Calcium Silicate
»Calcium Silicate is a compound of calcium oxide and silicon dioxide.It contains not less than 4.0percent of calcium oxide and not less than 45.0percent of silicon dioxide.
Packaging and storage— Preserve in well-closed containers.
Labeling— The labeling states the claimed percentage or range of percentages for the content of calcium oxide and for the content of silicon dioxide.
Identification—
A: Mix 0.5g with 10mLof 3Nhydrochloric acid,filter,and neutralize the filtrate to litmus paper with 6Nammonium hydroxide:the neutralized filtrate so obtained responds to the tests forCalcium á191ñ.
B: Prepare a bead by fusing a few crystals of sodium ammonium phosphate on a platinum loop in the flame of a gas burner.Place the hot,transparent bead in contact with the specimen of Calcium Silicate,and again fuse.Silica floats about in the bead,producing,upon cooling,an opaque bead having a web-like structure.
pHá791ñ: between 8.4and 10.2,determined in a well-mixed aqueous suspension (1in 20).
Loss on ignition á733ñ— Transfer about 1g,accurately weighed,to a suitable tared crucible,dry at 105for 2hours,and ignite at 900to constant weight:it loses not more than 20.0%of its weight.
Lead á251ñ— Dissolve 1.0g in 20mLof 3Nhydrochloric acid,evaporate on a steam bath to about 10mL,dilute with water to about 20mL,and cool:the limit is 0.001%.
Heavy metals á231ñ— Boil 4.0g with a mixture of 50mLof water and 10mLof hydrochloric acid for 20minutes,adding water to maintain the volume during the boiling.Add ammonium hydroxide until the mixture is only slightly acid to litmus paper.Filter with the aid of suction,and wash with 15mLto 20mLof water,combining the washing with the original filtrate.Add 2drops of phenolphthalein TS,then add a slight excess of 6Nammonium hydroxide.Discharge the pink color with dilute hydrochloric acid (1in 100).Dilute with water to 100mL,and use 25mLof the solution for the test:the limit is 20µg per g.
Limit of fluoride—
NOTE—Store all solutions in plastic containers.
Buffer solution— Add 800mLof hot water to 74.4g of edetate disodium and 24.2g of tris(hydroxymethyl)aminomethane,and stir until dissolved.Adjust with 5Nsodium hydroxide to a pHof 7.5to 7.6.Allow the solution to cool,and adjust with 5Nsodium hydroxide to a pHof 8.0.Dilute with water to 1000mL,and mix.
Electrode system— Use a fluoride-specific,ion-indicating electrode and a calomel reference electrode connected to a pHmeter capable of measuring potentials with a reproducibility of ±0.2mV(seepHá791ñ).
Standard stock solution— Dissolve an accurately weighed quantity of USP Sodium Fluoride RSquantitatively in water to obtain a solution containing 221µg per mL.Each mLof this stock solution contains 100µg of fluoride ion.
Standard solutions [NOTE—Prepare on the day of use.]—Transfer 10.0mLofStandard stock solutionto a 100-mLvolumetric flask,dilute with water to volume,and mix.This solution contains 10µg of fluoride ion per mL(Standard solution A).Transfer 1.0mLofStandard stock solutionto a second 100-mLvolumetric flask,dilute with water to volume,and mix.This solution contains 1.0µg of fluoride ion per mL(Standard solution B).
Test solution— Transfer 5.0g of Calcium Silicate to a 150-mLpolytef beaker.Add 40mLof water and 20mLof 1Nhydrochloric acid.Heat to near boiling for 1minute,stirring continuously.Cool in an ice bath,transfer the suspension to a 100-mLvolumetric flask,dilute with water to volume,and mix.
Procedure— Transfer 20.0mLofStandard solution A,Standard solution B,and theTest solutionto separate polytef beakers,add 10.0mLofBuffer solutionto each beaker,and stir with a plastic-coated stirring bar.Concomitantly measure the potentials,in mV,of the solutions.[NOTE—When taking measurements,immerse the electrodes in the solution,stir on a magnetic stirrer having an insulated top until equilibrium is attained (1to 2minutes),and record the potential.Rinse and dry the electrodes between measurements,taking care to avoid damaging the crystal of the ion-specific electrode.]Plot the logarithms of the fluoride ion concentrations,in µg per mL,of theStandard solutionsversus potential,in mV.From the measured potential of theTest solutionand the standard response line,determine the concentration,C,in µg per mL,of fluoride ion in theTest solution.Calculate the quantity,in µg of fluoride per g of Calcium Silicate by multiplyingCby 20.The limit is 10µg per g.
Assay for silicon dioxide— Transfer about 400mg of Calcium Silicate,accurately weighed,to a beaker,add 5mLof water and 10mLof perchloric acid,and heat until dense white fumes of perchloric acid are evolved.Cover the beaker with a watch glass,and continue to heat for 15minutes longer.Allow to cool,add 30mLof water,filter,and wash the precipitate with 200mLof hot water.[NOTE—Retain the combined filtrate and washings for use in theAssay for calcium oxide.]Transfer the filter paper and its contents to a platinum crucible,heat slowly to dryness,then heat sufficiently to char the filter paper.After cooling,add a few drops of sulfuric acid,and ignite at about 1300to constant weight.Moisten the residue with 5drops of sulfuric acid,add 15mLof hydrofluoric acid,heat cautiously on a hot plate until all of the acid is driven off,and ignite at a temperature not lower than 1000to constant weight.Cool in a desiccator,and weigh:the loss in weight represents the weight of SiO2.The percentage of silicon dioxide in the Calcium Silicate is between 90.0%and 110.0%of the content stated in the labeling,or within the range of percentages stated in the labeling.
Assay for calcium oxide— Neutralize the combined filtrate and washings retained from theAssay for silicon dioxideto litmus with 1Nsodium hydroxide.Add,while stirring,about 30mLof 0.05Medetate disodium VSfrom a 50-mLburet.Add 15mLof 1Nsodium hydroxide and 300mg of hydroxy naphthol blue,and continue the titration to a blue endpoint.Each mLof 0.05Medetate disodium is equivalent to 2.804mg of CaO.The percentage of CaOin the Calcium Silicate is between 90.0%and 110.0%of the content stated in the labeling,or within the range of percentages stated in the labeling.
Ratio of SiO2to CaO— Divide the percentage of SiO2obtained in theAssay for silicon dioxideby the percentage of CaOobtained in theAssay for calcium oxide:the quotient obtained is between 1.3and 20.
Sum of CaO,SiO2,and Loss on ignition— The sum of the percentages obtained in the three tests is not less than 90.0%.
Auxiliary Information— Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 2970
Pharmacopeial Forum:Volume No.30(2)Page 595
Phone Number:1-301-816-8262