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Biotechnol. Prog. 1994, 10, 561-573
REVIEW ~~~~~
New Materials for Biotechnology: Chromatographic Stationary Phases Based on Zirconia Jacek Nawrocki Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznan, Poland
Christopher J. Dunlap and Peter W. Carr* Department of Chemistry, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455
John A. Blackwell? Analytical Development Laboratory, 3M Pharmaceuticals, 3M Company, 270-49-02, 3M Center, St. Paul, Minnesota 55144
This review explores the usefulness of zirconia-based materials in separations in biotechnology. The physical and chemical properties of zirconia are discussed briefly t o familiarize the reader with the advantages of zirconia. The use of native zirconia is then examined, with a study of the Lewis acidhase chemistry that defines chromatography with zirconia. Modification of the zirconia surface with small molecules is then discussed. Finally, polymer-coated zirconia materials are examined. Examples of separations using these various materials are shown. The advantages and disadvantages of each of these materials are presented.
Contents Introduction Physical Properties Chemical Properties Stability Surface Chemistry Gas-Solid Adsorption Chemistry Liquid-Solid Adsorption Chemistry Zirconia in Liquid Chromatography Chemical, Dynamic Modifications Low Molecular Weight Solute Retention Studies Protein Studies on Unmodified Zirconia Phosphated Zirconia Amnity Phases Immobilized Metal Ion Chromatography Chemical, Permanent Modifications Physically Screened Zirconia Particles Poly(butadiene)-CoatedZirconia Poly(ethy1ene imine)-Coated Zirconia Challenges for HPLC Zirconia Materials Conclusions
561 561 563 563 563 563 563 565 565 565 566 568 570 570 570 570 570 571 571 572
Introduction The purification of biomolecules is an important problem in biotechnology. One of the major methods used t Present address: DuPont-Merck Pharmaceuticals Chambers Works PRF-1, Deepwater, NJ 08023.
for this purification is chromatography. Unfortunately, many problems exist with current chromatographic supports. The ideal support would have a high surface area that is energetically homogeneous and that can be easily modified in a variety of ways. It would also be physically and chemically stable over a wide range of conditions (pH, solvent, temperature, etc.). Finally, it would be available in a wide range of particle and pore sizes. Current chromatographic supports are compared in Table 1. The focus of this review is on zirconium oxide, or zirconia. As can be seen from Table 1, zirconia has better mechanical strength than conventional polymer supports, while it is far more stable toward extremes in acidity and alkalinity than silica. Zirconia also has a unique surface chemistry that can be used for new and possibly more selective separations. These advantages have led to the investigation of zirconia as a chromatographic support. In this review, the physical and chemical properties of zirconia will be examined, followed by a look at the current state of chromatography using this material [for a more detailed examination of the physical and chemical properties of zirconia, see the review by Nawrocki et al. (1993)l.
Physical Properties Perhaps the most important factor in determining the physical properties of zirconia is its thermal history. Surface area, pore size and mechanical strength are all affected by the thermal history of the sample. Surface area, an important chromatographic characteristic, is very dependent on the thermal treatment of the material. Zirconia materials treated at temperatures above 500 "C will have a surface area below 100 mz/g (Nawrockiet al., 1993). Increasing the temperature will continue to decrease the surface area of the material. Chromatographic zirconia generally has a surface area in the 20-
8756-7938/94/3010-0561$04.50/0 0 1994 American Chemical Society and American Institute of Chemical Engineers
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Jacek Nawrocki received his M.S. (1972) and Ph.D. (1977) degrees from A. Mickiewicz University, Poznan, Poland. He was appointed head of the Department of Water Treatment Technology on the faculty of Chemistry at A. Mickiewicz University in 1991. His current research interests include the surface chemistry of silica and its use in chromatography.
Christopher J. Dunlap received his B.A. from Illinois Wesleyan University, Bloomington, IL, in 1990. He is currently pursuing his doctorate in analytical chemistry at the University of Minnesota under the direction of Professor Peter Carr, studying the coating of zirconia with hydrophilic polymers for use in chromatography.
John A. Blackwell received his bachelor’s degree in chemistry from the University of Minnesota in 1985. He then joined 3M in the Commercial Chemicals Division analytical laboratory. In 1991, he received his Ph.D. from the University of Minnesota working with Dr. Peter Carr on the ligand exchange properties of zirconia while on sabbatical from 3M. Dr. Blackwell is now a Senior Research Scientist in the Chemical Process R&D department of DuPont Merck Pharmaceutical Company. His research interests include novel supercritical mobile phases, adsorptive phenomena in condensed phases, and supercritical fluid technology.
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Peter W. Carr received his B.S. in chemistry (1965) from the Polytechnic Institute of Brooklyn and his Ph.D. from Pennsylvania State University (1969). In 1977, he joined the University of Minnesota, and he became a Professor of Chemistry in 1981. He helped found the Minnesota Chromatography Forum and served as its first president. Dr. Carr’s current research interests lie in the development of zirconia as a stationary phase material in high-performance liquid chromatography and the study of solvent- solute interactions as they pertain to the prediction of retention, selectivity, and optimization in chromatography.
30 m2/grange. This is a lower number than those of most chromatographic silicas. However, direct comparisons between silica and zirconia cannot be made on the basis of these numbers due to the large difference in the densities of zirconia (5.8 g/cm3)and silica (2.2 g/cm3).A better number to compare is m2/cm3 of bed volume. When this factor is taken into account, the surface areas of zirconia and silica are comparable. Pore size is also affected by thermal treatment. Materials treated a t temperatures below 500 “C contain a large fraction of micropores (
