Comparison of metal sorption properties of three silica gel phases - Physically adsorbed and chemically immobilized-1-aminoanthraquinone

I-Aminoanthraquinone was used for the modification of a silica surface by chemical reaction procedure as well as physical adsorption approach. Two different silica gel phases were synthesized on the basis of chemical binding of either nitrogen or oxygen atom of the organic modifier and one silica gel phase was formed upon physical adsorption of I-aminoanthraquinone on the surface of silica gel. The stability test of the three newly synthesized silica gel phases (I-III) was performed in different buffer solutions (pH 1-6) for evaluation of the leaching process as well as identification of the most suitable buffer range for the analytical applications of phases (I-III). The physically adsorbed silica gel phase (I) was found to exhibit maximum hydrolysis percentage values while phases (II) and (III) were found to be fairly resistant to hydrolysis. The experimental buffer range for application of each phase was also stated on such phase hydrolysis. Applications of phases (I-III) for metal sorption processes of thirteen different metal ions were studied in an attempt to compare and evaluate the different trends of chemically and physically modified silica gel phases toward metal extraction in different controlling factors such as pH and equilibration time. The results of these studies indicate that phase (III) is the best in metal extraction and binding of most tested metal ions and the lowest is phase (I). The determined order for the metal exchange capacity (mmol g(-1)) for the tested metal ions by phases (II) and (III) are very similar in many respects but phase (I) was found to be quite different. More aspects of the comparison of the physically adsorbed and chemically immobilized silica gel phases were also reported. The potential applications of chemically modified silica gel phases (II, III) as selective solid phase extractors and pre-concentrators for Cu(II) and Cr(III) (similar to 1.0 mug mL(-1) and similar to 1.0 mug mL(-1)) from natural sea water samples were also performed to study and evaluate the matrix effects. The results of this study proved good percentage extraction values of 98.5-96.3 +/- 2.0-3.0% for these tested metal ions by the two silica gel phases (II, III). The pre-concentration percentage recovery values for the tested metal ions were found to be in the range of 96.8-94.2 +/- 3.0-6.0 % by the two newly modified silica gel phases (II, III) without any noticeable matrix effect and satisfying a preconcentration factor of 500.