Spectroscopic studies on the interaction between norfloxacin and p-amino benzoic acid: analytical application on determination of norfloxacin.

Fluorescence (Förster) Resonance Energy Transfer (FRET) between norfloxacin (NF) and p-amino benzoic acid (PABA) has been investigated by fluorescence and UV-vis absorption spectroscopy. It was found that the quenching of fluorescence of PABA is followed by simultaneous sensitization of NF fluorescence. The hydrophobic and electrostatic interaction plays an important role to stabilize the complex. The binding constant (K), binding site number (n) and corresponding thermodynamic parameters like free energy change (DeltaG), enthalpy change (DeltaH) and entropy change (DeltaS) were determined according to van't Hoff equation. Using FRET, the distance (r) between donor (PABA) and acceptor (NF) was obtained. This method is simple, selective and relatively free of interference from co-existing substances. The method was successfully applied to the determination of norfloxacin from pharmaceutical tablets.