Online coupling of ultraviolet titanium dioxide film reactor with poly(methyl methacrylate) solid phase extraction-inductively coupled plasma mass spectrometry for speciation of trace heavy metals in freshwater

摘要

To rapidly discriminate dissolved labile and stable organic-complexed metal ions, a fully automated approach comprising a photocatalyst-assisted digestion reactor (PADR), a non-functionalized poly(methyl methacrylate) (PMMA) solid-phase extraction (SPE) column, and inductively coupled plasma-mass spectrometry (ICP-MS) instrumentation was developed. To separate labile dissolved metals from other concomitant metal complexes, a non-functionalized PMMA bead was used as the SPE adsorbent because of its selective interaction with labile metal ions. The PMMA SPE-ICP-MS hyphenated system was optimized, and its analytical reliability was confirmed by using it to analyze the certified reference material-NIST 1643e (artificial saline water). Detection limits (σ=3, n=7) for all analyte ions (Ni, Cu, Zn, Cd, and Pb), which ranged from 0.005 to 0.186μgL~(-1), could be reached; therefore, this technique appeared uniquely suited to determining levels of trace elements in most natural freshwater samples. To determine the total quantity of dissolved metals, a new digestion reactor (PADR) was developed for online conversion of metal-organic complexes to their labile forms. Compared to conventional photolysis methods, the digestion time improved considerably and the digestion efficiency for organic substances was excellent (>90%) in the PADR format, with a very short resident time of 10min. After construction of the PADR-PMMA SPE-ICP-MS hyphenated system, the speciation potential of our developed method was evaluated by analyzing three intentionally contaminated water samples. Results indicated that our developed hyphenated system is effective for online determination of total, labile, and metal-humic complexes in freshwater samples and that is capable of providing representative metal speciation patterns for different aquatic systems.