(na prox' en).
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C14H14O3 230.26

2-Naphthaleneacetic acid, 6-methoxy--methyl-, (S)-.
(+)-(S)-6-Methoxy--methyl-2-naphthaleneacetic acid [22204-53-1].
» Naproxen contains not less than 98.5 percent and not more than 101.5 percent of C14H14O3, calculated on the dried basis.
Packaging and storage— Preserve in tight containers.
USP Reference standards 11
USP Naproxen RS Click to View Structure
B: Ultraviolet Absorption 197U
Solution: 25 µg per mL.
Medium: methanol.
Absorptivities at 271 nm, calculated on the dried basis, do not differ by more than 3%.
Specific rotation 781S: between +83.0 and +89.5.
Test solution: 10 mg per mL, in methyl isobutyl ketone.
Loss on drying 731 Dry it at 105 for 3 hours: it loses not more than 0.5% of its weight.
Chromatographic purity— Dissolve 100 mg of Naproxen in methanol, and dilute with methanol to 5.0 mL to obtain the Test solution. Dissolve a suitable quantity of USP Naproxen 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 and stepwise 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 to the starting line of 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 Test solution corresponds to that of the Standard solution, and any other spot obtained from the Test solution does not exceed, in size or intensity, the principal spot obtained from 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 500 mg of Naproxen, accurately weighed, in a mixture of 75 mL of methanol and 25 mL of water that has been previously neutralized to the phenolphthalein endpoint with 0.1 N sodium hydroxide. Dissolve by gentle warming, if necessary, add phenolphthalein TS, and titrate with 0.1 N sodium hydroxide VS. Each mL of 0.1 N sodium hydroxide is equivalent to 23.03 mg of C14H14O3.
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