Preparation,Characterization, and Application of L‐Cysteine Functionalized Multiwalled Carbon Nanotubes as a Selective Sorbent for Separation and Preconcentration of Heavy Metals

L ‐cysteine functionalized multi‐walled carbon nanotubes (MWCNTs‐cysteine) are synthesized and characterized by XPS, FT‐IR, XRD, and TEM. The capability of MWCNTs‐cysteine for selective separation and preconcentration of heavy metal ions are statically and dynamically evaluated with Cd²⁺ as a model heavy metal ion. Unlike MWCNTs, the sorption of Cd²⁺ onto MWCNTs‐cysteine is not influenced by ionic strength in a wide range. The MWCNTs‐cysteine is demonstrated to be good column packings for on‐line microcolumn separation and preconcentration of Cd²⁺. Effective preconcentration of Cd²⁺ on the MWCNTs‐cysteine packed microcolumn is achieved in a pH range of 5.5 to 8.0. The retained Cd²⁺ is efficiently eluted with 0.5 mol L^?1 HCl for on‐line flame atomic absorption spectrometric determination. The MWCNTs‐cysteine exhibit fairly fast kinetics for the adsorption of Cd²⁺, and offer up to 1600‐fold improvement of the tolerable concentrations of co‐existing metal ions over the MWCNTs for on‐line solid‐phase extraction of Cd²⁺. With a preconcentration time of 60 s at a sample loading flow rate of 5.0 mL min^?1, an enhancement factor of 33 and a sample throughput of 36 h^?1 along with a detection limit (3s) of 0.28 µg L^?1 are obtained. The precision (RSD) for 11 replicate measurements is 1.6% at the 10 µg L^?1 level. The developed method using the MWCNTs‐cysteine as sorbent is successfully applied to determination of trace cadmium in a variety of biological and environmental materials.