Modified MWCNTs For Preconcentration Of Heavy Metals To On-line Inductively Couple Plasma Mass Spectrometry Determination

CNT were widely used as adsorbent for enrichment. CNT possessed intriguing properties, such as high chemical and thermal stability, superior mechanics, electromagnetism and optical properties, which was the most solid and stiffness materials. CNT had excellent adsorption capacity, which warranted their important applications in separation and preconcentration for metal ions. The selective adsorption of metal ions and adsorption effects of this material were greatly enhanced by functionalized MWCNTs.In this dissertation, a novel material was designed and prepared with functionalizing multi-walled carbon nanotubes (MWCNTs) using iminodiacetic acid (IDA) contained more acidic groups such as-COOH and-OH. The performance of new synthesized MWCNTs-IDA was studied and evaluated. The MWCNTs-IDA was characterized by ESI-MS and FT-IR. Then, Isotherm and kinetics of adsorption were studied and the experimental data fits the Langmuir model and pseudo-second-order equation very well. The novel material was employed to extract V (V), Cr (VI), Pb (II), Cd (II), Co (II), Cu (II) and As (III) from water and food samples prior to analysis by inductively coupled plasma mass spectrometry (ICP-MS).The MWCNTs-IDA demonstrated to be good adsorbent for separation and preconcentration of V (V), Cr (VI), Pb (Ⅱ), Cd (II), Co (II), Cu (Ⅱ) and As (III). Factors that influence the preconcentration procedure were optimized and studied, such as sample pH, sample flow rate. sample loading time and eluting solution. The results showed that, in weakly alkaline condition, V (V), Cr (VI), Pb (II), Cd (II), Co (II), Cu (Ⅱ) and As (III) were best adsorbed by MWCNTs-IDA, the optimum pH of sample solution was8.0, the enrichment factors for above metal ions were ranged from66to101. The linear range of the determination was0.001μg L-1～5μg L-1in aqueous solution. The detection limit (3SD) was found to be0.40～3.4ng L-1. The relative standard deviation of11replicate extractions of1.0μg L-1level were1.0-4.0%.The tolerance limit of coexistent ions was also investigated. The presence of10mg L-1(10000-fold) species K(I), Na(Ⅰ),5mg L-1(5000-fold) Ca(II), Mg(Ⅱ),0.4mg L-1(400-fold) Al(III), Fe(III) and4mg L-1(4000-fold) Mn(II), Zn(II) had no significant effect on the extraction and determination of1.0μg L-1V (V), Cr (VI), Pb (Ⅱ), Cd (Ⅱ), Co (Ⅱ), Cu (Ⅱ) and As (Ⅲ). The column was stable in operation process, enabling more than40adsorption-elution cycles without decreasing in the recoveries of the studied target ions.The recoveries of analyte spiked river water and food samples ranged from90to110%. The proposed method was validated by determination of analyte in certified reference materials and was shown to be promising for the determination of V (V), Cr (VI), Pb (Ⅱ), Cd (II), Co (II), Cu (II) and As (III) in real water and food samples.