Sodium Fluoride and Acidulated Phosphate Topical Solution
» Sodium Fluoride and Acidulated Phosphate Topical Solution contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of fluoride ion.
Packaging and storage Preserve in tight plastic containers.
Labeling Label Topical Solution in terms of the content of sodium fluoride (NaF) and in terms of the content of fluoride ion. The labeling indicates the Assay test with which the article complies if a test other than Test 1 is used.
USP Reference standards 11
USP Sodium Fluoride RS
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 4.5.
Other requirements It responds to the Identification tests under Sodium Fluoride and Phosphoric Acid Gel.
Buffer solution and Standard preparations Prepare as directed in the Assay under Sodium Fluoride Oral Solution.
Assay preparation Transfer an accurately measured volume of Topical Solution, equivalent to about 20 mg of fluoride ion, 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. Calculate the quantity, in mg, of fluoride ion in each mL of the Topical Solution taken by the formula:
C / Vin which C is the determined concentration of fluoride ion, in µg per mL, in the Assay preparation, and V is the volume, in mL, of Topical Solution taken.
test 2 [noteUse Purified Water (resistivity not less than 18 megohm-cm) for the Mobile phase and all preparations. ]
Mobile phase Dissolve about 300 mg of anhydrous sodium carbonate in 2000 mL of water, add 2.0 mL of 1 N sodium hydroxide, mix, and pass through a 0.45-µm nylon filter.
Standard stock preparation Dissolve a suitable quantity of USP Sodium Fluoride RS in water to obtain a solution having a known concentration of about 0.11 mg per mL.
Standard preparation Transfer 5.0 mL of the Standard stock solution to a 500-mL volumetric flask, dilute with water to volume, and pass through a 0.45-µm nylon or PTFE filter. This solution contains about 1.1 µg of sodium fluoride per mL.
Assay preparation Transfer 10.0 mL of the Topical Solution to a suitable volumetric flask, dilute with water quantitatively, and stepwise if necessary, to obtain a solution having a known concentration of about 1.1 µg of sodium fluoride per mL, based on the label claim, and pass through a 0.45-µm nylon or PTFE filter.
Chromatographic system (see Chromatography 621) The liquid chromatograph is equipped with a conductivity detector with a suitable suppression unit and a 4.6-mm × 25-cm column and a 4.6-mm × 50-mm guard column, both containing packing L46 (see Chromatographic Reagents under Reagents, Indicators, and Solutions). The flow rate is about 1.0 mL per minute. [noteIt is recommended to use polymethylpentene HPLC vials. ] Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the elution order is fluoride, followed by the chloride peak; the resolution, R, between fluoride and chloride is not less than 1.5; the column efficiency is not less than 1500 theoretical plates; the tailing factor for the fluoride peak is not more than 2.0; and the relative standard deviation for six replicate injections is not more than 2.0% for the fluoride peak. [noteChloride is an impurity that is present in USP Sodium Fluoride RS. ]
Procedure Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the fluoride peaks. Calculate the percentage, P (w/v), of sodium fluoride in the portion of Topical Solution taken by the formula:
100×0.001×CS (D / V)(rU / rS)in which 0.001 is the conversion factor from mg to g; CS is the concentration, in mg per mL, of sodium fluoride in the Standard preparation;D is the dilution factor for the Assay preparation; V is the volume, in mL, of Topical Solution taken to prepare the Assay preparation; and rU and rS are the fluoride peak responses obtained from the Assay preparation and the Standard preparation, respectively.
Calculate the percentage (w/v) of fluoride ion in the portion of Topical Solution taken by the formula
P×19.00 / 41.99
in which P is as defined above; 19.00 is the atomic weight of fluorine; and 41.99 is the molecular weight of sodium fluoride.
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USP35NF30 Page 4660Pharmacopeial Forum: Volume No. 33(3) Page 454