Magnetism-assisted in-tube solid phase microextraction for the on-line chromium speciation in environmental water and soil samples

In the present study, a new method for chromium speciation was proposed by on-line coupling of magnetismassisted in-tube solid phase microextraction (MA/IT-SPME) with high-performance liquid chromatographydiode array detector (HPLC-DAD). Firstly, Cr(III) and Cr(VI) were coordinated with ammonium pyrrolidinedithiocarbamate (APD) to form Cr(III)/APD and Cr(VI)/APD complexes, separately. After that, a microextraction column based on porous monolith doped with magnetic nanoparticles was in situ fabricated in a capillary. The microextraction column was twined with a magnetic coil which was employed to engender changeable magnetic fields during extraction period. Various main factors influencing the extraction performance were inspected in detail. Results well indicated that the implementation of the magnetic field could assist the enhancement of extraction efficiency for Cr(III)/APD (80.4%) and Cr(VI)/APD (86.2%) complexes. Under the optimized parameters, the limits of detection for Cr(III) and Cr(VI) in water sample were 0.0059 ?g/L and 0.0020 ?g/L, respectively, and the corresponding values in soil sample were 0.47 ?g/kg and 0.057 ?g/kg, separately. The enrichment factors were 59 and 72 for Cr(III) and Cr(VI), respectively. The successful quantification of Cr(III) and Cr(VI) at trace levels in environmental water and soil samples well demonstrated the reliability and practicality of the proposed on-line approach for chromium speciation.