Microemulsion High Performance Liquid Chromatographic Analysis Of Co²⁺, Cu²⁺, Ni²⁺, Fe³⁺

In this article, a study was made on precolumn derivative condition of metallic ions, including Co²⁺, Cu²⁺, Ni²⁺, Fe³⁺ ions and simultaneous determination by the microemulsion high performance chromatography. The behaviors in the chromatogram of the complex of these four metals were analyzed. The conditions of the separation and determination were optimized. 2 - (5 - bromo -2 - pyridylazo) -5-diethylaminophenol (5-Br-PADAP) was used as a precolumn chelating reagent, The four metal ions were properly separated in 15 minutes on a C18 column with microemulsion -acetonitrile, a mobile phase (35:65, V/V with pH5.3 HAc-NaAc buffer solution), column temperature of 30℃, flow rate of 1.2mL/min and measured wave length of 560nm.The conventional acetonitrile–water (including a certain concentration of CTMAB) as mobile phase, chromatographic peaks of Co²⁺,Cu²⁺,Ni²⁺ and Fe³⁺ were seriously superposed. In order to improve separation effect of the four irons, microemulsion was proposed as the mobile phase for the experiment. When the microemulsion-acetonitrile acted as mobile phase, the separation degree of the metal complex was more than 1.5. They were separated within 15 minutes. And the peak areas of each metal complex were obviously increased, which were more than the ones during the mobile phase analysis with acetonitrile–water. This method got larger quantity of allowable coexisting ions, more selections, relative standard deviations of less than 5% and a good precision. The linear of range for the determination of Co²⁺, Cu²⁺, Ni²⁺, Fe³⁺ were 0.07 3.2μg/mL, 0.09 4.0μg/mL, 0.08 2.4μg/mL, 0.2 2.4μg/mL.The detection limits (μg/L) were: 7.712 for Co²⁺, 8.186 for Cu²⁺, 9.615 for Ni²⁺, 20.11 for Fe³⁺.The method was applied to determination of Co²⁺, Cu²⁺, Ni²⁺, Fe³⁺ in the river water, tea and Chinese medicine. The recovery rates of each metal ion were 87.2 98.3%, this method does have characters of better separation effect, rapid analysis and high sensitiveness. Viscosity of the microemulsion was determined, and its principle was discussed preliminarily.