SOLID-PHASE EXTRACTION OF NICKEL (II) ION BY STUDYING THE EFFECTS OF SAMPLE VOLUME ON COATED SILICA GEL AND PRODUCTION OF SCHIFF’S BASE (BHPDE)

ABSTRACT

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 CHCl3 is 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 pka1D = 11.55 and pka2D = 11.5 corresponding to the formation of HB-   and B2 respectively. Pka1D and pka2D 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 (⋋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 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 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.

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