A simple technique for the detection of low concentrations of chromium(VI) was developed based on the surface enhanced Raman spectroscopy (SERS). By the hydrogen-bond of water between chromium(VI) and the carboxyl groups from mercaptobenzoic acid (MBA) attached to the Au plate surface and Au nanoparticles, the sandwich structure of "MBA modified Au plate substrate/chromium(VI)-water/MBA modified Au nanoparticles" was built for SERS detection. The existence of chromium(VI) ions was monitored by detecting the SERS signals of the reporter molecules. The results reveal that the SERS intensities of the reporter were relevant to the concentration of chromium(VI) ions. The SERS intensities changed non-linearly with the increase of the concentration and a significant increase in the SERS signal was observed on the concentration of 10^－9 mol/L. Based on the above sandwich structure, functionalized Fe₂O₃@Au core-shell magnetic nanoparticles was introduced to enrich and separate chromium(VI) ions by the assistance of an external magnetic field. SERS detection showed that the concentration of chromium(VI) ions reduced by about 4～6 orders after the magnetic separation for the initial solution of 10^－5 mol/L.

Key words: chromium(VI) ions, surface enhanced Raman spectroscopy (SERS), Au nanoparticles, magnetic separation