New Inorganic-Organic Hybrid Materials for HPLC Separation Obtained by Direct Synthesis in the Presence of a Surfactant

Abstract

Nanostructured, mesoporous inorganic–organic hybrid xerogels were reproducibly synthesized by a sol–gel procedure. For the introduction of long alkyl chains into inorganic polymers, trifunctional n‐alkyltrialkoxysilanes of the type CH3(CH2)nSi(OR)3 (n = 7, 11, 17; R = CH3, C2H5) were co‐condensed with Si(OEt)4 (TEOS). The synthetic pathway involves the employment of n‐hexadecylamine as template and catalyst. The xerogels obtained by the present procedure consist of uniform spherical particles with a diameter of about 1 μm. The composition of the new materials was determined by 13C and 29Si cross polarization magic angle spinning (CP/MAS) NMR spectroscopy. In addition, the degree of organization was investigated by small angle X‐ray and electron diffraction. In accordance with 13C CP/MAS NMR spectroscopic measurements, the alkyl chains form a crystalline arrangement within the silica polymer. Brunauer–Emmett–Teller (BET) adsorption measurements confirm specific surface areas of up to 1400 m2/g. The material properties prove the xerogels to be suitable as stationary phases in high‐performance liquid chromatography (HPLC). These novel mesoporous, nanostructured materials have been successfully employed in HPLC for the first time. Different standard reference materials (SRMs) containing polycyclic aromatic hydrocarbons have been separated with the xerogels described in the present work.

Synthesis and Characterization of Hybrid Materials Consisting of n-octadecyltriethoxysilane by Using n-Hexadecylamine as Surfactant and Q0 and T0 Cross-Linkers

“…The main reason of such a phenomenon is not yet clear, it could be related to the un-hydrolysis Me-Si steric factor of remaining Me on the X3 polysiloxane surface affecting the C 18 chain not to bend away to form a gauche conformation, thus enhancing the C–H Wander Val forces to form sort of stabilizing straight line chains as in Scheme 3. This proposal is compatible with the decrease in the trans conformation at the expense of the alternative gauche conformation increasing upon increasing the temperature [9,28–30]. …”

“…Characteristic peaks at approximately δ = 14.0 ppm are assigned to the carbon atom of CH 3 and the carbon atom of the silicon adjacent methyl groups (SiCH 2 ) in the Si–O–Si substructure δ = 22.8 ppm is assigned to CH 2 CH 3 and SiCH 2 C H 2 are significant for all the stationary phases. Weak signals of 13 C were assigned to residual Si–OR (R = Me or Et) functionalities at around δ = 17.0 and 57.9 ppm, attributed to non-hydrolyzed EtO ( X1 ) or MeO ( X2 and X3 ) silica functional groups, which point to a high degree of hydrolysis compared to the literature [7,9]. δ = −3.6 ppm is assigned to SiMe in case of using MeSi(OMe) 3 .…”

Spherical β-cyclodextrin-silica hybrid materials for multifunctional chiral stationary phases

“…Organic-inorganic hybrid materials that combine the advantages of the organic and inorganic units are receiving considerable attention for applications in separation, catalysis and electronics [28][29][30][31][32][33][34]. Such materials were endowed with new functions and features owing to the tunable functional organic groups in the pore walls or channels, which could achieve chromatographic separation not only on the surface of the materials but also at the inner part of the material so as to increase effective separation.…”

Ordered, Mesoporous Metal Phosphonate Materials with Microporous Crystalline Walls for Selective Separation Techniques

“…Porous silica materials surface‐modified by organic groups were used in liquid chromatography and CEC separation in the form of monolithic columns 53, 54. The organic–inorganic mesoporous hybrid materials (PMOs) in the form of packed columns were used for the separation of neutral compounds such as alkylbenzenes and polycyclic aromatic hydrocarbons 26–28. For the present mesoporous EDTMP–Me (Me: Ti, Zr, V, Al) hybrids, baseline separation of acidic, basic, and neutral compounds could be achieved under suitable pH values, and some analytes typical in the literature were chosen.…”

“…The design of PMO‐ and phosphonate‐based adsorbents with organic ligand groups grafted or incorporated onto the surface of the pore channels for the removal of toxic metal ions from solution has been reported extensively 24, 25. PMOs and organically modified mesoporous silicas have been demonstrated as the stationary phases in reverse‐phase high‐performance liquid chromatography (HPLC) in the form of packed columns, for the separation of only neutral compounds 26–28. However, packed columns usually result in low resolution as a result of peak broadening, which impairs the separation efficiency of these hybrid materials, and gram‐scale PMOs are needed for packed columns, leading to high‐cost consumption in chromato­graphic separation 29.…”