Sodium Fluoride and Phosphoric Acid Gel
»Sodium Fluoride and Phosphoric Acid Gel contains not less than 90.0percent and not more than 110.0percent of the labeled amount of fluoride ion,in an aqueous medium containing a suitable viscosity-inducing agent.
Packaging and storage— Preserve in tight,plastic containers.
Labeling— Label Gel in terms of the content of sodium fluoride (NaF)and in terms of the content of fluoride ion.
Identification—
A: Place a quantity of Gel,equivalent to about 500mg of fluoride ion,in a platinum crucible in a well-ventilated hood,and add 15mLof sulfuric acid.Cover the crucible with a piece of clear,polished glass,and heat on a steam bath for 1hour.Remove the glass cover,rinse it in water,and dry:the glass surface exposed to vapors from the crucible is etched.
B: It responds to the tests for Phosphate á191ñ.
Viscosity á911ñ— Place a quantity of Gel in a suitable plastic container,insert the stopper securely,and allow to stand until the gel is free from air bubbles.Place it in a water bath maintained at a temperature of 25±0.5until it adjusts to the temperature of the water bath (30minutes or longer).Do not stir the gel while it is in the bath.Remove the sample from the bath,stir the gel gently for 5seconds,and without delay,using a rotational viscosimeter,determine the viscosity using the appropriate spindle to obtain a scale reading between 10%and 90%of full scale at a speed of 60rpm or of 30rpm.Calculate the viscosity,in centipoises,by multiplying the scale reading by the constant for the spindle and speed used:the viscosity is between 7000and 20,000centipoises.
pHá791ñ— Place about 40mLin a plastic beaker,add about 250mg of quinhydrone,and stir for 1minute,leaving some of the quinhydrone undissolved.Determine the pHusing a hydrofluoric acid frit-junction calomel reference electrode and a platinum electrode:the pHis between 3.0and 4.0.
Assay— [NOTE—Store all solutions,except Buffer solution,in plastic containers.]
Buffer solution andStandard preparations— Prepare as directed in the Assayunder Sodium Fluoride Oral Solution.
Assay preparation— Transfer a quantity of Gel,equivalent to about 20mg of fluoride ion,accurately weighed,to a 1000-mLvolumetric flask,add water to dissolve,dilute with water to volume,and mix.
Procedure— Proceed as directed for Procedurein the Assayunder Sodium Fluoride Oral Solution.The quantity,in mg,of fluoride ion in the portion of Gel taken is equivalent to C,the determined concentration of fluoride ion,in µg per mL,in the Assay preparation.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1785
Phone Number:1-301-816-8251