Bis-(4-hydroxypent-2-ylidene)-diaminoethane(BHPDE) is a Schiff base resulting from the condensation of pentane-2-,4 dione and 1,2-diaminoethane.Solid-phase Extraction of Ni (II) ion by column method in the pH range 1- 12 have been studied in trichloromethane using bis-(4-hydroxypent-2-ylidene)-diaminoethane(BHPDE). Ni (II) ion extraction using 2% BHPDE in CHCl₃is sufficient or abundant in the pH of 4.0. The aqueous BHPDE shows a maximum absorption at 320nm. The Ni (II) ion complex has maximum absorption at 375nm. The acid dissociation constants of H₂B (BHPDE) are obtained by titrating with 0.179 M NaOH and are found to be pka_1D = 11.55 and pka_2D = 11.5 corresponding to the formation of HB^- and B²respectively. Pka_1D and pka_2D share the same value since H₂B (BHPDE) has two protons located in the same chemical environment. Electronic Spectrum of BHPDE confirms that BHPDE absorbs maximally in the ultraviolet region of the spectrum and not in the visible region since it is not displayed in the spectrum. The physical modification of the silica gel using BHPDE has also been studied.

TABLE OF CONTENTS

Title page i

Certification page ii

Dedication page iii

Acknowledgement iv

Abstract v

Table of contents vi

CHAPTER ONE

1.0 Introduction 1

1.1 Background of the study 1

1.2 Objectives of the study 3

1.3 Statements of the problem 4

1.4 Hypothesis 5

1.5 Significance of the study 6

1.6 Limitation of the study 6

CHAPTER TWO

2.0 Literature review 7

2.1 Steps in solid phase- extraction 7

2.2 column and batch extraction method 10

2.3 Sorbent in solid- phase extraction 11

2.3.1 Silica gel 12

2.3.2 C18 - bonded silica gel 15

2.3.3 Aminopropyl silica gel 15

2.4 Metal ions under study 16

2.4.1 Nickel (II) ion 16

2.5 Pre-concentration of metal ions 17

2.5.1 Optimal pH 17

2.5.2 Exchange capacity SPE 18

2.6 Adsorption Isotherm 18

2.6.1 The Langmuir isotherm 20

2.6.2 Freundlich isotherm 20

2.7 Immobilized ligands in the solid-phase

Extraction 21

2.7.1 Chelation 21

2.7.2 Schiff’s bases 23

2.7.3 Salen 24

CHAPTER THREE

3.0 Materials and Method 26

3.1 Materials 26

3.1.1 Instruments/Equipment 26

3.1.2 Chemical reagents 28

3.2 Method 32

3.2.1 Synthesis of the Schiff’s base (BHPDE) 32

3.2.2 Activation of silica gel 33

3.2.3 Preparation of stock solution of the ligand (BHPDE) 34

3.2.4 Preparation of the buffer solutions

(PH1- pH 12) 35

3.2.5 Preparation of immobilized Schiff’s base

(BHPDE) silica gel 35

3.2.6 Preparation of the extraction column 36

3.2.7 Effect of sample volumes on coated or

Modified silica gel 36

3.2.8 Preparation of the standard calibration

Curve of the Ni (II) complex 38

3.2.9 Determination of the acid dissociation

Constant of the BHPDE 39 3.2.10 Determination of wavelength of maximum absorbance (â‹‹max) of aqueous BHPDE 39

CHAPTER FOUR

4.0 Result and Discussion 41

4.1 Results 41

4.1.1 Activation of silica gel 41

4.1.2 Properties of BHPDE 41

4.1.3 Electronic spectrum of BHPDE 42

4.1.4 Acid dissociation constants of BHPDE 43

4.1.5 Effect of sample volumes on modified

Silica gel 44

4.2 Discussion 46

4.2.1 Activation of silica gel 46

4.2.2 Properties of BHPDE 46

4.2.3 Electronic spectrum of BHPDE in

aqueous Solution 47

4.2.4 Acid dissociation constants of BHPDE 48

CHAds PTER FIVE

5. 0 Conclusion and Recommendation 49

5.1Conclusion 49

5.1.1 Recommendation 50

References 52

CHAPTER ONE

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 R₂C=NR^{1 (}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 Limitation 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.