Spectrofluorimetric determination of trace nitrite with a novel fluorescent probe

A simple, sensitive and selective fluorimetric determination for trace nitrites was developed using an unsymmetrical rhodamine with a high fluorescence quantum yield and large Stokes shift. The method is based on the reaction of the unsymmetrical rhodamine with nitrite in an acidic medium to form a nitroso product, which has much lower fluorescence because the electron-withdrawing effect of the nitroso group influences the system of p-π conjugation between N atom and benzene ring. Under optimum conditions, the fluorescence quenching intensity is linear over a nitrite concentration range of 1.0 × 10−8 to 3.5 × 10−7 M. The detection limit is 2.0 × 10−10 M (S/N = 3). The method was applied to the determination of nitrite in tap water and lake water with satisfactory results. The mechanism for the reaction is also reported.