Monolithic Silicas in Separation Science E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 592

Veröffentlichungsjahr: 2010

Beschreibung

Edited by the experts and pioneers in the field, this is the first monograph to cover the topic, containing the must-have information hitherto only scattered among journals.
Clearly divided into sections on preparation, characterization and modeling, and applications, this is essential reading for chemists, chromatographers, analytical chemists, biochemists and biologists.

Leseprobe

Table of Contents

Cover

Table of Contents

Half title page

Related Titles

Title page

Copyright page

Preface

List of Contributors

1 The Basic Idea and the Drivers

1.1 Definitions

1.2 Monoliths as Heterogeneous Catalysts

1.3 Monoliths in Chromatographic Separations

1.4 Conclusion and Perspectives

Part One: Preparation

2 Synthesis Concepts and Preparation of Silica Monoliths

2.1 Introduction

2.2 Background and Concepts

2.3 Synthesis of Silica Monoliths

2.4 Monolithic Columns Prepared in the Laboratory

2.5 Summary

3 Preparation and Properties of Various Types of Monolithic Silica Stationary Phases for Reversed-Phase, Hydrophilic Interaction, and Ion-Exchange Chromatography Based on Polymer-Coated Materials

3.1 Stationary Phases for Reversed-Phase Chromatography

3.2 Stationary Phases for Hydrophilic-Interaction Chromatography Separations

3.3 Stationary Phases for Ion-Exchange Separations

3.4 Advantages of Polymer-Coated Monolithic Silica Columns

Part Two: Characterization and Modeling

4 Characterization of the Pore Structure of Monolithic Silicas

4.1 Monolithic Silicas

4.2 General Aspects Describing Porous Materials

4.3 Characterization Methods of the Pore Structure of Monolithic Silicas

4.4 Comparison of the Silica Monolith Mesopore-Characterization Data

4.5 Comparison of the Silica Monolith Flow-Through Pore-Characterization Data

5 Microscopic Characterizations

5.1 Introduction

5.2 Preparation of Macroporous Silica Monolith

5.3 Laser Scanning Confocal Microscope Observation

5.4 Image Processing

5.5 Fundamental Parameters

5.6 Three-Dimensional Observation of Deformations in Confined Geometry

6 Modeling Chromatographic Band Broadening in Monolithic Columns

6.1 Introduction

6.2 The General Plate-Height Model

6.3 Use of the General Plate-Height Model to Predict Band Broadening in TSM Structures

6.4 Conclusion

Acknowledgments

Symbols

7 Comparison of the Performance of Particle-Packed and Monolithic Columns in High-Performance Liquid Chromatography

7.1 Introduction

7.2 Basic Columns Properties

7.3 Comparison of the Through-Pore Structures and Related Properties

7.4 Thermodynamic Properties

7.5 Kinetic Properties and Column Efficiency

7.6 Conclusions

Acknowledgments

Symbols

Part Three: Applications

8 Quantitative Structure–Retention Relationships in Studies of Monolithic Materials

8.1 Fundamentals of Quantitative Structure–Retention Relationships (QSRRs)

8.2 Quantitative Relationships between Analyte Hydrophobicity and Retention on Monolithic Columns

8.3 QSRR Based on Structural Descriptors from Calculation Chemistry

8.4 LSER on Monolithic Columns

8.5 Concluding Remarks

9 Performance of Silica Monoliths for Basic Compounds. Silanol Activity

9.1 Introduction

9.2 Reproducibility of Commercial Monoliths for Analysis of Bases

9.3 Activity of Monoliths towards Basic Solutes

9.4 Contribution of Overload to Peak Shapes of Basic Solutes

9.5 Van Deemter Plots for Commercial Monoliths

9.6 Performance of Hybrid Capillary Silica Monoliths for Basic Compounds

9.7 Conclusions

10 Quality Control of Drugs

10.1 Introduction

10.2 Analysis of Pharmaceutics

10.3 Natural Products Analysis

10.4 Analysis Speed and Performance

10.5 Method Transfer

10.6 Separation of Complex Mixtures

10.7 Monolith Derivatives and Versatile Application

10.8 Summary and Conclusions

11 Monolithic Stationary Phases for Fast Ion Chromatography

11.1 Fast Ion Chromatography

11.2 Historical Development of Fast Ion Chromatography

11.3 3 Advantages of the Bimodal Porous Structure of the Silica Monolith Matrix

11.4 Type and Properties of Silica Monolithic Columns Used in IC

11.5 Modification of Silica Monoliths for IC Separations

11.6 Operational Parameters

11.7 Analytical Applications

11.8 Future Work

Abbreviations

12 Monolithic Chiral Stationary Phases for Liquid-Phase Enantioseparation Techniques

12.1 Introduction

12.2 Organic Monolithic Materials for the Separation of Enantiomers

12.3 Silica-Based Monolithic Materials for the Separation of Enantiomers

12.4 Summary of the Present State-of-the-Art and Problems to be Solved in the Future

13 High-Speed and High-Efficiency Separations by Utilizing Monolithic Silica Capillary Columns

13.1 Introduction

13.2 Preparation of Monolithic Silica Capillary Columns

13.3 Properties of Monolithic Silica Capillary Columns

13.4 Monolithic Silica Capillary Columns for High-Efficiency Separations

13.5 Monolithic Silica Capillary Columns for High-Speed Separations

13.6 Future Considerations

13.7 Conclusion

14 Silica Monolithic Columns and Mass Spectrometry

14.1 Introduction

14.2 Offline Chromatography, LC MALDI MS

14.3 Online ESI LC/MS/MS for Proteomics and Selected Reaction Monitoring (SRM)

14.4 Online Reactors and Affinity Columns Coupled to Mass Spectrometry

14.5 Conclusion

15 Silica Monoliths for Small-Scale Purification of Drug-Discovery Compounds

15.1 Introduction

15.2 Instrumental and Operating Considerations

15.3 Preparative Separations and Sample Loading

15.4 Purification of Drug-Discovery Compounds

15.5 Conclusions

Acknowledgment

16 Monolithic Silica Columns in Multidimensional LC-MS for Proteomics and Peptidomics

16.1 Introduction

16.2 Liquid Chromatography as a Tool Box for Proteomics

16.3 Selectivity of Columns for MD-LC

16.4 Dimensions of Columns in MD-LC

16.5 Monolithic Silica Columns

16.6 Applications of Monolithic Silica in Proteomics – A Brief Survey

16.7 Summary and Conclusions

17 Silica Monoliths in Solid-Phase Extraction and Solid-Phase Microextraction

17.1 Introduction

17.2 Extraction Process

17.3 Extraction Platforms

17.4 Applications

17.5 Conclusion and Outlook

Index

Edited by

Klaus K. Unger, Nobuo Tanaka, and Egidijus Machtejevas

Monolithic Silicas in Separation Science

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The Editors

Prof. Klaus K. Unger

Am Alten Berg 40

64342 Seeheim-Jugenheim

Germany

Prof. Nobuo Tanaka

School Science & Technology

Kyoto Inst. of Technology

Matsugasaki, Sakyo-ku

Kyoto 606-8585

Japan

Dr. Egidijus Machtejevas

Merck KGaA

Perf. & Life Science Chemicals

Frankfurter Str. 250

64293 Darmstadt

Germany

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British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.d-nb.de.

© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

ISBN: 978-3-527-32575-7

ISBN: 978-3-527-63326-5(ebk)

Preface

One of the most prominent drivers in the field of separation science and technology is the search for novel and efficient materials as adsorbents to improve the mass transfer kinetics and to allow fast separations. While the major attention was directed to provide particle packed columns with smaller and smaller particles the idea to develop continuous beds based on silica monoliths was pioneered by Professor N. Soga and K. Nakanishi from Kyoto University, Japan, utilizing the template approach. It was a milestone in the development of silica monoliths when both researchers (NS and KN) had the splendid idea to introduce them as continuous beds in High Performance Liquid Chromatography (HPLC). In close collaboration with Professor K. Nakanishi, Dr Minakuchi and one of our co-editors (NT) performed the synthesis of such columns for HPLC. However, there was a serious limitation to apply monolithic silicas in 4 and 4.6 mm I.D. column format as the shrinkage of silica calling for a leak-tight and pressure stable cladding. This problem was finally solved by researchers (Dr K. Cabrera and Dr D. Lubda) from Merck KGaA, Darmstadt, Germany.

When my research group (KKU) became access to research samples from Merck, Darmstadt, at the mid of 1990s we were fascinated by the potential of silica monoliths as continuous beds in HPLC due to their flexibility in adjusting and controlling the morphology , pore structure and surface chemistry and thus enabling to optimize the chromatographic performance parameters. The second-generation monolithic silica columns just appearing seem to provide much higher performance than the first-generation columns commercialized in 2000.

The focus of Professor Tanaka’s group was the preparation and improvement of monolithic fused silica capillaries to generate high efficiency columns and to compare them with particle packed fused silica columns.

Professor Tanaka and Dr E. Machtejevas both could demonstrate the potential of such columns in various life science applications such as proteomics and peptidomics using multidimensional HPLC/MS.

After almost twenty years of extensive research and development in the field the three authors (KKU, NT and EM) became convinced that it is time to review the work under the various aspects of separation science.

The authors are jointly indebted to the division of performance and life science chemicals of Merck KGaA, Darmstadt, Germany, for the generous support and for supplying numerous micrographs of the material. The authors want to express their gratitude to the team of Wiley-VCH, Weinheim, Germany, in particular to Ms W. Wüst, for their excellent cooperation and assistance in editing the book. We would appreciate the comments of the readers for the improvement of a further edition.

Klaus K. Unger, Nobuo Tanaka and Egidijus Machtejevas

October 2010

List of Contributors

Abdelkarem Abed

Al-Azhar University-Gaza

Department of Pharmaceutical Chemistry

Gaza, P.O. Box 1277

Palestinian Territories

Cristina Anta

Centro de Investigación Lilly S.A.

Analytical Technologies Department

Avda. de la Industria 30

28108 Alcobendas, Madrid

Spain

Keith Ashman

Centro Nacional de Investigaciones Oncológicas (CNIO)

C/ Melchor Fernández Almagro, 3

28029 Madrid

Spain

Bezhan Chankvetadze

Tbilisi State University

School of Exact and Natural Sciences

Department of Physical and Analytical Chemistry and Molecular Recognition and Separation Science Laboratory

Chavchavadze Ave 3

0179 Tbilisi

Georgia

Gert Desmet

Vrije Universiteit Brussel

Department of Chemical Engineering

Pleinlaan 2

1050 Brussels

Belgium

Frederik Detobel

Vrije Universiteit Brussel

Department of Chemical Engineering

Pleinlaan 2

1050 Brussels

Belgium

Sami El Deeb

Al-Azhar University-Gaza

Department of Pharmaceutical Chemistry

Gaza, P.O. Box 1277

Palestinian Territories

Alfonso Espada

Centro de Investigación Lilly S.A.

Analytical Technologies Department

Avda. de la Industria 30

28108 Alcobendas, Madrid

Spain

Georges Guiochon

University of Tennessee

Department of Chemistry

Knoxville, TN 37996-1600

USA

Paul R. Haddad

University of Tasmania

School of Chemistry, Australian Centre for Research on Separation Science, School of Chemistry

Private Bag 75, Hobart

7001, Tasmania

Australia

Takeshi Hara

Justus Liebig University of Giessen

Department of Physical Chemistry

Heinrich Buff Ring 58

35392 Giessen

Germany

Tohru Ikegami

Kyoto Institute of Technology

Graduate School of Science and Technology

Department of Biomolecular Engineering

Gosho-Kaido-cho, Matsugasaki, Sakyo-ku

Kyoto 606-8585

Japan

Roman Kaliszan

Medical University of Gdask

Department of Biopharmaceutics and Pharmacodynamics

ul. Gen. J. Hallera 107

80-416 Gdask

Poland

Kazuyoshi Kanamori

Kyoto University

Graduate School of Science, Department of Chemistry

Kitashirakawa, Sakyo-ku

Kyoto 606-8502

Japan

Hian Kee Lee

National University of Singapore

Department of Chemistry

3 Science Drive 3

Singapore 117543

Singapore

Egidijus Machtejevas

Merck KGaA

Performance & Life Science Chemicals / Laboratory Business, Product Manager Analytical Chromatography

Frankfurter 250

64293 Darmstadt

Germany

Egl Machtejevien

Kaunas Medical University

Department of Obstetrics and Gynecology

Eiveni 2

50009 Kaunas

Lithuania

Satoshi Makino

Kyoto Institute of Technology

Matsugasaki, Sakyo-ku

Kyoto 606-8585

Japan

Michał J. Markuszewski

Medical University of Gdask

Department of Biopharmaceutics and Pharmacodynamics

ul. Gen. J. Hallera 107

80-416 Gdask

Poland

Nicolaus Copernicus University

Ludwik Rydygier Collegium Medicum, Department of Toxicology

ul. M. Skłodowskiej-Curie 9

85-094 Bydgoszcz

Poland

David V. McCalley

University of the West of England

Centre for Research in Biomedicine

Frenchay

Bristol BS16 1QY

UK

Shohei Miwa

Kyoto Institute of Technology

Matsugasaki, Sakyo-ku

Kyoto 606-8585

Japan

Kosuke Miyamoto

Kyoto Institute of Technology

Matsugasaki, Sakyo-ku

Kyoto 606-8585

Japan

Manuel Molina-Martín

Centro de Investigación Lilly S.A.

Analytical Technologies Department

Avda. de la Industria 30

28108 Alcobendas, Madrid

Spain

Kazuki Nakanishi

Kyoto University

Graduate School of Science, Department of Chemistry

Kitashirakawa, Sakyo-ku

Kyoto 606-8502

Japan

Pavel N. Nesterenko

University of Tasmania

School of Chemistry

Australian Centre for Research on Separation Science

School of Chemistry

Private Bag 75, Hobart

7001

Tasmania, Australia

Oscar Núñez

University of Barcelona

Department of Analytical Chemistry

Av. Diagonal, 647

08901 Barcelona

Spain

Masayoshi Ohira

GL Sciences, Inc.

237-2 Sayamagahara

Iruma 358-0032

Japan

Haruko Saito

Kyoto University

Graduate School of Science, Department of Chemistry

Kitashirakawa, Sakyo-ku

Kyoto 606-8502

Japan

Zhi-Guo Shi

National University of Singapore

Department of Chemistry

3 Science Drive 3

Singapore 117543

Singapore

Romas Skudas

Merck KGaA

PC-RLP-Polymer Materials

Frankfurter str. 250

64293 Darmstadt

Germany

Mohammed Taha

Al-Azhar University-Gaza

Department of Pharmaceutical Chemistry

Gaza, P.O. Box 1277

Palestinian Territories

Nobuo Tanaka

Kyoto Institute of Technology

Matsugasaki, Sakyo-ku

Kyoto 606-8585

GL Sciences, Inc.

237-2 Sayamagahara

Iruma 358-0032

Japan

Matthias Thommes

Quantachrome Instruments

1900 Corporate Drive

Boynton Beach, FL 33426

USA

Klaus K. Unger

Johannes Gutenberg University

Institut fuer Anorganische Chemie und Analytische Chemie

Duesberweg 10-14, DE-55099

Germany

Li Xu

National University of Singapore

Department of Chemistry

3 Science Drive 3

Singapore 117543

Singapore

1

The Basic Idea and the Drivers

Nobuo Tanaka and Klaus K. Unger

1.1 Definitions

The term “monolith” means a single stone and is used to describe a large stone of special origin. Ayer’s rock in the middle of Australia is such an object. A detailed description of the history of monoliths is given by Svec and Tennikova [1]. We would like to define a monolith in this chapter as a continuous porous object whose morphology and pore structure can be varied in a wide range. A monolith can be a foam, a ceramic piece, it can be made of a cross-linked polymer or composed of an oxide or even carbon. The morphology can change between a membrane, a thin disk, a cylindrical rod, and a ceramic carrier of substantial size. The pores range from millimeter size down to mesopores and micropores. Monoliths can have a broad monomodal distribution, a distinct bimodal distribution and even a trimodal distribution with a hierarchical order of the pores.

1.2 Monoliths as Heterogeneous Catalysts

The control of morphology and pore structure of monoliths has made them ideal support materials for specific heterogeneous catalysis in environmental applications where fast reactions take place at high temperatures. The catalytic reduction of exhaust of automobiles [2] and the removal of pollutants from stationary sources for example, the selective reduction of NOx, the removal of volatile organic compounds (VOC), the decomposition of NO and the oxidation of CO from exhaust gas [3] are typical examples.

For the first-mentioned application, a variety of ceramic monolithic supports are offered on the market that have mostly square channels and a honeycomb structure. The monoliths are made of cordierite and other high-temperature materials. They differ in the channel width and the thickness of channels. Generally, they are manufactured by extrusion from pastes that contain an oxide hydrate precursor and additives [4]. The shaped green bodies are dried and subjected to calcination. The monolith itself is nonporous. A porous layer at the channel surface is deposited through a wash-coat procedure by which a layer of finely divided oxide for example, gamma-alumina is formed. Catalytic compounds are precious metals such as platinum, palladium and rhodium that are deposited by a wet impregnation procedure. Typically, a monolithic catalyst has a loading of 2 to 5 g of precious metal per liter volume. Due to the complex composition of the components of the exhaust gas, the variation of gas velocity and reaction temperature, so-called three-way catalyst systems have been designed and developed [5].The catalytic converters for automobiles usually have an guaranteed average lifetime of 100 000 miles.

The monolithic catalysts for stationary sources for example, at power plants have much larger dimensions [3]. For instance, monoliths for selective catalytic reduction (=SCR catalysts) in NOx reduction have cells of 6 mm in diameter, a length of 1 meter and a wall thickness of 1 mm as shown in Figure 1.1. The advantages of such monoliths are: a low pressure drop, a low axial dispersion and a low radial heat flow.

Figure 1.1 View of a ceramic monolith DeNOx catalysts for reduction of nitrogen oxides at power plants

(By courtesy of Steuler Anlagenbau GmbH & Co, KG, Höhr-Grenzhausen, Germany).

1.3 Monoliths in Chromatographic Separations

The first materials to be used as continuous columns for gas and liquid chromatography were polyurethane foams [6–8]. However, the columns made offered a low column performance and exhibited a limited pressure stability.

Polymer-based monolithic materials were introduced by Hjerten et al. [9].

The pioneering work in the field of silica monoliths was made by Soga and Nakanishi [10, 11]. They combined the sol-gel chemistry of silica with a phase-separation mechanism of a system of slow dynamics resulting from the addition of hydrophilic polymers. The formation processes comprise a spinodal decomposition that produces a cocontinuous domain structure before fragmentation leading to a two-phase system. The transient cocontinuous domain structure was frozen by gelation to form the sponge-like morphology consisting of the silica hydrogel phase and the solvent phase. Interestingly, the morphology and pore structure of the resulting monolith can be changed over a wide range depending on the composition of tetramethoxysilane as the silica source, the solvent and the polymer in the phase diagram [12].

First, a cocontinuous monolith structure of silica skeletons and macropores in the size range between 1 and 10 µm is formed by a competitive process between a sol-gel transition and phase separation. A subsequent treatment of the monolith with an alkaline aqueous solution yielded mesoporous silica structures with a pore-size range of 5–30 nm. The macropores are termed as through-pores enabling a convective flow through the continuous column bed, while the mesopore (diffusional pores) are responsible for the selective separation by adsorption/desorption. It was the merit of the group in Kyoto to discover the potential and added value of silica monoliths for high-performance liquid chromatography (HPLC) [13].

When the monolithic silicas were manufactured as rods of 4 and 4.6 mm inner diameter, respectively, the task remained to clad the single pieces into leak-tight pressure-stable cylindrical columns with corresponding fittings. At the beginning the problem was solved by adapting the radial-compression column cartridge system developed by Waters where silica particles are filled in a plastic tube and the filled tube is then compressed by applying and maintaining an external pressure [13]. This device, however, was not a practical solution for monolithic silicas. Researchers from Merck KGaA, Darmstadt, solved the problem by a cladding process using poly(ether-ether-ketone) (PEEK) [14]. Monolithic silica columns are now commercially available as Chromoliths with varying column ID down to fused-silica capillaries. In the case of MonoClad columns available from GL Science, a silica monolith is covered by two layers of polymers and encased in a stainless steel tubing. This structure has higher pressure resistance than PEEK cladding [15]. It should be emphasized that the capillary silica monoliths do not require cladding as they are prepared in situ in fused-silica capillaries.

The major advantages of monolithic silica columns as compared to particle-packed columns were seen in the fast separation, short analysis time, and the low column pressure drop [16]. The first family of Chromolith columns of 4.6 mm ID exhibited a column performance comparable to a column packed with 3–4 µm particles and a pressure drop equivalent to those packed with 8–13 µm particles [17, 18]. The macropores of the Chromolith columns were approx. 2 µm and the mesopores approx. 12 nm. The surface functionality was an octadecyl bonding. Most of the applications were with low molecular weight analytes and with peptides.

In the years after the commercial introduction of the first monolithic columns, the direction for further development has become clear. Following the UPLC concept introduced by Waters [19], development work has focused on two areas:

1. Developing short monolithic silica columns capable of efficiencies up to 200 000 plates per meter and high-speed separations in a minute or less – performance parameters like a particulate column packed with sub-2-µm particles, but achieved with monolithic silica columns at much lower backpressure.

2. Developing monolithic columns producing 100 000 theoretical plates or more with a single column for high-resolution liquid chromatography without requiring very high operating pressures.

The primary quest is how can we optimize the design of a monolithic silica in order to achieve these goals.

Ultimately, the expectations led to research activities directed towards a better characterization of silica monoliths and to modeling and simulation studies correlating the properties of monoliths with the performance parameters in HPLC [20–22].

The primary questions were:

a) How can one characterize reliably the pore structure parameters, e.g., in monolithic silica capillaries?

b) Which pore structural parameters are relevant to improving the column performance and which values should be achieved?

c) Can one verify the proposed structures by a proper synthesis?

We are not yet in a position to answer these questions immediately.

However, substantial ground-breaking work in the named areas has been performed by Gzil [23], Grimes and Skudas [20, 22], Guiochon and coworkers [24, 25], and by Tallarek [18, 26].

In essence, the results and predictions need an experimental verification to develop much better materials. So far, column efficiency similar to that obtainable with 2.5 µm particles was reported [15, 27]. While the generation of 1 000 000 theoretical plates was shown to be possible with a silica monolith prepared in a capillary [28], the preparation of a homogeneous domain structure remains problematic. Moreover, the development of silica monoliths with regard to chromatographic selectivity by designing appropriate surface functionalities and their application to biopolymer separations is still in its infancy [29].

1.4 Conclusion and Perspectives

Monolithic silica columns, as compared to particle-packed columns, offer a number of advantages [30–32]:

1. Monolithic columns do not require a frit system, which is particularly advantageous in the case of a column in a fused-silica capillary.

2. Monolithic columns are robust and pressure stable and allow one to vary the flow rate in a wide range.

3. The pressure drop can be optimized as a function of the column performance by adjusting the pore structural parameters.

4. Silica monoliths can be designed according to the analyte targets: small-size pharmaceutical molecules, peptidic analytes and high molecular weight biopolymers.

5. Silica monolithic columns can be developed to provide a very large number of theoretical plates, e.g., more than 1 000 000, though accompanied by a long separation time, or a fast separation comparable with the performance of a particulate column packed with sub-2.5-µm particles.

Monolithic columns do have disadvantages with respect to their preparation:

1. Rod-type columns need cladding and this seems to be the biggest problem in column production. The cladding must be pressure-tight, but in addition may not disturb the flow or adsorption/desorption characteristics of the monolithic silica in the area where the monolithic silica is in contact with the cladding material.

2. Relatively large through-pores that contribute to a high permeability and low separation impedance may eventually limit the performance at high speed due to the large A-term contribution to the band broadening [25], unless monolithic silicas are prepared having very small-sized domains and high homogeneity.

Much work still has to be done to realize the expected performance of monolithic silica columns that can, at least in some aspects, exceed that of particulate columns and to achieve this with column formats suitable for practical applications.

References

1. Svec, F., and Tennikova, T.B. (2003) Historical Review in Monolithic Materials: Preparation, Properties and Applications (eds F. Svec, T.B. Tennikova, and Z. Deyl), Elsevier, Amsterdam, pp. 1–14.

2. Lox, E.S.J., and Engler, B.H. (1997) Environmental Catalysis – Mobile Sources in Handbook of Heterogeneous Catalysis, vol. 4 (eds G. Ertl, H. Knözinger, and J. Weitkamp), Wiley-VCH Verlag GmbH, Weinheim, pp. 1559–1633.

3. Janssen, F.J. (1997) Environmental Catalysis – Stationary Sources in Handbook of Heterogeneous Catalysis, vol. 4 (eds G. Ertl, H. Knözinger, and J. Weitkamp), Wiley-VCH Verlag GmbH, Weinheim, pp. 1633–1668.

4. Howitt, J.S. (1987) Advances in Automotive Catalysis Supports in Catalysis and Automotive Pollution Control (eds A. Crucq and A. Frennet), Elsevier, Amsterdam, pp. 301–313.

5. Weigert, W., and Koberstein, E. (1976) Autoabgasreinigung mit multifunktionellen Katalysatoren. Angew. Chem. Int. Ed. Engl., 88, 657–663.

6. Ross, W.D., and Jefferson, R.T. (1970) In situ-formed open-pore polyurethane as chromatography supports. J. Chromatogr. Sci., 8, 386–389.

7. Schnecko, H., and Bieber, O. (1971) Foam filled columns in gas chromatography. Chromatographia, 4, 109–112.

8. Lynn, T.R., Rushneck, D.R., and Cooper, A.R. (1974) High resolution-low pressure liquid chromatography. J. Chromatogr. Sci., 12, 76–79.

9. Svec, F., Tennikova, T.B., and Deyl, Z. (eds) (2003) Monolithic Materials: Preparation, Properties and Applications, Elsevier, Amsterdam.

10. Nakanishi, K., Motowaki, S., and Soga, N. (1992) Preparation of SiO2-TiO2 gels with controlled pore structure via sol-gel route. Bull. Inst. Chem. Res., 70 (2), 144–151.

11. Nakanishi, K. (1997) Pore structure control of silica gels based on phase separation. J. Porous Mater., 4, 67–112.

12. Nakanishi, K., Shikata, H., Ishizuka, N., Koheiya, N., and Soga, N. (2000) Tailoring mesopores in monolithic macroporous silica for HPLC. J. High Resolut. Chromatogr., 23, 106–110.

13. Minakuchi, H., Nakanishi, K., Soga, N., Ishizuka, N., and Tanaka, N. (1996) Octadecylsilylated porous silica rods as separation media for reversed-phase liquid chromatography. Anal. Chem., 68, 3498–3501.

14. Cabrera, K., Lubda, D., Eggenweiler, H.M., Minakuchi, H., and Nakanishi, K. (2000) A new monolithic-type HPLC column for fast separations. J. High Resolut. Chromatogr., 23, 93–99.

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