In pH 0–1.0 HCl medium, 12-tungstophosphoric acid (TP) could react with vitamin B1 (VB1) to form a 1 : 3 ion-association complex. As a result, new spectra of resonance Rayleigh scattering appeared and their intensities were enhanced greatly. The maximum wavelength was located at 335 nm. The scattering intensities were proportional to the concentration of VB1 in the range of 0.25–1.75 μg mL−1. Therefore, a new method for the determination of VB1 was established. The method had high sensitivity and good selectivity, and the detection limit (3σ) was 0.94 ng mL−1. It was applied to the determination of VB1 in urine samples and VB1 tablets, which showed that the results were consistent with those of the China pharmaceutical method. The recovery was between 97.3%–99.0%, and the relative standard deviation (RSD) was between 1.1%–3.4%. Furthermore, the optimum reaction conditions, the RRS spectra characteristics, the reaction mechanism and the reasons for enhancement of scattering were evaluated.
