0%of its weight.
Acid-insoluble substances— Dissolve 2.0g in 50mLof 3Nhydrochloric acid.If an insoluble residue remains,collect it on a tared filter,wash with water,dry at 105for 1hour,cool,and weigh:the weight of the residue does not exceed 40mg (2.0%).
Alkaline substances— Digest 1.0g with 20mLof water on a steam bath for 15minutes,filter,and add 2drops of phenolphthalein TS:if a red color is produced,not more than 0.20mLof 0.10Nsulfuric acid is required to discharge it.
Calcium— Digest 1g in 25mLof 3Nhydrochloric acid for 30minutes,filter to remove the insoluble ferric oxide,and add 6Nammonium hydroxide to the filtrate until the precipitate first formed is redissolved,then add 5mLmore of 6Nammonium hydroxide.To 10mLof this solution add 2mLof ammonium oxalate TS:not more than a slight turbidity is produced.
Calcium or magnesium— To another 10-mLportion of the solution prepared for the test for Calciumadd 2mLof dibasic sodium phosphate TS:not more than a slight turbidity is produced.
Lead— To 1g add 15mLof water,stir,then add 3mLof glacial acetic acid,and warm on a steam bath until dissolved.Filter,and add 5drops of potassium chromate TS:no turbidity is produced.
Assay— Digest about 1.5g of freshly ignited Calamine,accurately weighed,with 50.0mLof 1Nsulfuric acid VS,applying gentle heat until no further solution occurs.Filter the mixture,and wash the residue on the filter with hot water until the last washing is neutral to litmus paper.To the combined filtrate and washings add 2.5g of ammonium chloride,cool,add methyl orange TS,and titrate with 1Nsodium hydroxide VS.Each mLof 1Nsulfuric acid is equivalent to 40.69mg of ZnO.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(PA6)Pharmaceutical Analysis 6
USP28–NF23Page 314
Phone Number:1-301-816-8389