Ion Associating Spectrophotometric Determination Of Trace Cadmium

The high concentration I-and Cd²⁺can form [CdI₄]^2-, and then generate ionassociation complex with basic dyes of three benzene methane. This paper based thistheory, studied the best condition of Acriflavine in water phase photometric method andRhodamine B, Butyl rhodamine B in two water phase extraction.In the pH3.6HAc-NaAc buffer solution, Polyvinyl Alcohol used as surfactant,acridine yellow and [CdI₄]^2-form stable ion-association complex. The maximumabsorption wavelength of this ion-association complex is at294nm and its apparentmolar absorption coefficient reaches3.0×105L·mol^-1·cm^-1, concentration of cadmium inthe Beer law is obeyed in the range of0～25μg·L^-1. The method is high selective andsensitive. Applied directly to the determination of cadmium for copper-cadmium slag,the relative standard deviation is4.5%, and the result is satisfied.In the presence of ammonium sulphate, the extraction behavior of Cd（II） based onpotassium iodide-Rhodamine B-alcohol system was studied and proper condition ofphase separation was selected. Results showed that, in the pH1-3environment, theextraction rate of [CdI4]2-by alcohol-ammonium sulfate aqueous two-phase system isonly35.5%, and the ion association complex, which is formed by adding rhodamine B,can be extracted completely by the aqueous two-phase system. In the system, Cd²⁺canbe dissociated completely from Zn²⁺, Fe³⁺, Co²⁺, Cu²⁺and Ni²⁺.In the0.5mol·L^-1H2SO4medium, cadmium-potassium iodide-Butyl Rhodamine Bformed stable blue ion association complex in alcohol-ammonium sulfate aqueoustwo-phase system. Its apparent molar absorption coefficient reaches1.28×106L·mol^-1·cm^-1, concentration of cadmium in the Beer law is obeyed in the range of0～3μg/10mL cadmiumand and the correlation coefficient is0.9984. Under optimalextraction conditions, the maximum extraction rate of the ion association complex is98%, and Cd²⁺can be dissociated completely from Zn²⁺, Fe³⁺, Co²⁺, Cu²⁺and Ni²⁺. Thismethod is not only high sensitivity and selectivity, but also environmentally friendly,simple, rapid, phase clear without stripping, and high practical.Ion association system can not only great improve the reaction sensitivity, but alsosatisfy the stability. Aqueous two-phase extraction technology has many advantages,such as clear, no reverse extraction, environmental protection, operating easy, andsensitivity and selectivity is good. So it will be the development trend of the technologyof separation in the next few years.