Chemically bonded stationary phases characterization

Liquid-solid chromatography (LSC), sometimes referred to as normal phase or straight phase chromatography, is characterized by the use of an inorganic adsorbent or chemically bonded stationary phase with polar functional groups and a nonaqueous mobile phase... 

This chromatographic mode usually involves aliphatic chemically bonded stationary phases with, for example, octyl, octadecyl, or phenyl ligands. The mode of chromatography also is characterized by a mixed mechanism of solute retention Solute molecules interact specifically with the residual active sites of the silica matrix, whereas their interactions... 

SEM has been a primary tool for characterizing the fundamental physical properties of oxide materials for some time. For example, SEM is particularly useful for determining the particle shape and approximate size distribution of various silica materials used as supports in chemically bonded stationary phases for chromatography [8]. The visual images provide resolution at the micron to in some cases the submicron level so that surface morphology can be determined. This information is especially useful when evaluating a new synthetic approach to the formation of oxide materials. For example, a recently developed method... 

Buszewski, B., Gadza-la-Kopciuch, R. M., Markuszewski, M. L, Kaliszan, R. Chemically bonded silica stationary phases synthesis, physicochemical characterization, and molecular mechanism of reversed-phase HPLC retention. Anal. Chem. 1997, 69, 3277-3284. 

Silica-based stationary phases with a chemically bonded ligand on the surface can be characterized by the carbon content (grams of carbon per 100 g of packing) and by the bonding density (micromols of ligand bonded/square meter of initial silica surface area). 

Sandoval, I.E. and Pesek, I.I., Synthesis and characterization of a hydride-modified porous silica material as an intermediate in the preparation of chemically bonded chromatographic stationary phases, AnaZ. Chem., 61, 2067, 1989. 

Absorbance signals seen in NIR consist of combination and overtone bands of hydrogen bonds such as C-H, N-H, 0-H, and S-H, which are aroused by large force constants and small mass. NIR spectra thus cover precious information on chemical as well as physical properties of analyzed samples due to characteristic reflectance and absorbance patterns [121-123], which makes this analysis method applicable to the characterization of monolithic stationary phases. 

In the area of cyclodextrin ethers the -compound has been converted into a set of five tris-Tbdms ethers, all substituted at their various 6-positions, which were separated by hplc and characterized by n.m.r. spectroscopy. Related work applied to y-cyclodextrin gave the various 6,6 -disubstituted ethers. 5-Bromo-l-pentene was used to produce the 2-0-mono-4-pentenyl ether of P-cyclodextrin which was then permethylated and the product was chemically bonded to silica gel to form an efficient hplc stationary phrase for the separation of enantiomers. Peroctyl a-cyclodextrin has been studied as a chiral receptor for the ephedrinium ion. Various octyl ethers of a-, P- and y-cyclodextrin ranging in their substitution from the diethers to completely alkylated products were characterized by electrospray mass spectrometry and n.m.r. methods applied to methylated derivatives. The 2,6-didodecyl derivative of p-cyclodextrin has been used as a potentiometric sensor. In the field of aromatic ethers, naphthyl carboxylate substituents have been bonded at the 6-positions and the products were able to transfer excitation energy to complexed merocyanine held in the cavities of those molecules. These phototransfer processes were extremely efficient.P-Substituted cyclodextrin derivatives with p-allyloxybenzoyl or various benzyl substituents at 0-2 or 0-3 were incorporated by hydrosilylation to give hydromethylpolysiloxane polymers used as chiral phases for chromatographic resolution of enantiomers. Cyclodextrins with complex benzyl-like eth are illustrated in 22 and 23. The latter were prepared as artificial redox enzymes. 

Two types of stationary phases are most popular the polysiloxanes and polyethylene glycol phases. Both types of phases may be characterized as having the necessary high viscosity and the capability for crosslinking and/or chemical bonding with fused silica. One should note the presence of more recent additions to the capillary column family, namely, specialty columns designed for selected EPA methods, chiral separations, and gas-solid chromatographic separations. These specialty phases are considered in Section 3.11.6. 

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