Novel Determination of Trace Copper (II) via Kinetic Spectrophotometry Combined with Online Separation Using a Core-Shell Polymer Inclusion Beads Extractor

A sensitive kinetic spectrophotometric method has been developed to determine copper concentrations in water samples. This method leverages the catalytic effect of Cu2+ to accelerate the redox reaction between thiourea and phosphomolybdic acid. Various reaction and operational parameters were investigated and optimized using both batch and flow experimental systems. To eliminate the interference of foreign ions, Cu2+ was separated from sample matrices using micro polymer inclusion beads (µPIBs)−a novel solid phase extractant fabricated with a microfluidic technology. The performance of various compositions and structures of µPIBs was compared. Core-shell µPIBs, fabricated with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the base polymer and 2-hydroxy-5-nonylacetophenone oxime (LIX 84I) as the carrier in the shell, exhibited exceptional performance. These particles achieved highly efficient extraction, while back-extraction with 0.1 M H2SO4 was quantitative and near-instantaneous. Under optimal conditions, a limit of detection of 0.7 µg L−1 for Cu2+ was achieved with a sample consumption of 0.5 mL and throughput of 58 h−1, and the interference of base metals was eliminated completely. This method is characterized by low blank absorbance and proneness to the change of reaction temperature, while offering high sensitivity. It has been successfully applied to Cu2+ determination in water samples, with results in good agreement with those obtained by ICP-MS.