Quantitation of naproxen by quenching of phosphorescence from a ternary complex of 2-bromo-6-methoxynaphthalene and α-cyclodextrin

A unique method, based on the measurement of phosphorescence lifetimes, is reported for use in analytically detecting the widely used anti-inflammatory drug naproxen. The reciprocal phosphorescence lifetime of a ternary complex containing α-cyclodextrin and 2-bromo-6-methoxynaphthalene increases linearly with naproxen concentration and has a quenching constant of 2.1 ± 0.05 × 10⁶ M⁻¹ s⁻¹. Similar behavior is observed for quenching by the sodium salt of naproxen that has a quenching constant of 1.8 × 10⁶ ± 0.05 M⁻¹ s⁻¹. The experimental sensitivity is sufficient to permit measurements of naproxen concentrations differing by 11 μg/ml. Phosphorescence lifetime measurements reveal that the quenching mechanism does not involve displacement of the unrelaxed triplet-state guest molecule by naproxen from the complex and may occur by energy transfer or electron transfer.