Spectrophotometric Detection of Free Mercury(II) Ions in Thimerosal and Aqueous Media Using8-Hydroxyquinoline Functionalized Gold Nanoparticles

Abstract A spectrophotometric method for determination of free Hg(II) ions in solutions of thimerosal and drinking water using AuNPs functionalized with 8-hydroxyquinoline (8HQ) is presented. The characterization of synthesized AuNPs was realized by UV/Vis spectra, SP-ICP-MS and TEM, with mean size of 21.2 ± 0.4 nm. The synthesized AuNPs were stable for about 65 days when protected from light and stored in polypropylene bottles under refrigeration at 4.0 ºC. Optimal conditions for colorimetric detection of Hg(II) were investigated, with the analytical wavelength being defined at 650 nm and ideal pH of the samples 7.0 ± 0.5. Over the concentration range 10 to 20 µmol L-1 detection of Hg(II) with the naked eye is possible due to the rapid color change of the medium from red to blue. However, for lower concentration ranges, between 0.5 to 5.0 µmol L-1, addition of 20 µL of 2.5 mol L-1 NaCl induces aggregation of nanoparticles, enhancing the detection limit to 0.1 µmol L-1. The selectivity of this approach was demonstrated in the presence of other metal ions. This fit-for-purpose sensor was successfully applied to the determination of free Hg(II) ions in thimerosal, a common preservative for vaccines, and has been adopted for use by Tecpar`s laboratory of the Parana Institute of Technology (Curitiba, Brazil).