Porous inorganic/organic hybrid particles for chromatographic separations and process for their preparation

#Packing materials for liquid chromatography (LC) are generally classified into two types: organic materials, e.g., polydivinylbenzene, and inorganic materials typified by silica. Many organic materials are chemically stable against strongly alkaline and strongly acidic mobile phases, allowing flexibility in the choice of mobile phase pH. However, organic chromatographic materials generally result in columns with low efficiency, leading to inadequate separation performance, particularly with low molecular-weight analytes. Furthermore, many organic chromatographic materials shrink and swell when the composition of the mobile phase is changed. In addition, most organic chromatographic materials do not have the mechanical strength of typical chromatographic silicas.

#Due in large part to these limitations, silica is the material most widely used in High Performance Liquid Chromatography (HPLC). The most common applications employ silica that has been surface-derivatized with an organic functional group such as octadecyl (C18), octyl (C8), phenyl, amino, cyano, etc. As stationary phases for HPLC, these packing materials result in columns that have high efficiency and do not show evidence of shrinking or swelling.

#Silica is characterized by the presence of silanol groups on its surface. During a typical derivatization process such as reaction with octadecyldimethylchlorosilane, at least 50% of the surface silanol groups remain unreacted. These residual silanol groups interact with basic and acidic analytes via ion exchange, hydrogen bonding and dipole/dipole mechanisms. The residual silanol groups create problems including increased retention, excessive peak tailing and irreversible adsorption of some analytes. Another drawback with silica-based columns is their limited hydrolytic stability. First, the incomplete derivatization of the silica leaves patches of bare silica surface which can be readily dissolved under alkaline conditions, generally pH>8.0, leading to the subsequent collapse of the chromatographic bed. Secondly, the bonded phase can be stripped off the surface under acidic conditions, generally pH<2.0, and eluted off the column by the mobile phase, causing loss of analyte retention, and an increase in the concentration of surface silanol groups.

#The present invention may be further illustrated by the following non-limiting examples describing the preparation of porous inorganic/organic hybrid particles, and their use.

#An organoalkoxysilane and tetraethoxysilane (all from Gelest Inc., Tullytown, Pa.) are mixed with ethanol (HPLC grade, J. T. Baker, Phillipsburgh, N.J.) and 0.1N hydrochloric acid (Aldrich Chemical, Milwaukee, Wis.) in a flask. The resulting solution is agitated and refluxed for 16 h in an atmosphere of argon or nitrogen. Ethanol and methanol (if applicable) are removed from the flask via distillation at atmospheric pressure. Residual alcohol and volatile species are removed by heating at 115-140° C. for 1-2 h in a sweeping stream of inert gas or by heating at 125° C. under reduced pressure for 1-2 h. The resulting polyorganoalkoxysiloxanes are colorless viscous liquids. The product numbers and the respective chemical formula of the organotrialkoxysilanes used in the copolymerization with tetraethoxysilane are listed in Table 1. The specific amounts of starting materials used to prepare these products are listed in Table 2.

#TABLE 1 Used in Organoalkoxysilane Organic Group Products Chemical Formula Name 1a, b, c CH3Si(OCH2CH3)3 methyl 1d C2H5Si(OCH2CH3)3 ethyl 1e C6H5Si(OCH2CH3)3 phenyl 1f, g, h, i, j, (CH3CH2O)3Si(CH2)2Si(OCH2CH)3 ethane bridge 1k, l H2C═CHSi(OCH2CH3)3 vinyl 1m, n, o H2C═C(CH3)CO2C3H6Si(OCH3)3 methacryloxypropyl 1p, q H2C═CHC6H4C2H4Si(OCH3)3 styrylethyl