SPECTROPHOTOMETRIC DETERMINATION OF CHROMIUM(III) AND CHROMIUM(VI) USING 2-[E)-[{3-[(2-HYDROXYBENZYLIDENE) AMINO]PHENYL}IMINO)METHYL]PHENOL

ABSTRACT

The Schiff base ligand, 2-[(E)-[{3–[(2-hydroxybenzylidene)amino]phenyl}imino)methyl]phenol was synthesized by condensing 1,3-diaminobenzene and 2-hydroxybenzaldehyde in absolute ethanol. Its Cr(III) and Cr(VI) complexes were equally synthesized. The ligand was characterized via UV, IR and NMR spectroscopy, whereas the complexes were characterized based on UV and IR spectroscopy and conductivity values. Stoichiometric studies indicated 1:1 metal to ligand ratio for both complexes. Cr(III) complex absorbed at 1042.56 cm^-1 υ(C-O), 532.37 cm^-1 υ(Cr-N) and 607.60 cm^-1 υ(Cr-O) while the Cr(VI) complex absorbed at 1182 cm^-1 υ(C-O), 749.37 cm^-1 υ(Cr-O) and 457 cm^-1 for υ(Cr-N).  Based on UV, IR and NMR studies, the ligand coordinated to the metals using the nitrogen and oxygen atoms. Spectrophotometric determination of the metals using the ligand was done at 368 nm for Cr(III)  and 465 nm  for Cr(VI).Optimum conditions for complexation and stability were studied and it was shown that optimum pH for Cr(III) and Cr(VI) were 13.0 and 2.0 respectively. Very few ions such as Co²⁺, Cu²⁺, Mn²⁺, Mg²⁺, Fe³⁺ and Zn²⁺ interfered with the determination. Beer’s law was obeyed between 0.02 to 0.14ppm for both metals. The method was successfully applied in the analysis of steel.

TABLE OF CONTENTS

Title page        –               –           –           –           –           –           –             i

Approval     –                 –           –           –           –           –           –           –           ii

Declaration              –           –           –           –           –           –           –           iii

Dedication      –           –        –           –           –           –           –           –           iv       Acknowledgements           –           –           –           –           –           –           –           v

Abstract             –           –           –           –           –           –           –           –           vi

Table of contents             –           –           –           –           –           –           vii

List of Tables  —           –           –           –           –           –           –           –           xi

List of Figures –      –           –           –           –           –           –           –           xii

List of Schemes          –           –           –           –           –           –           –          xiii

CHAPTER ONE

1.0   INTRODUCTION        –           –           –           –           –           –           1

1.1   Spectrophotometry        –           –           –           –           –           –           1

1.1.1    Beer- lambert’s law     –    –           –           –           –           2         

1.2       Schiff Base Ligands   –     –           –           –           –           –           4

1.2.1   Preparation of Schiff bases      –           –           –           –           –           4

1.2.2   Uses of Schiff Bases    –      –           –           –           –           –           6

1.2.3   Biological Importance of Schiff Bases                –           –           7

1.2.4    Schiff Base Metal Complexes              –           –           –           –           8

1.3     Chromium         –            –           –           –           –           –          

1.3.1   Determination of Chromium    –     –           –           –           –           9

1.3.2   Uses     –        –           –           –           –           –           –           10

1.4       Statement of the Problem      –           –           –           –           11       

1.5       Aims and Objectives                –           –           –           –           12

CHAPTER TWO

2.0 LITERATURE REVIEW     –           –           –           –           –           –           14

2.1   Catalytic Spectrophotometric Determination of Chromium   –           –           14

2.2  Spectrophotometric Determination Of Trace Level Chromium Using Bis

       (Salicylaldehyde) OrthophenyleneDiamine In Non-ionic Micellar Media          –           14  

2.3  Spectrophotometric Determination of Chromium(III) and chromium(VI)

       in sea water.-         –           –           –           –           –           –           –           15

2.4   Determination of Hexavalent Chromium in drinking water by ion chromatography        with post-column derivatization and UV-visible spectroscopic detection.         –           15                                  

2.5   Determination of Cr(VI) in environmental sample evaluating Cr(VI)          impact in a contaminated area.  –    –           –           –           16                                                                                                

    2.6   Indirect Extraction – Spectrophotometric Determination of chromium.            –           –           17

2.7   Sensitivity Determination of Hexavalent chromium in drinking water  –           –           18

2.8  Determination of Dissolved Hexavalent Chromium in Drinking Water, Ground Water        and Industrial Waste Water Effluents by Ion Chromatography-            –           –           –           18

CHAPTER THREE

3.0   Experimental                –           –           –           –           –           –           19

3.1   Apparatus         –           –           –           –           –           –           –           19

3.2   Preparation of Stock Solution     –   –           –           –           –           –           19

3.3    Preparation of Buffer Solutions –         –           –           –           –           20

3.4   Synthesis of the Ligand (HBAPP)      –           –           –           –           20

3.5  Synthesis of Chromium (III) and Chromium (VI)  Complexes of HBAPP        –            21

3.5.1 Determination of the Stoichiometry of the Complexes by Slope-Ratio Method.         22

3.6  General Procedure for the Complexation Studies         –           –           23

3.6.1 Effect of Time on the Formation of the Complexes      –           –           23

3.6.2 Effect of Temperature on the Formation of the Complexes   –           23

3.6.3 Effect of Concentration of Reagent on the Formation of the Complexes        –           23

3.6.4 Effect of pH on the Formation of the Complexes     –           –          23

3.6.5 Effect of Interfering Ions on the Formation of the Complexes            –           –           –           23

3.6.6 Calibration Curve-Beer’s Law   –          –           –           –           –           24

3.7  Determination of Chromium in Alloy               –           –           –           24

3.7.1  Determination of Chromium in Alloy with Flame Atomic Absorption

       Spectrophotometry          –         –           –           –           –           –           24

3.7.2 Determination of Chromium in Alloys with UV Spectrophotometry   –           –           24

CHAPTER FOUR

4.0     Results And Discussion             –           –           –           –           26

4.1       Physical Characterization and Molar Conductivity Data of the Ligands and Its    Cr(III) and Cr(VI) Complexes   –           –           –           26

4.2     Spectroscopic Characterization Of The Ligand And Its Cr(III) And Cr(VI)     Complexes.       –           –           –           –           –           –           –           26

4.2.1    Electronic Spectral Data of the Ligand and Its Complexes –           26

4.2.2   Infrared Spectra               –           –           –           –           –           27

4.2.3  ¹H and ¹³C NMR Spectra of the Ligand              –           –           –           28

4.2.4   ¹³C NMR          –             –           –           –           –           –           29

4.2.5   APT (Attached Proton Test)    –       –           –           –           –           29

4.3     Stiochiomery of the Complexes      –           –           –           –           30

4.3.1    Metal-Ligand Mole Ratio of Cr(III) Complex      –           –           30

4.3.2    Metal-Ligand Mole Ratio of Cr(VI) Complex       –           –           31

4.3.3   Molecular Formulae and Structures of the Ligand and Its Complexes           –           33

 4.4      Complexation Studies –       –           –           –           –           –           35

4.4.1   Effect of Time on the formation of the Complexes    –           –           35

4.4.2  Effect of the concentration of the reagent on the formation of the complexes           –           36

4.4.3  Effect of temperature on the formation of the complexes    38

4.4.4  Effect of pH on the absorbance of the complexes     –           –           41

4.4.5  Effect of interfering ions on the formation of Cr(III) and Cr(VI) complexes –           42

4.5     Calibration curve for determination of Cr(III) and Cr(VI) complexes            –           44

4.5.1  Cr(III) complex –               –           –           –           –           –            44

4.5.2  Cr(VI) complex –                    –           –           –           –           –           45

4.6    Application using steel solution –               –           –           –           –           46

4.6.1 Determination of Cr(III) in the steel solution    –         –           –           47

4.6.2 Determination of Cr(VI) in steel solution          –           –           –           47

4.7 Conclusion            –              –           –           –           –           –           47

4.8 Recommendation  –                   –           –           –           –           –           48

References      –           –                   –           –           –           –           –           49

Appendix A    –           –    –           –           –           –           –           –           55

Appendix B    –           –         –           –           –           –           –           –           58

LIST OF TABLES

3.1: Preparation of Buffer Solution    –           –           –           –           –           21

4.1: Physical Data of the Ligands and Its Complexes         –           –           26

4.2: Electronic Spectra            –   –           –           –           –           –           –           27

4.3: Infrared Spectral Data of the Ligand and Its Complexes   –      –           28

4.4: ¹HNMR Spectral of the Ligand in CDCl₃ relative to TMS (ppm)          –           –           28

4.5: 13CNMR Spectral Data of the Ligand   –         –           –           –           29

4.6. Effect of some interfering ions on Cr(III) Complex    –           –           43

4.7  Effect of some interfering ions on Cr(VI) complex     –           –           44

4.8. Determination of Cr(III) in the steel solution-         –           47

4.9. Determination of Cr(VI) in the steel solution-            –           –           47

4.10. Result of slope-Ratio plot for Cr(III) complex-fixed ligand(1.0X 10-3  M)                 55       

4.11. Result of Slope- Ratio plot for Cr(III) complex- fixed metal (1.0 X10-3 M)               55       

4.12. Result of Slope-Ratio plot for Cr(VI) complex; fixed ligand (1.0 X 10-3 M)              55

4.13. Result of Slope- Ratio plot for Cr (VI) complex; fixed metal (1.0 X-3M)                   56

4.14.Variation of Absorbance With Time for the Formation of the Complexes                    56

4.15.Variation of Absorbance with Reagent Concentration for the Formation of   Complexes.           –     –           –           –           –           –           –           56       

4.16.Variation of Absorbance with Temperature for the Formation of the        Complexes.          –           –                  –           –           –           –           57

4.17. Variation of Absorbance with pH for the Formation of the Complexes.          –           57

4.18   Results of Calibration Curve-Beer’s Law for Cr(III) and Cr (VI) Complexes                        57       

LIST OF FIGURES

4.5: Effect of Time on the formation of Cr(III)complex     – – 35

4.6: Effect of Time on the formation of Cr(VI)complex          –           –           36

4.7: Effect of concentration on the formation of Cr(III) complex                 –           –           37

4.8: Effect of concentration on the formation of Cr(VI) complex                 –           –           38

4.9: Effect of Temperature on the formation of Cr(III)complex   39

4.10: Effect of Temperature on the formation of Cr(VI)complex    –           40

4.11: Effect of pH on the formation of Cr(III)Complex          –           –           41

4.12: Effect of pH on the formation of Cr(VI) Complex         –           –           42

4.13 Calibration curve of Cr(III) complex             –           –           –           45

4.14 Calibration Curve of Cr(VI) Complex   –           –           –           –           46

LIST OF SCHEMES

1  Formation of Schiff  base   –          –           –           –           –           –           22

 2  The ligand  –         –           –           –           –           –           –           –           33

 3 Chromium(III) complex          –           –           –           –           –           –           34

 4  Chromium(VI) complex     —           –           –           –           –           –           34

CHAPTER ONE

INTRODUCTION

1.1  SPECTROPHOTOMETRY

            Spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength¹. It is more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near-ultraviolet, and near-infrared, but does not cover time-resolved spectroscopic techniques. Spectrophotometry is a very fast and convenient method of qualitative analysis, due to the fact that absorption occurs in less than one second and can be measured very rapidly. Molecular absorption is valuable for identifying functional groups in a molecule and for the quantitative determination of compounds containing absorbing groups^2,3. A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass or gases. However, they can also be designed to measure the diffusivity of any of the listed light ranges that usually cover around 200 – 250 nm using different controls and calibrations¹ .

            The most common spectrophotometers are used in the UV and visible regions of the spectrum and some of these instruments also operate into the near-infrared region as well. Visible region (400 – 700 nm) spectrophotometry is used extensively in colorimetry science. Ink manufacturers, printing companies, textile, vendors and many more, need the data provided through colorimetry. They take readings in the region of every 5 – 20 nanometers along the visible region and produce a spectral reflectance curve or a data stream for alternative presentations.

            Spectrophotometeric method is undoubtedly the most accurate method for determining, among other things, the concentration of substances in solution, but the instruments are of necessity more expensive. A spectrophotometer may be regarded as a refined filter photoelectric photometer which permits the use of continuously variable and more nearly monochromatic bands of light. The essential parts of a spectrophotometer are (1) a source of radiant energy (2) a monochromator i.e. a device for isolating monochromatic light or, more accurately, narrow bands of radiant energy from the light source (3) glass or silica cells for the solvent and for the solution under test and (4) a device to receive or measure the beams of radiant energy passing through the solvent⁴. 

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