Spectrophotometric determination of naproxen in pure and pharmaceutical preparations

Naproxen reacts with 1-naphthylamine and sodium nitrite to give an orangish red colour having maximum absorbance at 460-480 nm (working wavelength 480 nm). The reaction is selective for naproxen with 0.001 mg/ml as visual lim it of quantitation and provides a basis for a new spectrophotometric determ ination. The reaction obeys Beer's law from 0.01 mg to 6.5 mg/10 ml of napr oxen and the relative standard deviation is 1.5%. The quantitative assessme nt of tolerable amount of other drugs is also studied.