Analytical Application of Resonance Rayleigh Scattering, Frequency Doubling Scattering, and Second-Order Scattering Spectra for the Sodium Alginate-CTAB System

Abstract

Three new methods for the determination of trace amounts of sodium alginate (SA) based on the reaction of SA with cetyltrimethylammonium bromide (CTAB) by resonance Rayleigh scattering (RRS), frequency doubling scattering (FDS), and second-order scattering (SOS) have been investigated. The SA can react with CTAB in a pH 10.0 Britton–Robinson buffer to form a new product, which can lead to a significant enhancement of RRS, FDS, and SOS intensities and appearance of new spectra. The maximum scattering wavelengths, λex/λem, appear at 351 nm/351 nm for RRS, 240 nm/480 nm for SOS, and 870 nm/435 nm for FDS, respectively. The increments of the scattering intensities (ΔI) are proportional to the concentration of SA in a certain range. The detection limits (3σ) for SA are 3.69 ng mL⁻¹ for the RRS method, 6.91 ng mL⁻¹ for the FDS method, and 7.45 ng mL⁻¹ for the SOS method under optimum conditions. The proposed methods were applied to the determination of SA in real samples with satisfactory results.

Keywords:

• CTAB
• Frequency doubling scattering
• Resonance Rayleigh scattering
• Second-order scattering
• Sodium alginate

Acknowledgments

This project is supported by the National Natural Science Foundation of China (No. 20575054) and the Municipal Science Foundation of Chongqing City (No. CSTC–2008BB4013).