Packaging and storage—
Preserve in tight containers.
Identification—
Solution:
25 µg per mL.
Medium:
methanol.
Absorptivities at 272 nm, calculated on the dried basis, do not differ by more than 3%.
Loss on drying 
731
—
Dry it in vacuum at 105
for 3 hours: it loses not more than 1.0% of its weight.
Heavy metals, Method I 231—
Dissolve 1.0 g in 20 mL of water in a separator, add 5 mL of 1 N hydrochloric acid, and extract with successive 20-mL, 20-mL, and 10-mL portions of methylene chloride. Discard the methylene chloride extracts, and use the aqueous layer for the test: the limit is 0.002%.
Free naproxen—
Dissolve about 5.0 g in 25 mL of water in a separator, and extract the solution with three 15-mL portions of chloroform. Evaporate the combined extracts on a steam bath to dryness. Dissolve the residue in 10 mL of a mixture of methanol and water (3:1) previously neutralized with 0.1 N sodium hydroxide to the phenolphthalein endpoint. Add phenolphthalein TS, and titrate with 0.10 N sodium hydroxide: not more than 2.2 mL is consumed (1.0%).
Chromatographic purity—
Dissolve 100 mg in 5 mL of methanol. Dissolve a suitable quantity of
USP Naproxen Sodium RS in methanol to obtain a
Standard solution having a known concentration of about 20 mg per mL. Dilute a portion of this solution quantitatively with methanol to obtain three
Comparison solutions having concentrations of 20, 60, and 100 µg per mL (0.1%, 0.3%, and 0.5% of the
Standard solution), respectively. Apply separate 10-µL portions of the five solutions on the starting line to a suitable thin-layer chromatographic plate (see
Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Develop the chromatogram in a solvent system consisting of a mixture of toluene, tetrahydrofuran, and glacial acetic acid (30:3:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber, mark the solvent front, air-dry, and view under short-wavelength UV light: the
RF value of the principal spot in the chromatogram of the solution under test corresponds to that of the
Standard solution, the intensity of any individual secondary spot does not exceed that of the 100-µg-per-mL
Comparison solution (0.5%), and the sum of the intensities of any secondary spots, similarly compared, does not exceed 2.0%.
Assay—
Dissolve about 200 mg of Naproxen Sodium, accurately weighed, in 50 mL of glacial acetic acid containing 2 drops of p-naphtholbenzein TS previously neutralized with 0.1 N perchloric acid if necessary. Titrate with 0.1 N perchloric acid VS. Each mL of 0.1 N perchloric acid is equivalent to 25.22 mg of C14H13NaO3.
-methyl-, sodium salt, (S)-.
)-Sodium (S)-6-methoxy-