Abstract: Dithioacetal derivatives with different para-substituents, X=H, CH3, OCH3, Cl and NO2 were synthesized and chemically immobilized on the surface of silica gel for the formation of five newly synthesized silica gel phases (I-V). Characterization of the silica gel surface modification by the organic compounds was accomplished by both the surface coverage determination as well as the infrared spectroscopic analysis. The metal sorption properties of the silica gel phases were studied to evaluate their performance toward metal-uptake, extraction and selective extraction processes of different metal ions from aqueous solutions based on examination of the various controlling factors. The studied and evaluated factors are the pH effect of metal ion solution on the metal capacity values (mmol g-1), equilibration shaking time on the percent extraction as well as the structure and substituent (X) effects on the determined mmol g-1 values. The results of these studies revealed a general rule of excellent affinity of these silica gel phases-immobilized-dithioacetal derivatives for selective extraction of mercury(II) in presence of other interfering metal ions giving rise to a range of 94-100% extraction of the spiked mercury(II) in the metal ions mixture. The potential application of the newly synthesized silica gel phases (I-V) for selective extraction of mercury(II) from two different natural water samples, namely sea and drinking tap water, spiked with 1.0 and 10.0 ng mL-1 mercury(II) were also studied by column technique followed by cold vapor atomic absorption analysis of the unretained mercury(II). The results indicated a good percent extraction and removal (90-100±3%) of the spiked mercury(II) by all the five silica gel phases. In addition, insignificant contribution by the matrix effect on the processes of selective solid phase extraction of mercury(II) from natural water samples was also evident.

Abstract: 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 (µmol 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.