Resonance Rayleigh scattering methods for the determination of chitosan with Congo red as probe

Two methods were presented for the sensitive and selective determination of chitosan (CTS) with Congo red (CR) as probe based on resonance Rayleigh scattering (RRS) intensities in health products. In weakly acidic buffer solution, the binding of CTS to CR, could result in the enhancement of the RRS intensities. Moreover, after adding OP emulsifier (octyl‐phenyl polyoxyethylene ether) to the system, the RRS intensities showed more significantly enhancement. The maximum RRS signals for the CTS–CR system and the CTS–CR–OP system were located at 380 nm and 376 nm, respectively. Under optimum experimental conditions, the increased RRS intensities (ΔI) of these two systems were linear to CTS concentration in the range of 0.40–8.00 μg/ml and 0.05–1.00 μg/ml. Their limits of detection (LOD) were 44.81 ng/ml and 6.99 ng/ml, which indicated that the latter system was more sensitive than the former. In this work, the optimum conditions and the effects of some foreign substances on the determination were studied. In addition, the effect of the molecular weight of CTS and the reasons for the enhancement of resonance light scattering were discussed. Finally, these two methods were applied to the determination of chitosan in health products with satisfactory results.