Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Organic
Patent
1992-03-09
1994-07-05
Dees, Carl F.
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Organic
502158, 502407, 502414, B01J 2006, B01J 2022, B01J 2030
Patent
active
053267389
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a surface-modified material used in a wide variety of separation applications such as chromatography and electrophoresis.
More particularly, the invention pertains to a chemically modified mineral oxide such as silica, quartz or the like, which exhibits improved hydrolytic stability, larger organic coverage and superior separative capabilities when formed into various forms or shapes, such as porous beads or capillary tubes.
BACKGROUND OF THE INVENTION
Chemically modified silicas have been, and continue to be, widely used as supports in a great variety of chromatographic separations. With the aim of controlling its selectivity while reducing unwanted interactions with one or more compounds, numerous synthetic procedures have been developed to attach organic moieties (R) on the silica surface. Early work on the chemical modification of silica (Halasz and Sebastian, Angew. Chem. (Int. Ed.) 8:453 (1969); Deuel et al., Helv. Chim. Acta 119:1160 (1959)) described the use of an esterification reaction between surface silanol groups (SiOH) and an alcohol to give a structure of the following type: ##STR1## Although such materials were useful for many separations, their limited hydrolytic stability seriously precluded the extensive usage of these bonded phases, particularly in liquid chromatography which requires the use of aqueous eluents.
Currently, commercially available bonded phases are prepared by reacting selected organosilanes with the silica surface. Halogen- or alkoxy-substituted alkyldimethylsilanes are the most commonly used silanizing reagents. The resulting bonded support bears monolayer surface structures of the following type: ##STR2## By changing the structure of the R group, it is possible to produce bonded silicas with a great variety of organic groups, ranging from non-polar materials, for instance, octyl- and octadecyl-silicas commonly used as bonded supports in reversed-phase liquid chromatography, to ionic materials such as benzenesulphonic acid derivatives which are widely used in ion-exchange liquid chromatography. The preparation of these and similar materials are described in a number of publications (e.g., Roumeliotis and Unger, J. Chromatogr. 149:211 (1978) or Asmus et al. J. Chromatogr. 123:109 (1976)) and patents (Sebastian et al. U.S. Pat. No. 3,956,179; Hancok et al. U.S. Pat. No. 4,257,916; or Ramsden et al. U.S. Pat. No. 4661,248).
In a related approach, polymeric (multilayer) bonded stationary phases are prepared from bi- or tri-substituted organosilanes with the general formula X.sub.n SiR.sub.4-n, where X=alkoxy, halide or any easily hydrolyzed group, and n=2,3. The resulting polymeric bonded support bears repeating surface structures of the type ##STR3## where Y=--R (n=2) or --O-- (n=3) and the oxygen atom (--O--) is bonded either to a hydrogen (that is, as part of a free silanol, Si--O--H) or to another silicon atom (that is, as part of a siloxane linkage, Si--O--Si). A number of patents and publications describe the preparation of these materials (Kirkland and Yates, U.S. Pat. Nos. 3,722,181 (1973), and 3,795,313 (1974); Novotny et al., J. Chromatog. 83:25 (1973); Sander and Wise, Anal. Chem. 56:504 (1984)). Although in many instances these bonded supports provide satisfactory separations, the lack of control of the polymerization process seems to be a major contributor to such problems as irreproducible layer thickness and incomplete silanol condensation. This limitation has confined polymeric bonded stationary phases to applications where the presence of a multilayer is necessary and/or its thickness is relatively unimportant. As a consequence, the vast majority of liquid chromatographic separations are carried out with monolayer bonded phases.
The recent development of electrophoretic separations in a capillary format has promoted the extent of the silanization technology normally used in chromatography to the deactivation of the inner wall of the fused silica capillary. Thus, Jorgenson et al. (Science 222:266 (1983)) h
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Pesek Joseph J.
Sandoval Junior E.
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