A novel method for detecting allura red based on triple-wavelength overlapping resonance Rayleigh scattering

Abstract

A method is presented for the sensitive and selective determination of trace allura red (AR) with ethyl violet (EV) in drink samples, based on triple-wavelength overlapping resonance Rayleigh scattering (TWO-RRS). At pH 10.0 in a Britton–Robinson (BR) buffer medium, AR combined with EV to form an ion-association complex, which resulted in the RRS intensity getting enhanced significantly with new RRS peaks appearing at 341, 508 and 666 nm. The scattering intensities of the three peaks were proportional to the concentration of AR in the range of 0.057–5.0 μmol L⁻¹ (0.028–2.48 μg mL⁻¹). The detection limits for the three single peaks were 0.048 μmol L⁻¹ (0.024 μg mL⁻¹), 0.050 μmol L⁻¹ (0.025 μg mL⁻¹), and 0.057 μmol L⁻¹ (0.028 μg mL⁻¹), while that of the TWO-RRS method was 0.017 μmol L⁻¹ (0.008 μg mL⁻¹), indicating that the TWO-RRS method could detect trace AR with high sensitivity. In addition, the optimum reaction conditions and the effects of foreign substances were studied. The composition of the ion-association complex, and the reasons for the enhancement of RRS were also investigated. The proposed method was successfully applied in a real sample analysis with satisfactory results.