Preconcentration of Trace Amounts of Zinc and Copper from Water Samples onto Polystyrene Foils Prior to Determination by Wavelength-Dispersive X-ray Fluorescence Spectrometry

A simple method of determining trace amounts of zinc (Zn) and copper (Cu) by wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) is proposed. The method is based on the preparation of special foils enriched with specified trace elements. In the first step, the elements were preconcentrated by liquid-liquid extraction using dithizone in CCl₄. In the second step, the obtained extracts containing determined elements were mixed with a solution of polystyrene in CH₂Cl₂. After the evaporation of the organic solvents the produced foils were peeled off the Petri dish and analyzed by WDXRF. The method of preconcentration of trace amounts of Zn and Cu as well as the procedure of obtaining suitable foils for XRF measurements were optimized. We studied the effects of parameters such as the amounts of complexing agent and selected interfering elements, pH, and volume of analyte solutions on the recovery of Zn and Cu in the extraction process and their determination. The homogeneity of the mass per unit area of the prepared foils was evaluated using the internal standard method. The proposed method allows determination of trace amounts of Zn and Cu with about 98% recovery and 7 ng mL⁻¹ detection limits for 250 mL of water. The method is useful for routine determination of trace metals in aqueous samples by X-ray fluorescence spectrometry.