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PHYSICAL MODIFICATION OF SILICA GEL

CHAPTER ONE

Physical Modification of Silica Gel with the Salen Bis(2,2́-Methylidenephenol)Diaminoethane and the Applications

INTRODUCTION

The use of salen-type tetradendate bis-schiff base ligands has found extensive applications in catalysis medicinal and biochemical fields and until recently, their use as analytical reagents was rarely reported (Nwabue and Okafor, 1992). Presently, the use of Schiff base for solid phase extraction has gained prominence as an analytical tool for preconcentration, trace metal ions determination and separation because of advantages in selectivity, sensitivity, efficiency of extraction, ease of determination of the analyte and as a green analytical method (Senevirantne and Cox. 2000). Also the use of silica gel as adsorbent especially immobilized with various organic compounds with metal chelating ability has received great attention (Kim and Yi. 1999). Most of the literature in this subject area concerns immobilization of the Schiff base on the surface of a solid support such as silica gel by chemical modification. So far not much has been reported on the use of physically modified silica gel with Schiff bases for adsorption and solid phase extraction of metal ions from solutions.

The pollution levels of the environment by heavy metals can be estimated by analyzing soil, water, and sediment and marine organisms after a prerequisite separation and/or pre-concentration steps. The removal and recovery of these metals have become very important because of their detrimental effects on our environment. Various treatment methods for the extraction of metal ions from aqueous solution have been in use, these include reduction, electrochemical precipitation, ion exchange, filtration, evaporation, solvent extraction, reverse osmosis, chemical precipitation, sedimentation, electro-dialysis, flocculation, neutralization, adsorption etc (Patterson, 1985; VoleSky et al. 1990). Most of these methods suffer from drawbacks such as high capital and operational cost or the disposal of residual metal sludge.

There is a strong need to provide chemical analysis more quickly and at low cost, and this implies that effort should be given to sample preparation portion of the analysis. This is aimed at reducing cost, providing more reproducible results, decreasing the use of organic solvent, providing cleaner extracts for instrumental measurements and time saving. These improvements are necessitated because greater portion of sample analysis time is spent in sample preparation. Also, most times, it is very important to determine the analytes in trace and ultra trace levels, for this purpose, there are a lot of highly sophisticated technologies that are fast, sensitive but expensive and complicated.

Although analytical chemists use some powerful techniques like atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), graphite carbon mass spectrometry (GC-MS), inductively coupled mass spectrometry (ICP-MS) flame atomic absorption spectrometry (FAAS) and graphite flame atomic absorption spectrometry (GFAAS), these techniques are combination of two techniques the sample preparation section and the detection tools (Janghan et al. 2005). These techniques are usually insufficient due to matrix interferences and the results obtained maybe erroneous if the limitations of these instrument are not observed because the metal ions may be present in these samples together with other elements. The high cost of these instruments is another factor that limits their use. The best course to obtaining reliable result is to separate and pre-concentrate the metal ions from the matrix constituents and then determine them in isolated state. Application of pre-concentration, results in the concentration of metal ion of interest while its separation from the matrix constituents results in the simplification of the sample matrix and immobilization of the metal ion in a more stable chemical form (Rakesh et al.2003).

Solid phase extraction (SPE), offers better option for the isolation and concentration of target analytes and the clean-up of samples. Combination of SPE with UV spectrophotometric method reaches the limit of detection of these high cost instruments. This gives opportunity to the small laboratories to increase their efficiency since solid phase extraction is cheap and has a lot of advantages instead of having sophisticated instruments which are always expensive and need a lot of services and accessories.

Objective

 

The main purpose of this project work is to study the adsorptive characteristics of silica gel for physical modification with Salen bis(2,2́ -methylidenephenol)diaminoethane and the application of the modified solid phase for extractive separation, pre-concentration and spectrophotometric determination of trace metal ions.

Specific Objective

To optimize the conditions for physical modification of silica gel with Salen bis(2,2́-methylidenephenol)diaminoethane (BMPDE).

To use the Salen BMPDE for physical modification of activated silica gel.

To optimize the conditions for metal ion extraction using the physically modified silica gel.

To study the effects of possible interferences on metal ion extraction using the modified solid phase.

To use the modified solid phase for pre-concentration and spectrophotometric determination of the metal ions.

To apply the developed procedure for analysis trace metals in real sample water. 

Statement of the Problem

Up till the time of this work, only few other works have been reported on the physical modification of silica gel with bis(2,2́-methylidenephenol)diaminoethane and the application of the modified sorbent for extractive separation and spectrophotometric determination of trace metal ions in aqueous samples. This work will therefore study the physical modification of silica gel with the Salen bis(2,2́-methylidenephenol)diaminoethane and the application of the physically modified solid phase for extractive separation and spectrophotometric determination of trace metal ions.  

 

There are several reports on the use of Schiff’s base metal complexes as catalyst in various organic syntheses and in biochemistry for elucidation of the structures of giant molecules such as proteins and DNA (Jacobsen et al. 1991). Few works have however appeared on the application of Salen type Schiff’s bases as reagents for solvent extraction and for physical adsorption on silica gel for spectrophotometric determination of trace metal ions.

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Physical Modification of Silica Gel with the Salen Bis(2,2́-Methylidenephenol)Diaminoethane and the Applications

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