Methods for the Characterization of Electrostatic Interactions on Surface-confined Ionic Liquid Stationary Phases for High Pressure Liquid Chromatography PDF Download
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Author: Patrice Renée Fields
Publisher:
ISBN:
Category :
Languages : en
Pages : 211
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Book Description
This body of work is a continuation of work previously completed in our group that examines the retention properties of surface confined ionic liquid (SCIL) stationary phases under reversed-phase and supercritical fluid chromatographic conditions. SCIL's have been shown to be useful for separating a variety of both organic and inorganic compounds. However, there has been little work done to elucidate the different retention mechanisms and properties that allow for the wide range of retention modes observed. The first chapter provides a brief history and survey of the properties of ionic liquids. The first chapter also includes an overview of the linear solvation free energy relationship (LSER), which is used to characterize the retention of solute sets containing both neutral and ionizable compounds in under reversed-phase and supercritical conditions. This chapter also provides insight into the evolution and development of molecular solute descriptors. The second chapter discusses several methods that can be employed to modify the LSER model to account for electrostatic interactions between the SCIL stationary ohases and ionizable solutes in reversed-phase chromatography. The P, D and J solute descriptors are evaluated based on their ability to fit the retention of ionizable solutes to the LSER model and to produce coefficient values that are consistent with the underlying molecular interactions and what has been previously reported in reversed-phase studies. The third chapter investigates the use of the LSER model to characterize the retention mechanism of two SCIL stationary phases under supercritical conditions. The LSER coefficients generated via the multiple linear regression of chromatographic retention data are compared and analyzed for statistical difference from one another. The two SCIL phases are further compared to a 2-ethylpyridine (EP) stationary phase, which is more commonly used in chromatography with compressible fluids. This chapter further examines the viability of the P and J solute descriptors to describe the electrostatic interactions between the SCIL stationary phases and ionizable solutes under supercritical conditions. The fourth chapter examines the ion exchange properties of several SCIL stationary phases. A series of small inorganic ions in acetonitrile-water mixtures are used to probe mechanistic differences in the stationary phases due to the substituents attached to the exchange moiety after correcting for loading differences between the phases. Connections have been made between the observed retention properties and the solvation of both the anion analytes and the stationary phase. The fifth chapter summarizes the findings of the previous chapters and offers suggestions for the future directions for this project while the appendix describes a method for estimating the viscosity of binary and ternary supercritical fluids. The estimates are based on a form of Darcy's law and relates the effect of temperature, pressure and flow rate on the estimates.
Author: Patrice Renée Fields
Publisher:
ISBN:
Category :
Languages : en
Pages : 211
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Book Description
This body of work is a continuation of work previously completed in our group that examines the retention properties of surface confined ionic liquid (SCIL) stationary phases under reversed-phase and supercritical fluid chromatographic conditions. SCIL's have been shown to be useful for separating a variety of both organic and inorganic compounds. However, there has been little work done to elucidate the different retention mechanisms and properties that allow for the wide range of retention modes observed. The first chapter provides a brief history and survey of the properties of ionic liquids. The first chapter also includes an overview of the linear solvation free energy relationship (LSER), which is used to characterize the retention of solute sets containing both neutral and ionizable compounds in under reversed-phase and supercritical conditions. This chapter also provides insight into the evolution and development of molecular solute descriptors. The second chapter discusses several methods that can be employed to modify the LSER model to account for electrostatic interactions between the SCIL stationary ohases and ionizable solutes in reversed-phase chromatography. The P, D and J solute descriptors are evaluated based on their ability to fit the retention of ionizable solutes to the LSER model and to produce coefficient values that are consistent with the underlying molecular interactions and what has been previously reported in reversed-phase studies. The third chapter investigates the use of the LSER model to characterize the retention mechanism of two SCIL stationary phases under supercritical conditions. The LSER coefficients generated via the multiple linear regression of chromatographic retention data are compared and analyzed for statistical difference from one another. The two SCIL phases are further compared to a 2-ethylpyridine (EP) stationary phase, which is more commonly used in chromatography with compressible fluids. This chapter further examines the viability of the P and J solute descriptors to describe the electrostatic interactions between the SCIL stationary phases and ionizable solutes under supercritical conditions. The fourth chapter examines the ion exchange properties of several SCIL stationary phases. A series of small inorganic ions in acetonitrile-water mixtures are used to probe mechanistic differences in the stationary phases due to the substituents attached to the exchange moiety after correcting for loading differences between the phases. Connections have been made between the observed retention properties and the solvation of both the anion analytes and the stationary phase. The fifth chapter summarizes the findings of the previous chapters and offers suggestions for the future directions for this project while the appendix describes a method for estimating the viscosity of binary and ternary supercritical fluids. The estimates are based on a form of Darcy's law and relates the effect of temperature, pressure and flow rate on the estimates.
Author: David S. Van Meter (III.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 179
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Book Description
Author: Qian Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 196
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Book Description
The development of new chromatographic materials is a very active field within separation sciences providing improved efficiency for current separation methods and allowing the realization of new ones. The work presented in this dissertation focuses on the development of two new chromatographic materials: a stationary phase based on surface confined ionic liquids and hafnia support monolithic columns for chromatography. Silica particles were chemically modified with methoxysilane derivatives: 1-methyl-3-(trimethoxysilylpropyl)imidazolium bromide and 1-butyl-3-(trimethoxysilylpropyl)imidazolium bromide and used as the stationary phase for HPLC. The modified silica was characterized by thermogravimetric analysis (TGA) and NMR spectroscopy. The ionic liquid moiety was predominantly attached to the silica surface through two silanoxane bonds of the silane derivative. Columns packed with the modified silica material were tested under HPLC conditions. Evaluation of the stationary phase for HPLC was performed using aromatic carboxylic acids as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic interaction, and other electrostatic interactions. A monolithic column consists of a porous structure inside of a tube (or channel) that forms a continuous bed of chromatographic material. These type of columns present an alternative to packed columns due to their high permeability, absence of frits to confine the packing material, and ease of fabrication. The most common monoliths are based on silica support, polystyrene or polymethacrylate polymeric structures, or acrylamide gels. A new type of monolithic structures based on hafnium oxide (i.e., hafnia) was synthesized using a sol-gel process. The processing reactions and conditions were studied using different analytical methodologies (i.e., pH measurement, FTIR and NMR spectroscopy), in an effort to understand the critical parameters leading to the hafnia monolithic structure. This would allow control of the synthetic conditions to provide materials with desired physicochemical characteristics that can have an impact on chromatographic performance. To understand the sol-gel process in the solution phase, a 177 Hf NMR method was developed to conduct the study of the aqueous chemistry of Hf(IV); to the best of our knowledge, this is the first observation of the 177 Hf NMR signal. Characterization of the hafnia monolithic structure was also performed using TGA, fluorescence spectroscopy and XRD.
Author: 余銘恩
Publisher:
ISBN:
Category :
Languages : zh-CN
Pages :
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Author: Nasrin Syed
Publisher:
ISBN:
Category : High performance liquid chromatography
Languages : en
Pages : 92
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Book Description
High performance liquid chromatography is an important analytical technique used for the separation and identification of components in a mixture. The aim of this research project was to synthesize and characterize a silica hydride-based pentynoic acid stationary phase. Analytical techniques like elemental analysis and diffuse reflectance infrared fourier transform spectroscopy (DRIFT) were used to confirm the success of bonding between silica hydride and pentynoic acid moiety. The pentynoic acid Si-H column allows for retention of both polar and non-polar compounds by carefully selecting the concentration ratio of organic solvent to water in the mobile phase. The characterization of the column was done using a series of polar and nonpolar compounds by studying their aqueous normal-phase and reversed-phase chromatographic behavior. The interactions between the stationary phase and the analyte include both hydrophobic and ionic/electrostatic interactions. The effect of varying the pH of the mobile phase on retention time was examined. The column's ability to run under reverse and aqueous normal phase conditions provides unmatched versatility compared to type-B silica columns.
Author: Alain Berthod
Publisher: CRC Press
ISBN: 9780824799939
Category : Science
Languages : en
Pages : 636
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Book Description
Micellar Liquid Chromatography reviews the use of surfactant solutions at or above the critical micelle concentration as mobile phases in liquid chromatography. It employs a computer-assisted optimization methodology and integrates micellar liquid chromatography (MLC) with other chromatographic and electrophoretic techniques using surfactants. It also includes the MICHROM software package on CD-ROM to facilitate the application of equations and optimize efficiency of MLC systems.
Author: Antonia Perez De Los Rios
Publisher: Elsevier
ISBN: 044463262X
Category : Technology & Engineering
Languages : en
Pages : 379
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Book Description
Ionic Liquids in Separation Technology reports on the most important fundamental and technological advances in separation processes using ionic liquids. It brings together the latest developments in this fascinating field, supplements them with numerous practical tips, and thus provides those working in both research and industry with an indispensable source of information. The book covers fundamental topics of physical, thermal, and optical properties of ionic liquids, including green aspects. It then moves on to contexts and applications, including separation of proteins, reduction of environmental pollutants, separation of metal ions and organic compounds, use in electrochromic devices, and much more. For the specialist audience the book serves as a recompilation of the most important knowledge in this field, whereas for starting researchers in ionic liquid separation technology the book is a great introduction to the field. First book in the marketplace dedicated to ionic liquids in separation technology Contributions from scientists in academia and researchers in industry ensure the coverage of both scientific fundamentals and industrial applications Covers a broad collection of applications in separation technology which makes the book a single source of information Includes many practical tips for researchers in industry and scientists who apply ionic liquids in their work
Author: Zhuxu Wang
Publisher:
ISBN:
Category : Chemical bonds
Languages : en
Pages : 124
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Book Description
Author: Louis W. Yu
Publisher:
ISBN:
Category : Aldehydes
Languages : en
Pages : 450
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Book Description
Author: Rahul A. Patil
Publisher:
ISBN:
Category : Chemistry, Analytic
Languages : en
Pages : 222
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Book Description
Ionic liquids are popular in diverse scientific applications because of their unique physicochemical properties. The physicochemical properties of ionic liquids can be "tuned" by the modification of their structural moieties. Understanding of structure-property relationship is important if one wants to introduce a desired property in ionic liquid for a specific application. The initial part of this thesis will discuss the understanding of structure-property relationship of dicationic ionic liquids. Ionic liquids with high thermal stability are useful in many applications from simple solvents for high temperature reactions to high vacuum lubricants for space applications. This thesis presents the design, synthesis, and characterization of different thermally stable dicationic ionic liquids. ILs with TGA thermal stabilities in the range of 330 to 467 °C and inverse gas chromatography stabilities up to 400 °C are reported. The thesis also provides an understanding of the thermal behavior of ionic liquids at higher temperatures. The first, in depth thermal decomposition study of dicationic ionic liquids by using electrospray ionization mass spectrometer is presented, and it discusses the mechanism of thermal degradation of ionic liquids and their degradation products at high temperatures. Two important applications of thermally stable ionic liquids, stationary phases for gas chromatography and solvents for high temperature reactions are discussed in this thesis. Applications of thermally stable dicationic ionic liquid gas chromatography stationary phases for the high temperature separation of high molecular weight compounds is presented. Applications of ionic liquid stationary phases in the separation of structural isomers of toxic environmental pollutants, compounds with different functional groups and polarities are reported. A fundamental investigation of the effect of structural modifications such as cations, linkage chains, and anions on the selectivities of ionic liquids is discussed. The last chapter of the thesis presents the application of thermally stable monocationic phosphonium ionic liquid as a solvent in a high temperature synthesis. The advantages of higher thermal stability and the catalytic properties of ionic liquid were utilized for the "rapid" deprotection of tert-butoxy amino acids and peptides at higher temperatures.
