Determination of cadmium in water samples by stir bar sorptive–dispersive microextraction and flame atomic absorption spectrometry

Stir bar sorptive–dispersive microextraction (SBSDµE), has been applied as a novel, fast and simple method, for the preconcentration and determination of trace amounts of Cd (II) ions in water samples. SBSDµE is a new microextraction technique that combines the principles of stir bar sorptive extraction (SBSE) and dispersive micro solid phase extraction (DµSPE). In this method magnetic sorbent, that magnetically is coated on a neodymium stir bar, dispersed in the sample solution at high stirring rate as DµSPE method and re-atrracted to magnetic bar when stirring is stopped alike SBSE. Then stir bar is eluted by an appropriate solvent, which is used for analysis. This approach is benefited from the advantages of SBSE and DµSPE, including high extraction recovery, no need to an external stirring device that avoids potential analytes losses, easy to apply, lower extraction time because of dispersion of sorbent in sample solution and more variety sorbents by using different coated magnetic composites [1]. In this work, Fe3O4@SiO2@ZnO core–shell microspheres that have been used as magnetic sorbent were prepared by a simple three-step method. The synthesized composite was characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis that illustrated Fe3O4 microspheres coated with two distinct nanolayers, silica and ZnO [2]. After elution of stir bar by proper solvent, cadmium ions were determined in eluent by flame atomic absorption spectrometry (FAAS). The effective factors on extraction of Cd (II) were investigated and optimized. For optimization of adsorption conditions (pH, stirring rate, salt effect and extraction time), response surface methodology (RSM) was used as a strong statistical technique. Elution condition(type of eluent, eluent concentration, eluent volume and elution time) were optimized with one variable at a time optimization method. Under the optimal conditions, linear range of SBSDµE method was 1-150 ng mL-1, the relative standard deviations ( RSD% ) at 80ng mL−1 concentration level was 3.7% (n=5), the limit of detection was 0.37ng mL-1. The proposed microextraction analytical method was successfully used for determination of ultra trace amounts of cadmium in water samples (tap water, river and well).