DEFINITION
Content: 98.5 per cent to 100.5 per cent (dried substance).
CHARACTERS
Appearance: White or almost white powder or colourless crystals.
Solubility: Soluble in water, practically insoluble in ethanol (96 per cent).
IDENTIFICATION
A. To 2 ml of solution S (see Tests) add 0.5 ml of calcium chloride solution R. A gelatinous white precipitate is formed that dissolves on adding 5 ml of ferric chloride solution R1.
B. To about 4 mg add a mixture of 0.1 ml of alizarin S solution R and 0.1 ml of zirconyl nitrate solution R and mix. The colour changes from red to yellow.
C. Solution S gives reaction (a) of sodium.
TESTS
Solution S: Dissolve 2.5 g in carbon dioxide-free water R without heating and dilute to 100 ml with the same solvent.
Appearance of solution: Solution S is clear (2.2.1) and colourless.
Acidity or alkalinity: Dissolve 2.5 g of potassium nitrate R in 40 ml of solution S and dilute to 50 ml with carbon dioxide-free water R. Cool to 0 °C and add 0.2 ml of phph solution R. If the solution is colourless, not more than 1.0 ml of 0.1 M sodium hydroxide is required to produce a red colour that persists for at least 15 s. If the solution is red, not more than 0.25 ml of 0.1 M hydrochloric acid is required to change the colour of the indicator.
Chlorides: Maximum 200 ppm.
Fluorosilicates: Heat to boiling the neutralised solution obtained in the test for acidity or alkalinity and titrate whilst hot. Not more than 0.75 ml of 0.1 M sodium hydroxide is required to change the colour of the indicator to red.
Sulphates: Maximum 200 ppm.
Loss on drying: Maximum 0.5 per cent, determined on 1.000 g by drying in an oven at 130°C for 3 h.
ASSAY
Dissolve 0.100 g in water R and dilute to 60 ml with the same solvent. Titrate with 0.1 M La-nitrate ( La(NO3)3), determining the end-point potentiometrically (2.2.20) using a fluorideselective
indicator electrode and a silver-silver chloride reference electrode.
1 ml of 0.1 M La-nitrate ( La(NO3)3) is equivalent to 12.60 mg of NaF.
NaF 41.99 -- [7681-49-4].
Sodium Fluoride contains not less than 98.0 percent and not more than 102.0 percent of NaF, calculated on the dried basis.
Identification:
A: Place 1 g in a platinum crucible in a well-ventilated hood, add 15 mL of sulfuric acid, and cover the crucible with a piece of clear, polished glass. Heat the crucible on a steam bath for 1 hour, remove the glass cover, rinse it in water, and wipe dry: the surface of the glass is etched.
B: A solution (1 in 25) responds to the tests for Sodium.
Tests:
Acidity or alkalinity: Dissolve 2.0 g in 40 mL of water in a platinum dish, add 10 mL of a saturated solution of potassium nitrate, cool the solution to 0 , and add 3 drops of phph. If no color appears, a pink color persisting for 15 seconds is produced by not more than 2.0 mL of 0.10 N sodium hydroxide. If the solution is colored pink by the addition of phph, it is rendered colorless by not more than 0.50 mL of 0.10 N sulfuric acid. Save the neutralized solution for the test for Fluosilicate.
Loss on drying: Dry it at 150 for 4 hours: it loses not more than 1.0% of its weight.
Fluosilicate: After the solution from the test for Acidity or alkalinity has been neutralized, heat to boiling, and titrate while hot with 0.10 N sodium hydroxide until a permanent pink color is obtained: not more than 1.5 mL of 0.10 N sodium hydroxide is required.
Chloride: Dissolve 300 mg in 20 mL of water, and add 200 mg of boric acid, 1 mL of nitric acid, and 1 mL of 0.1 N silver nitrate: any turbidity produced is not greater than that of a blank to which has been added 1.0 mL of 0.0010 N hydrochloric acid (0.012%).
Heavy metals: To 1 g, in a platinum dish or crucible, under a hood, add 1 mL of water and 3 mL of sulfuric acid, and heat at as low a temperature as practicable until all of the sulfuric acid has been expelled. Dissolve the residue in 20 mL of water, neutralize the solution to phph with ammonium hydroxide, add 1 mL of glacial acetic acid, dilute with water to 45 mL, filter, and use 30 mL of the filtrate for the test: the limit is 0.003%.
Assay: [NOTE—Store all solutions, except the Buffer solution, in plastic containers.]
Buffer solution: Dissolve 57 mL of glacial acetic acid, 58 g of sodium chloride, and 4 g of (1,2-cyclohexylenedinitrilo)tetraacetic acid in 500 mL of water. Adjust with 5 N sodium hydroxide to a pH of 5.25 ± 0.25, dilute with water to 1000 mL, and mix.
Standard preparations: Dissolve an accurately weighed quantity of USP Sodium Fluoride RS quantitatively in water to obtain a solution containing 420 µg per mL. Each mL of this solution (Standard preparation A) contains 190 µg of fluoride ion (10 2 M). Transfer 25.0 mL of Standard preparation A to a 250-mL volumetric flask, dilute with water to volume, and mix. This solution (Standard preparation B) contains 19 µg of fluoride ion per mL (10 3 M). Transfer 25.0 mL of Standard preparation B to a 250-mL volumetric flask, dilute with water to volume, and mix. This solution (Standard preparation C) contains 1.9 µg of fluoride ion per mL (10 4 M).
Assay preparation: Transfer about 100 mg of Sodium Fluoride, accurately weighed, to a 250-mL volumetric flask. Add 50 mL of water, mix for 5 minutes, dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a 50-mL volumetric flask, dilute with water to volume, and mix.
Procedure: Pipet 20 mL of each Standard preparation and of the Assay preparation into separate plastic beakers each containing a plastic-coated stirring bar. Pipet 20 mL of Buffer solution into each beaker. Concomitantly measure the potentials (see pH 791 ), in mV, of the solutions from the Standard preparations and of the solution from the Assay preparation, with a pH meter capable of a minimum reproducibility of ±0.2 mV and equipped with a fluoride-specific ion-indicating electrode and a calomel reference electrode. [NOTE—When taking measurements, immerse the electrodes in the solution, stir on a magnetic stirrer having an insulated top until equilibrium is attained (1 to 2 minutes), and record the potential. Rinse and dry the electrodes between measurements, taking care to avoid damaging the crystal of the specific-ion electrode.] Plot the logarithms of the fluoride-ion concentrations, in µg per mL, of the Standard preparations versus potential, in mV. From the measured potential of the Assay preparation and the standard response line, determine the concentration, C, in µg per mL, of fluoride ion in the Assay preparation. Calculate the quantity, in mg, of fluoride ion in each mL of the Oral Solution taken by the formula:
0.5(C / V)
in which C is the determined concentration of fluoride, in µg per mL, in the Assay preparation, and V is the volume, in mL, of Oral Solution taken.
Calculate the quantity, in mg, of NaF in the portion of Sodium Fluoride taken by the formula:
(41.99 / 18.998)(1.25C)
in which 41.99 is the molecular weight of sodium fluoride; 18.998 is the atomic weight of fluorine; and C is the determined concentration of fluoride, in microgm per mL, in the Assay preparation.
Molecular Formula: NaF
Formula Wt 41.99
CAS Number 7681-49-4
REQUIREMENTS
Assay: 99% NaF
MAXIMUM ALLOWABLE
Insoluble matter: 0.02%
Loss on drying at 150C: 0.3%
Chloride (Cl): 0.005%
Titrable acid: 0.03 meq/g
Titrable base: 0.01 meq/g
Sodium fluosilicate (Na2SiF6): 0.1%
Sulfate (SO4): 0.03%
Sulfite (SO2): 0.005%
Heavy metals (as Pb): 0.003%
Iron (Fe): 0.003%
Potassium (K): 0.02%
