Sodium Fluoride and Phosphoric Acid Gel
» Sodium Fluoride and Phosphoric Acid Gel contains not less than 90.0 percent and not more than 110.0 percent 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.
A: Place a quantity of Gel, equivalent to about 500 mg of fluoride ion, in a platinum crucible in a well-ventilated hood, and add 15 mL of sulfuric acid. Cover the crucible with a piece of clear, polished glass, and heat on a steam bath for 1 hour. 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 191.
Viscosity 911 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 ± 0.5 until it adjusts to the temperature of the water bath (30 minutes or longer). Do not stir the gel while it is in the bath. Remove the sample from the bath, stir the gel gently for 5 seconds, 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 60 rpm or of 30 rpm. Calculate the viscosity, in centipoises, by multiplying the scale reading by the constant for the spindle and speed used: the viscosity is between 7000 and 20,000 centipoises.
pH 791 Place about 40 mL in a plastic beaker, and determine the pH using a suitable electrode system: the pH is between 3.0 and 4.0.
Assay— [note—Store all solutions, except Buffer solution, in plastic containers.]
Buffer solution and Standard preparations— Prepare as directed in the Assay under Sodium Fluoride Oral Solution.
Assay preparation— Transfer a quantity of Gel, equivalent to about 20 mg of fluoride ion, accurately weighed, to a 1000-mL volumetric flask, add water to dissolve, dilute with water to volume, and mix.
Procedure— Proceed as directed for Procedure in the Assay under 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— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Senior Scientist
(MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 3576
Pharmacopeial Forum: Volume No. 33(3) Page 455