Carbon nanotube-based magnetic bucky gels in developing dispersive solid-phase extraction: application in rapid speciation analysis of Cr(VI) and Cr(III) in water samples

In this work, we developed dispersive solid-phase extraction method with the use of carbon nanotube based magnetic bucky gels. The hydrophilic carbon nanotube (CNT)-based magnetic bucky gels (M-BGs) were developed with the features of magnetic susceptibility to permit fast injection of sorbent, rapid retrieval of the sorbent and high dispersion of MWCNT in the aqueous sample. We combined magnetic multi-wall carbon nanotube nanocomposite (MMWCNTs) with hydrophilic ionic liquids in order to prepare highly stable carbon nanotube-based magnetic bucky gels. The hydrophilic ILs act simultaneously as modifier and disperser for MMWCNTs and reduce the agglomeration of sorbent in water .Consequently they enhance the extraction efficiency. We used the unique features of this responsive gel (fluidity, stability, magnetic properties, and strong sorbing ability) in developing a new, fast, sensitive, simple, and environmental-friendly magnetic bucky gel-based dispersive solid-phase extraction method (M-BG-dSPE) combined with fibre optic linear array detection spectrophotometer (FO-LADS) for preconcentration and speciation of Cr(VI) and Cr(III) in water samples. The properties of MMWCNT and magnetic bucky gels were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectrophotometer (FT-IR). Under the optimised conditions, the enrichment factor of the method was 318, the limit of detection was 0.1ng mL(-1) and the repeatability of the method, expressed as the relative standard deviation (RSD, n=5), varies between 3.2% and 2.5% in different concentrations. The proposed procedure has been applied for speciation of Cr(VI) and Cr(III) in water samples with good recoveries in the range from 90 to 105%. Validation of the method was carried out by comparison of the obtained results with results obtained by the ET-AAS and spiking-recovery method.