Determination of cobalt(II) by resonance Rayleigh scattering and resonance non-linear scattering with alizarin red S as probe

In HAc-NaAc buffer medium at pH 5.4,Co(Ⅱ) could react with alizarin red S and cetylpyridinium bromide to form hydrophobic ternary ion association complex with large particle size through electrostatic attraction and hydrophobic force,leading to the significant enhancement of resonance Rayleigh scattering(RRS),second order scattering(SOS)and frequency doubling scattering(FDS)of system.The maximum scattering peak(λex/λem)was located at 380nm/380nm(RRS),289nm/578nm(SOS)and 620nm/310nm(FDS),respectively.Under the optimal conditions,the intensity change of three scattering lights(ΔIRRS,ΔISOSandΔIFDS)showed linear relationship with the mass concentration of Co(Ⅱ) in range of 0.08-19.25,0.14-16.42 and 0.14-17.78μg/mL,respectively.Meanwhile,the system exhibited high detection sensitivity.The detection limit(3σ)of Co(Ⅱ) was 1.6(RRS),2.3(SOS)and 2.8ng/mL(FDS),respectively.The influence of interaction between Co(Ⅱ) ,alizarin red S and cetylpyridinium bromide on the spectral characteristic and intensity of RRS,SOS and FDS was investigated.RRS was used as an example to study the effect of solution medium,pH and resonance probe dosage on the scattering system.The stability of scattering reaction and the influence of coexisting materials were investigated.Moreover,the cause to scattering enhancement and the reaction mechanism were also discussed.The proposed method was applied to the determination of Co(Ⅱ) in water sample,and the found results were consistent with those obtained by the standard method.The relative standard deviation(RSD)was no more than 2.5%.