Abstract: In pH 5.3—6.8 Britton-Robinson(BR) buffer medium, Cefotaxime sodium(CFTM) can react with HgCl₂ to form 1∶1 anionic chelate, which can further react with basic triphenylmethane dye such as crystal violet, methyl violet, ethyl violet, brilliant green, iodine green, methyl green and malachite green to form ternary ion-association complexes. As a result, the resonance Rayleigh scattering(RRS) spectrum was enhanced greatly. The maximum RRS wavelengths of three ion-association complexes were located at 367, 367, 340, 367, 340, 340 and 340 nm, respectively. The increments of scattering intensity(ΔI) were directly proportional to the concentrations of CFTM in certain ranges. The linear ranges and the detection limits(3σ) of CFTM for seven systems were 0.0090—3.5 μg/mL and 2.7 ng/mL(crystal violet), 0.0092—3.5 μg/mL and 2.8 ng/mL(methyl violet), 0.013—3.5 μg/mL and 4.0 ng/mL(ethyl violet), 0.010—3.5 μg/mL and 3.1 ng/mL(brilliant green), 0.011—3.5 μg/mL and 3.4 ng/mL(iodine green), 0.012—4.0 μg/mL and 3.5 ng/mL(methyl green), and 0.016—3.5 μg/mL and 4.7 ng/mL(malachite green), separately. The sensitivity of crystal violet system was higher than those of other six systems. The optimum conditions and the influence factors were investigated, and the composition of ion-association complexes and the reaction mechanism were also discussed. The effects of foreign substances were tested and it is shown that the method has a good selectivity. Based on HgCl₂ and basic triphenylmethane dye, the sensitive, simple and rapid method for the determination of trace CTRX was developed.

Key words: Resonance Rayleigh scattering, Cefotaxime sodium, HgCl₂, Basic triphenylmethane dye