Novel and sensitive methods for the determination of dopamine based on the resonance Rayleigh scattering, second-order scattering and frequency doubling scattering quenching effects.

Three novel methods were designed for the determination of dopamine (DA) by means of the quenching effects on resonance Rayleigh scattering (RRS) and non-linear scattering such as second-order scattering (SOS) and frequency doubling scattering (FDS) intensities. In Britton-Robinson buffer medium (pH 6.02), I(3)(-) could react with DA to produce I(-), which resulted in the decreases of the RRS, SOS and FDS intensities of the ethyl violet (EV)-I(3)(-) system, and the decreases of scattering intensity (DeltaI) were directly proportional to the concentrations of DA in a certain range. The detection limit (3sigma) for DA was 0.0195 micromol/L for the RRS method, 0.286 micromol/L for the SOS method and 0.0985 micromol/L for the FDS method, respectively. In this work, the characteristics of absorption, RRS, SOS and FDS spectra of this reaction have been studied; the optimum reaction condition and influencing factors have been investigated. The methods were applied to the determination of DA in pharmaceutical samples with satisfactory results.