Selective pre-concentration and solid phase extraction of mercury(II) from natural water by silica gel-loaded dithizone phases

Two silica gel phases loaded with dithizone were synthesized based on chemical binding and physical adsorption approaches. The stability of a chemically modified dithizone phase (I) was found to be more superior than that of a physically adsorbed one (II), especially in concentrated hydrochloric acid which was then used as a recycling and pre-concentration reagent for further uses of phase (I). The application of these two silica gel phases for sorption of a series of metal ions was performed by using different controlling factors such as the pH of metal ion solution and the equilibration shaking time by the static technique. For most metal ions, the determined metal capacity values (mu mol g(-1)) were found to be higher in the case of phase (I) as compared to phase (II). This difference was interpreted on the basis of selectivity incorporated in these sulfur containing silica gel phases. Hg(II) was found to exhibit the highest affinity towards extraction by these silica gel phases. The pronounced selectivity was also confirmed from the determined distribution coefficient (K-d) of all the metal ions, showing the highest value reported for mercury(II) to occur by phase (I). The potential applications of phase (I) for selective extraction of mercury(II) to occur from aqueous solution were successfully accomplished as well as pre-concentration of low concentration of Hg(II) (20 pg ml(-1)) from natural tap water with a pre-concentration factor of 200 for Hg(II) off-line analysis by cold vapor atomic absorption analysis. (C) 2000 Elsevier Science B.V. All rights reserved.