Applying resonance Rayleigh scattering and spectrofluorimetric techniques for the selective determination of neomycin sulfate using Congo red as a probe: Applications for wastewater analysis.

Two simple, sensitive, and low-cost fluorescence spectroscopy methods for neomycin (NEO) detection were developed. Both methods were based on the interaction between NEO and Congo red (CR) in acidic buffer medium to form an ion-association complex. The quenching effect of the formed ion-association complex on the fluorescence of CR at 421 nm is a basic principle of fluorescence analysis, whilst the resonance Rayleigh scattering (RRS) method was used to enhance the resonance Rayleigh scattering spectrum at 384 nm by adding NEO. Experimental conditions such as pH, temperature, reaction time, CR concentration, and the ionic strength of the two methods were investigated and optimized. In addition, the effect of common coexisting substances on the method was tested and the results showed good selectivity. The composition of ion-association complexes, the reaction mechanism, and reasons for the enhanced intensity of RRS are discussed. Under optimum conditions, the responses of the fluorescence spectrophotometry and RRS methods showed good linearity with NEO concentrations in the range 0.2-3.0 μg ml and 0.1-3.0 μg ml , respectively. The detection limits of fluorescence spectrophotometry and RRS spectroscopy techniques were 0.02 μg ml and 0.01 μg ml , respectively. Finally, the two methods were applied to the analysis of wastewater and the results were satisfactory.