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New mixed-mode methacrylate-based polymeric monoliths prepared via complexation with cyclodextrins employed as stationary phases for capillary electrochromatography [Elektronische Ressource] / vorgelegt von Fuad Al-Rimawi

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New mixed-mode methacrylate-based polymeric monoliths prepared via complexation with cyclodextrins employed as stationary phases for capillary electrochromatography Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat) dem Fachbereich Chemie der Philipps-Universität Marburg Vorgelegt von Fuad Al-Rimawi aus Ramallah/Palästina Marburg/Lahn 2007 Die vorliegende Arbeit entstand in der Zeit von April 2004 bis Juli 2007 unter der Leitung von Prof. Dr. Ute Pyell am Fachbereich Chemie der Philipps-Universität Marburg. Vom Fachbereich Chemie der Philipps-Universität Marburg als Dissertation am 28. 06. 2007 angenommen Erstgutachter: Prof. Dr. Ute Pyell Zweitgutachter: Prof. Dr. Andreas Seubert Tag der mündlichen Prüfung am 23.07.2007 Gedruckt mit Unterstützung des Deutschen Akademischen Austauschdienstes II To my family, my Wife, My son (Yousef), To my Homeland Palestine III Acknowledgments I would like to thank Prof. Dr. Ute Pyell for her kind supervision, valuable guidance and her keen interest in my research project throughout my stay at her laboratory. Also I thank Prof. Dr. Andreas Seubert for fruitful discussions regarding my laboratory work. Thanks are also due to Dr. Uwe Linne for providing the μ-LC instrument, Dr.

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Published 01 January 2007
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New mixed-mode methacrylate-based polymeric monoliths
prepared via complexation with cyclodextrins employed as
stationary phases for capillary electrochromatography




Dissertation
zur
Erlangung des Doktorgrades
der Naturwissenschaften
(Dr. rer. nat)



dem
Fachbereich Chemie
der Philipps-Universität Marburg


Vorgelegt von
Fuad Al-Rimawi

aus
Ramallah/Palästina



Marburg/Lahn 2007












Die vorliegende Arbeit entstand in der Zeit von April 2004 bis Juli 2007 unter der Leitung
von Prof. Dr. Ute Pyell am Fachbereich Chemie der Philipps-Universität Marburg.





Vom Fachbereich Chemie der Philipps-Universität Marburg als Dissertation am 28. 06. 2007
angenommen








Erstgutachter: Prof. Dr. Ute Pyell
Zweitgutachter: Prof. Dr. Andreas Seubert




Tag der mündlichen Prüfung am 23.07.2007













Gedruckt mit Unterstützung des Deutschen Akademischen Austauschdienstes

II


























To my family, my Wife,
My son (Yousef),
To my Homeland
Palestine
















III
Acknowledgments
I would like to thank Prof. Dr. Ute Pyell for her kind supervision, valuable guidance and her
keen interest in my research project throughout my stay at her laboratory. Also I thank Prof.
Dr. Andreas Seubert for fruitful discussions regarding my laboratory work.
Thanks are also due to Dr. Uwe Linne for providing the μ-LC instrument, Dr. Andreas
Schaper for carrying out the SEM measurements, Frau Czerny for performing porosity
analysis. I also acknowledge Prof. Dr. Thomas Schrader and his research group for providing
the software for nonlinear regression calculations.
My thanks are extended also to my colleagues in AK Pyell (Carolin Huhn, Annika Wahl,
Barbara Hermann, Jan Rittgan, Susanne Dieckmann) and my colleagues at Philipps-
Universität Marburg (Sajid Malik from Biology department, Wael Derwish and Yasser
Elgamel from Chemistry department) for their cooperation and nice company. I thank also my
short-practical students Sebastian Kamps and Markus Rauber.
I am grateful to Deutscher Akademischer Austauschdienst (DAAD) for the financial support
throughout my stay in Germany.
I can not end without thanking my family for their encouragement and love throughout my
stay at Philipps-Unvirsität Marburg, Germany. This thesis is dedicated to them.


















IV
Table of Contents


List of abbreviations and symbols …………………………………………………...
11 Introduction and Objectives ….
32 Theoretical Background ……………………………………………………….
2.1 Capillary electrochromatography ……………………………………………... 3
2.2 Electrophoresis and electroosmosis …………………………………………... 4
2.3 Fundamentals of chromatography ……………………………………………. 7
2.4 Instrumentation ……………………………………………….. 12
2.5 Mobile phases for CEC ………………………… 13
2.6 Column technology …………………………………………… 13
2.6.1 Packed-bed columns …………………………………………………………. 14
2.6.2 Open tubular columns ………………………... 15
2.6.3 Monolithic stationary phases for CEC ……………………………………….. 15
2.6.4 Microchips …………………………………………………………………… 20
2.7 Host-guest complexation using cyclodextrins ………………………………... 20
233 Experimental ……………………………………………………………………..
3.1 Pre-treatment of the capillary ………………………………………………… 23
3.2 Synthesis of the monolithic stationary phases ………………………………... 23
3.3 CEC instrument ……………………………………………………………….. 26
3.4 Other instruments ……………………………………………………………... 28
3.5 Preparation of the mobile phase ………………………………………………. 28
V
3.6 Analytes used ………………………………………………………………... 29
324 Results and Discussion …………………………………………………………
4.1 Selection of the hydrophobic monomers ……………………………………. 32
4.2 Solubilization of the hydrophobic monomers by host-guest complexation … 33
4.3 Stoichiometry of the host-guest complexes …………………………………. 34
4.4 Selection of the best cyclodextrin as solubilizing agent …………………….. 36
4.5 Determination of complex formation constant ……………………………… 39
4.5.1 Capillary electromigration methods …………………………………………. 39
4.5.1.1 Cyclodextrin-modified MEKC ……………... 39
4.5.1.2 Cyclodextrin-modified CEC ………………………………………………... 41
4.5.2 Spectroscopic methods ……………………………………………………… 45
1 4.5.2.1 H NMR chemical shift analysis …………………………………………….. 45
1 4.5.2.2 H NOESY spectra …………………………………………………………... 51
4.6 Monolith synthesis ………….. 55
4.7 Variation of the content of hydrophobic monomer ………………………… 57
4.8 Variation of total monomer concentration ………………………………….. 61
4.8.1 Effect on the retention factors ………………………………………………. 61
4.8.2 Effect on permeability and electroosmotic mobility ………………………... 62
4.8.3 Effect on the porosity ……………………………………………………….. 65
4.9 Porosity analysis of the monoliths ………….. 66
4.10 Scanning Electron microscopy ……………………………………………... 69
VI
4.11 Chromatographic properties of the monoliths ……………………………... 71
4.11.1 Efficiency (Van Deemter plots) …………………………… 71
4.11.2 Selectivity for noncharged analytes ……………………….. 74
4.11.2.1 Aqueous mobile phase ……………………………………………………. 74
4.11.2.2 Nonaqueous mobile phase ………………………………………………… 79
4.11.3 Comparison of CEC-monoliths with LC-columns packed with C18-silica gel …. 80
4.11.4 Comparison of the separation on monoliths using CEC and µ-LC ……….. 83
4.11.5 Selectivity of weak electrolytes …………………………………………… 85
4.11.5.1 Determination of corrected retention factors ……………… 86
4.11.5.2 Separation of charged analytes …………………………………………… 88
4.11.6 Comparison of separation selectivity obtained by CEC and by CE ………. 100
4.12 Investigation of the retention mechanism of charged analytes ……………. 103
4.12.1 Effect of counter ion concentration ……………………………………….. 104
4.12.2 Effect of vinylsulfonic acid concentration ………………… 106
4.12.3 Effect of isobornyl methacrylate concentration …………… 109
4.13 Investigation of the quantitative relationship between solvophobic and 112
ion-exchange interactions …………………………………………………
4.14 Reproducibility and stability of the monolithic capillaries ………………... 123
1265 Conclusions ……………………………………………………………………….
1276 References …………………………
1347 Summary …………………………………………………………………………..
1378 Summary in German (Zusammenfassung) ……………………………....
1409 Appendices ………………………………………………………………………..

VII
List of abbreviations and symbols

A Coefficient of eddy diffusion
AMPS 2-acrylamido-2-methyl-1-propanesulfonic acid
APS Ammonium persulfate
AS Ammonium sulfate
B Coefficient of longitudinal diffusion or complex formation constant
B Complex dissociation constant D
C Dodecyl methacrylate 12
C Octadecyl methacrylate 18
C Cyclohexyl methacrylate 6
c Molar concentration of free solute in the mobile phase aq
c Molar cof complexed solute in the mobile phase com
CD Cyclodextrin
CE Capillary electrophoresis
CEC Capillary electrochromatography
c Molar concentration of an analyte in the mobile phase m
C Coefficient of the resistance to mass transfer in the mobile phase m
CMC Critical micellar concentration
c Molar concentration of free solute in the stationary phase s
C Coefficient of the resistance to mass transfer in the stationary phase s
%C Crosslinker concentration
d Capillary diameter
DMAA N,N-dimethylacrylamide
DMF Dimethylformamide
E Applied electric field
VIII
EOF Electroosmotic Flow
F Volume flow rate
F Faraday constant k
FT-IR Fourierr Transform Infrared Spectroscopy
H Plate height
HEMA 2-hydroxyethyl methacrylate
HPLC High performance liquid chromatography
1H NMR Nuclear magnetic resonance
1H NOESY Nuclear Overhauser Enhancement Spectroscopy
I Ionic strength
I.D. Inner diameter
ISEC Inverse size-exclusion chromatography
K Partitioning coefficient
K Permeability p
k Retention factor
k Apparent retention factor app
k Corrected retention factor c
k Observed retention factor obs
K Distribution coefficient distr
oK Specific permeability
L Length of a separation bed
LC Liquid chromatography
L Effective length of a capillary eff
L Total length of a capillary tot
MA Methylacrylamide
MEKC Micellar electrokinetic chromatography
IX
N Plate number
n Methylene selectivity CH2
O.D. Outer diameter
OT-CEC Open-tubular electrochromatography
PDA Piperazinediacrylamide
pH* Apparent pH
pI Isoelectric point
q Charge
r Radius
R Gas constant or resolution
ROESY Rotating frame Overhauser Effect Spectroscopy
2S Variance
SDS Sodium Dodecyl Sulfate
SEM Scanning electron microscopy
T Temperature
t Hold-up time0
TEM Transmission electron microscopy
TEMED Tetramethylethylenediamine
THF Tetrahydrofuran
t Retention timeR
%T Total monomer concentration
U Applied voltage
u Linear velocity
UV Ultraviolet
v Migration velocity
v Linear velocity of electroosmotic flow eo
X