Zinc Stearate
Octadecanoic acid,zinc salt.
Zinc stearate [557-05-1]. »Zinc Stearate is a compound of zinc with a mixture of solid organic acids obtained from fats,and consists chiefly of variable proportions of zinc stearate and zinc palmitate.It contains the equivalent of not less than 12.5percent and not more than 14.0percent of ZnO. Packaging and storage— Preserve in well-closed containers. Identification— A: Mix 25g with 200mLof hot water,add 60mLof 2Nsulfuric acid,and boil until the fatty acids separate as a transparent layer.Cool the mixture,and remove the solidified layer of fatty acids:a portion of the water layer responds to the tests for Zinc á191ñ. B: Place the separated fatty acids obtained in Identificationtest Ain a filter wetted with water,and wash with boiling water until free from sulfate.Collect the fatty acids in a small beaker,allow to cool,pour off the separated water,then melt the acids,filter into a dry beaker while hot,and dry at 105for 20minutes:the fatty acids congeal (see Congealing Temperature á651ñ)at a temperature not below 54. Arsenic,Method Iá211ñ Prepare the Test Preparationas follows.Mix 5.0g with 50mLof water,cautiously add 5mLof sulfuric acid,and boil gently until the fatty acids layer is clear and the volume is reduced to about 25mL.Filter while hot,cool the filtrate,and dilute with water to 50mL.Transfer a 20-mLaliquot to the arsine generator flask,and dilute with water to 35mL.The limit is 1.5ppm. Lead— Ignite 0.50g in a platinum crucible for 15to 20minutes in a muffle furnace at 475to 500.Cool,add 3drops of nitric acid,evaporate over a low flame to dryness,and ignite again at 475to 500for 30minutes.Dissolve the residue in 1mLof 8Nnitric acid,and proceed as directed in the test for Leadunder Magnesium Stearate.The limit is 0.001%. Alkalies and alkaline earths— Mix 2.0g with 50mLof water,add 10mLof hydrochloric acid,boil until the solution is clear,filter while hot,and wash the separated fatty acids with about 50mLof hot water.Render the combined filtrate and washings alkaline with 6Nammonium hydroxide,add ammonium sulfide TSto precipitate the zinc completely,dilute with water to 200mL,mix,and filter.To 100mLof the clear filtrate add 0.5mLof sulfuric acid,evaporate to dryness,and ignite to constant weight:the weight of the residue does not exceed 10mg (1.0%). Organic volatile impurities,Method IVá467ñ: meets the requirements. Assay— Boil about 1g of Zinc Stearate,accurately weighed,with 50mLof 0.1Nsulfuric acid for at least 10minutes,or until the fatty acids layer is clear,adding more water as necessary to maintain the original volume,cool,and filter.Wash the filter and the flask thoroughly with water until the last washing is not acid to litmus paper.Add to the combined filtrate and washings 15mLof ammonia–ammonium chloride buffer TSand 0.2mLof eriochrome black TS,heat the solution to about 40,and titrate with 0.05Medetate disodium VSuntil the solution is deep blue in color.Each mLof 0.05Medetate disodium is equivalent to 4.069mg of ZnO. Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist Expert Committee:(PA6)Pharmaceutical Analysis 6 USP28–NF23Page 2055 Phone Number:1-301-816-8389