Thiol-Functionalized Silica Thin Film Modified Electrode in Determination of Mercury Ions in Natural Water

The use of a thin thiol-functionalized silica film modified glassy carbon electrode in the determination of Hg(II) ions in a natural water sample is described. A typical measurement involves two successive steps: a glassy carbon electrode coated with a thin mesoporous silica film containing 10% of mercaptopropyl groups, according to the MPTMS/TEOS ratio in the starting sol-gel, was first immersed into the accumulation medium for 15 min, then removed, and finally transferred into a detection solution containing KCl 1.0 mol L-1 where detection was performed by anodic stripping voltammetry. In this medium the previously accumulated Hg2+ species complexed by the thiol groups in an open circuit preconcentration step is then directly reduced at -0.6 V during 60 s prior to be quantified by a differential pulse anodic scan from -0.6 to 0.3 V (vs. Ag/AgCl). A stripping peak appeared at about -0.01 V, which is directly proportional to the quantity of the analyte previously accumulated into the film. The best results were obtained under the following conditions: 100 mV pulse amplitude and 10 mV s(-1) scan rate in 1.0 mol L-1 KCl solution pH 2.0. Using such parameters a linear dynamic range from 1.00 to 10.0 x 10(-8) mol L-1 Hg(II) was observed with a limit of detection of 4.3 nmol L-1 for an accumulation time of 15 min. Hg(II) spiked in a natural water sample was determined between 97.0 and 101.4% mean recovery at 10(-8) mol L-1 level. The results indicate that this electrode is sensitive and selective for the Hg(II)determination.