The characterization and evaluation of three novel 5-microm HPLC column packings, prepared using ethyl-bridged hybrid organic/inorganic materials, is described. These highly spherical hybrid particles, which vary in specific surface area (140, 187, and 270 m(2)/g) and average pore diameter (185, 148, and 108 A), were characterized by elemental analysis, SEM, and nitrogen sorption analysis and were chemically modified in a two-step process using octadecyltrichlorosilane and trimethylchlorosilane. The resultant bonded materials had an octadecyl surface concentration of 3.17-3.35 micromol/m(2), which is comparable to the coverage obtained for an identically bonded silica particle (3.44 micromol/m(2)) that had a surface area of 344 m(2)/g. These hybrid materials were shown to have sufficient mechanical strength under conditions normally employed for traditional reversed-phase HPLC applications, using a high-pressure column flow test. The chromatographic properties of the C(18) bonded hybrid phases were compared to a C(18) bonded silica using a variety of neutral and basic analytes under the same mobile-phase conditions. The hybrid phases exhibited similar selectivity to the silica-based column, yet had improved peak tailing factors for the basic analytes. Column retentivity increased with increasing particle surface area. Elevated pH aging studies of these hybrid materials showed dramatic improvement in chemical stability for both bonded and unbonded hybrid materials compared to the C(18) bonded silica phase, as determined by monitoring the loss in column efficiency through 140-h exposure to a pH 10 triethylamine mobile phase at 50 degrees C.

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A series of HPLC bonded phases containing an internal carbamate group were studied by changing the terminal N-alkyl group from C(8)H(17) to C(18)H(37) in increments of two methylene units, i.e., C(8), C(10), C(12), C(14), C(16), and C(18). Each material was prepared via bonding of silica with the respective 3-(chlorodimethylsilyl)propyl N-alkylcarbamate silane. The materials were compared under reversed-phase conditions using a test mixture of nonpolar, polar, and basic compounds in a 65:35 (v/v) methanol/20 mM KH(2)PO(4)/K(2)HPO(4), pH 7, mobile phase. Retention factors were found to generally increase from the C(8) length to the C(12)-C(16) lengths but decreased for the C(18) length. Retention factors were also measured as a function of three ligand surface concentrations for the C(12), C(14), and C(18) materials. In this study, retention generally decreased with increasing surface concentration, especially for the C(18) chain length. Changes in particle surface area and porosity caused by bonding did not fully account for the observed changes in retention factors. Peak shapes for the basic analytes propranolol and amitriptyline were also studied as a function of N-alkylcarbamate chain length and surface concentration. Tailing factors were unaffected by chain length and only weakly dependent on surface concentration. By comparison, tailing factors decreased significantly as surface concentration increased for a set of conventional C(18) alkyl packings.