Trace determination of cadmium(ii) and copper(ii) in environmental water samples by solid-phase extraction using a novel ionic liquid-modified composite sorbent combined with flame atomic absorption spectrometry

Abstract

A sensitive and reliable analytical method for determination of trace Cd(II) and Cu(II) in environmental water was developed, based on solid-phase extraction (SPE) using a novel ionic liquid-modified composite as the sorbent combined with detection by flame atomic absorption spectrometry (FAAS). This new sorbent was prepared using a hydrophobic ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF₆]) immobilization onto the surface of nano-TiO₂ supported on fine glass beads, and characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Application of the sorbent was investigated for extraction and preconcentration of Cd(II) and Cu(II) from aqueous solutions as their chelates with 2-[(5-bromo-2-pyridyl)azo)-5-(diethl-amino) phenol (5-Br-PADAP). It was found that the adsorption of these chelates on the sorbent followed a Langmuir-type isotherm, and the adsorption kinetics were reasonably rapid. This novel SPE adsorbent allowed faster sample loading and higher extraction recovery than conventional nano-TiO₂ particles, and could be used repeatedly at least for 10 times without significant decrease in recovery of Cd(II) and Cu(II). The parameters that affect the SPE recovery of both metal ions were examined. The optimum conditions, including sample pH, eluent type and volume, as well as sample and eluent flow rates were obtained. The detection limits were 0.1 and 0.3 μg L⁻¹, and the intra-day relative standard deviations (RSDs, n = 6) were 2.0% and 1.4% for Cd(II) and Cu(II), respectively. The proposed method was successfully applied to the determination of trace amounts of Cd(II) and Cu(II) in environmental water samples.