Zwitterion-functionalized polymer microspheres-based solid phase extraction method on-line combined with HPLC-ICP-MS for mercury speciation.

Zwitterion-functionalized polymer microspheres (ZPMs) have been designed and used as the core adsorbent for the selective and rapid enrichment of mercury species in environmental waters by an on-line solid-phase extraction (SPE). Zwitterionic S-ZPMs and N-ZPMs having an anionic sulfonic group, but differing in cationic S and N moieties were prepared from Merrifield resin by treating with 1,2-ethanedithiol and imidazole, followed by modification with 1,3-propanesultone. Without any additional reagents, inorganic mercury (In-Hg), methylmercury (MeHg) and ethylmercury (EtHg) were quantitatively adsorbed on the home-made mini-column packed with ZPMs. Following extraction with 60 mM ammonium acetate and 0.15% L-cysteine (L-Cys) solution within seconds, separation and speciation of mercury were successfully achieved by the HPLC-ICP-MS technique. Under the optimized experimental conditions, the enrichment factors (EFs) are up to 105 and 98 for inorganic and organic mercury only with 40 mL sample solution, respectively. The low detection limits of 0.78 ng L, 0.63 ng L, and 0.49 ng L were reached for In-Hg, MeHg and EtHg, respectively, with the relative standard deviations (RSDs) below 4.1%. The feasibility and accuracy of the on-line SPE-HPLC-ICP-MS method were successfully applied for mercury speciation in surface water, seawater as well as certified reference material (CRM). The results here demonstrate a facile, sensitive and selective method for speciation of mercury at trace levels.