Stationary phases zirconia-based

Hu, Y. and Carr, P. W., Synthesis and characterization of new zirconia-based polymeric cation-exchange stationary phases for high-performance liquid chromatography, Anal. Chem., 70, 1934, 1996. 

Despite the problems with silica, it has remained dominant as a stationary phase for the analysis of bases for the same reasons as it has for the separation of other classes of solute. Polymeric phases still give lower efficiency than silica phases, and at low pH seem to suffer the same overloading effect as silica-based phases. lonogenic groups seem to be introduced into polystyrene-divinyl-based phases during their manufacture, and these can lead to tailing of bases at intermediate pH where these groups become ionized. Other phases, such as those made from zirconia, show some promise for the analysis of bases but have not been fully evaluated as yet. 

C is not recommended and high-temperature LC has not been rigorously explored. With the advent of thermally stable phases such as zir-conia-based stationary phases, temperatures in excess of 150°C can now be utilized. Many zirconia-based phases are available, so the stability of stationary phases is less of an issue. 

Column temperature affects the relative retention of different compounds and elevated temperature permits high-speed chromatography to be conducted.25 Figure 25-28 suggests a systematic procedure for method development in which solvent composition and temperature are the two independent variables.1 For elevated temperature operation, pH should be below 6 to retard dissolution of silica. Alternatively, zirconia-based stationary phases work up to at least 200°C. 

Another porous base material suggested in the last decade as an alternative to silica is zirconia. Zirconia is stable in a very wide pH range (pH 1-14), but zirconia surface has relatively low reactivity (more difficult to bond different functional groups to the surface), which signihcantly hmits a selection of available stationary phases. 

A few applications have employed conventional packed columns, although recent developments in new thermally stable stationary-phase materials have generated a renewed interest and the temperature stability of the different stationary-phase materials has been reviewed by Claessens and van Straten [43]. The new materials have included stable metal oxide materials, based on zirconia (Figures 18-4 and 18-5) and titania [44, 45] and hybrid phases combining silica and methylene or ethyl bridges [46]. These have been applied in a number of applications to pharmaceutical compounds (Table 18-1). 

The principal limitation of the use of superheated water has been the thermal instability of conventional ODS-silica-based stationary phases, which are unstable above 70°C or 80°C. Early work concentrated on PS-DVB columns, which were stable up to 220°C. Then zirconia-based PBD and ODS bonded... 

Lewis Base-Modified Zirconia as Stationary Phases for HPLC... 

Another possibility is the use of alternative stationary phases. A strong trend of the last decade is the employment of spedalty phases in challenging and complex separations. Thus, newer Cg, NH2, CN, mixedmode phases (materials incorporating both ion exchange and reversed-phase moieties), new polymeric phases, and zirconia-based materials offer attractive stationary-phase selectivities. 

The developments of the Lewis base-modified zirconia and mixed-oxide containing zirconia as stationary phases for high-performance liquid chromatography (HPLC) are reviewed. In this context, the preparation methods of porous spherical zirconia, and zirconia supports for HPLC based on modification with fluoride, phosphate, phos-phonate, carboxylic acid, phenols, and protein, as well as cyclodextrin derivative, are covered. The application of modified-zirconia in capillary electrochromatography (CEC) is also discussed. 

Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc. 2 Lewis Base-Modified Zirconia as Stationary Phases for HPLC... 

The ion-exchange properties of zirconia-silica surfaces were also evaluated by Chicz, Shi, and Regnier - however, their study was conducted on surfaces modified with a layer of PEI. A number of different stationary phase base support materials were employed in their study including zirconia-silica. They found that retention was dependent on the amount of PEI bound to the surface, leading them to suggest that base materials with similar... 

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