Selective extraction and release using (EDTA-Ni)-layered double hydroxide coupled with catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine for sensitive detection of copper ion

Copper is an important heavy metal in various biological processes. Many methods have been developed for detecting of copper ions (Cu2+) in aqueous samples. However, an easy, cheap, selective and sensitive method is still desired. In this study, a selective extraction-release-catalysis approach has been developed for sensitive detection of copper ion. Ethylenediaminetetraacetic acid (EDTA) chelated with nickel ion (Ni2+) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent in dispersive solid-phase extraction for the enrichment of Cu2+ at pH 6. Since Cu2+ has a stronger complex formation constant with EDTA, Ni2+ exchanged with Cu2+ selectively. The resulting sorbent containing Cu2+ was transferred to catalyze the 3,3',5,5'-tetramethylbenzidine oxidation reaction, since Cu2+ could be released by the sorbent effectively and has high catalytic ability for the reaction. Blue light emitted from the oxidation product was measured by ultraviolet-visible spectrophotometry for the determination of Cu2+. The extraction temperature, extraction time, and catalysis time were optimized. The results showed that this method provided a low limit of detection of 10 nM, a wide linear range (0.05-100 mu M) and good linearity (r(2) = 0.9977). The optimized conditions were applied to environmental water samples. Using Cu2+ as an example, this work provided a new and interesting approach for the convenient and efficient detection of metal cations in aqueous samples. (C) 2015 Elsevier B.V. All rights reserved.