Noble metal nanocomposites as tools for fast and reliable speciation analysis of mercury in water samples

A novel non-chromatographic approach for speciation analysis of mercury was developed based on sequential application of silver and gold nanocomposites as sorbents for solid phase extraction. The nanocomposite materials consisted by AgNPs or AuNPs grafted on submicronsized silica spheres (SiO2-NH2@AgNPs and SiO2-NH2@AuNPs) were prepared by multistep synthesis procedures and characterised in details by different techniques - Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), electrokinetic measurements, UV-Vis spectroscopy and X-ray diffraction. Excellent separation and enrichment of Hg(II) and CH3Hg+ was achieved due to the specific behaviour and affinity of Ag and Au nanoparticles (NPs) towards particular Hg chemical forms. In the first extraction step, Hg(II) was strongly retained by highly selective amalgamation on the surface of Ag nanocomposite (SiO2-NH2@AgNPs). In the second extraction step, CH3Hg+ remained in the supernatant solution was sorbed on the surface of Au nanocomposite (SiO2-NH2@AuNPs). Both Hg species trapped in the sorbents precipitates were quantified by electrothermal Atomic Absorption Spectroscopy (AAS) after direct injection in the graphite atomiser under optimal instrumental parameters (Ag and Au act as modifiers). The optimal solid-phase extraction conditions were examined and defined by batch method. Recoveries achieved by the developed analytical procedure were in the range 97-102% for both Hg(II) and methylmercury with limits of detection and quantification of 0.03 and 0.1 mu g L-1, respectively. The proposed analytical procedure was applied for speciation analysis of mercury in water samples.

Automated summary

A novel non-chromatographic approach for speciation analysis of mercury was developed using silver and gold nanocomposites as sorbents for solid phase extraction. Excellent separation and enrichment of Hg(II) and CH3Hg+ was achieved due to the specific behavior and affinity of the nanocomposite materials.