Abstract:

A new dual-wavelength overlapping resonance Rayleigh scattering (DWO-RRS) method was developed to detect vitamin B₁₂(VB₁₂) with 12-tungstophosphoric acid(TP). In a HCl medium(pH=1.0), VB₁₂ could react with TP to form a 3: 1 ion-association complex. As a result, the new spectra of DWO-RRS, second order scattering(SOS) and frequence doubling scattering(FDS) appeared and their intensities were enhanced greatly. Their maximum wavelengths were located at 330 nm(RRS), 370 nm(RRS), 608 nm(SOS) and 386 nm(FDS), respectively. The three kinds of scattering intensities(ΔI_RRS, ΔI_SOS and ΔI_FDS) were proportional to the concentration of VB₁₂ in certain ranges. The methods had high sensitivity with the detection limit of 2.0-7.6 ng/mL. The optimal conditions and the effects of coexistent substances of RRS method were investigated. So, a simple, rapid and new method had been proposed to determine trace VB₁₂. It had been applied to the determination of VB₁₂ in urine samples and vitamin B₁₂ tablets with satisfactory results. In addition, the reasons for RRS enhancement and composition of ion-association complex were discussed.

Key words: Vitamin B₁₂, 12-Tungstophosphoric acid, Dual-wavelength overlapping resonance Rayleigh scattering, Second order scattering, Frequence doubling scattering