1.0 Introduction
1.1 Background of the Study
Solid phase extraction (SPE) is a sample preparation technique by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties. Solid phase extraction has two phases which are stationary phase and mobile phase; the stationary phase is the silica gel while the mobile phase is nitric acid (Hennion and marie-claire, 1999).
Solid phase extraction uses the affinity of solutes dissolved or suspended in a liquid (known as the mobile phase) for a solid through which the sample is passed (known as the stationary phase) to separate a mixture into desired and undesired components. The result is that either the desired analytes of interest or undesired impurities in the sample are retained on the stationary phase. The portion that passes through the stationary phase is collected or discarded, depending on whether it contains the desired analytes or undesired impurities. If the portion retained on the stationary phase includes the desired analytes, they can then be removed from stationary phase for collection in an additional step, in which the stationary phase is rinsed with an appropriate eluent. Schiff base named after Hugo Schiff is a compound with the general structure R2 C=NR1 (R1?H) where R stands for a phenyl or alkyl group which makes the Schiff base a stable imine. This kind of ligands is able to coordinate metal ions through the imine nitrogen. Schiff base is normally applied to these compounds when they are being used as ligand to form coordinate complexes with metal ions. Its function is to increase the pre-concentration of the metal ions.
Solid phase extraction technique has several advantages over other pre-concentration methods in terms of reusability of the adsorbent, higher pre-concentration factor, lower consumption of reagents, ease of automation, its environmental friendliness, simplicity, economy. SPE technique is based on adsorption of the metal ion (nickel (II) ion) on silica gel coated with Bis (4-hydroxypent-2-ylidene)-diaminoethane (BHPDE) as a ligand (Taylor and Francis, 2000).
1.2 Objectives of the Study
The objective of this study is to activate and modify the silica gel and to develop the calibration curve of Schiff base.
- To be able to measure the quantity of a compound accurately, and to determine λ max of (BHPDE) ligand.
- To synthesize Schiff’ base which can be used as ligand in the solid support surface to get a new sorbent with high sorption or adsorption efficiency.
- To test the power of the prepared SG-extractor in pre-concentration of Ni (II) ions from aqueous solution.
- To optimize the conditions for extraction.
1.3 Statement of the problem
Different techniques are used for the separation and pre concentration of metal ions in the solution. Sample preparation techniques among which are liquid-liquid extraction, precipitation, Volatilization, ion-exchange mechanisms, etc are characterized by higher consumption of reagents, lower pre-concentration factor, inability to reuse adsorbent where obtainable, capital intensive and not environmentally friendly.
However, solid-phase extraction technique is the most popular sample preparation method which can be favored and advantageous in the area of its simplicity, ease to automation, lower consumption of reagents, economy, environmentally friendly and above all, high pre-concentration factor.
1.4 Hypothesis
Ho (Null hypothesis): Solid phase extraction of trace metals with the Schiff base Bis-(4-hydroxy pent-2-ylidene)-diaminoethane by column method.
Ha (alternate hypothesis): Solid phase extraction of trace metals without the Schiff base Bis-(4-hydroxypent-2-ylidene)-diaminoethane by column method.
1.5 Significance of the Study
In this study, Schiff base was synthesized which was used as a ligand in the solid phase support surface to get a new sorbent with high sorption efficiency.
Secondly, we were able to determine the concentration of some selected trace metals commonly found in our environment. This study may be useful to the young researchers who intend to investigate metal ions in our environment.
1.6 Limitations of the Study
This research work is limited to the use of solid particles silica gel to extract solute from liquid samples. It does not involve the study of gaseous samples that can be passing through the packed columns but rather only deals on liquid sample. This study uses Bis-(4-hydroxy pent-2-ylidene)diamino ethane as its Schiff base. The research also focuses only on one trace metal such as nickel (II) ion.
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