Determination of Cr(VI) by Solid-Phase Extraction with Highly Selective Resin

Solid-phase extraction using molecular recognition technology (SPE-MRT) was done by using a chemically modified silica gel with covalently bound ligand polyatomic donor. Its highly selective adsorption behavior towards target elements was examined. The MetaSEP AnaLig® Cr-02 and AN-02 resins could adsorb Cr(VI), which contains chromate (CrO4)2- and dichromate (Cr2O7)2- species, from a Cr(III) and Cr(VI) matrix solutions. Further investigation showed that the Cr(VI) species was quantitatively collected in the pH range of 0∼6, whereas Cr(III) could not be retained on the resin in an acidic region (pH < 4). On the other hand, the InertSep® ME-1 synthesized methacrylate co-polymer resin with chelating function, imino-di-acetate group, could adsorb Cr(III) at a neutral region (pH 5∼7), and did not adsorb selectivity towards Cr(VI) at acidic to neutral region (pH 0∼7). Determinations of Cr(III) and Cr(VI) were carried out by ICP-AES. Cr(VI) was also determined by using a diphenyl-carbazide colorimetric assay analysis with a UV/VIS spectrophotometer at 540 nm. To explore the merit of MRT resin, the speciation of chromium was demonstrated by using an automated SPE workstation, MetaPREP APS-1, whose metal parts were replaced with PEEK and a high-purity graphite tip needle. The SPE-MRT resins were packed in disposable polypropylene (PP) mini-columns and utilized as on-line connector devices with a sealing cap on the SPE cartridges, which were installed serially in the newly laboratory-assembled SPE automation. An Auto Pre-treatment System (APS) with ICP-AES and a UV/VIS spectrophotometer could provide highly sensitive determination for the speciation of Cr(III) and Cr(VI). The proposed system was successfully applied to the determination of Cr(VI) in spiked actual industrial wasted water and soil extract samples.