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Bonded stationary phases chemical structure

The columns used for the GC separation of phytosterols are currently almost exclusively capillary columns with 0.1-0.3 mm internal diameter, and fused-silica capillary columns with chemically bonded stationary phases are commonly used (Abidi, 2001). The best separation of structurally very similar sterols, such as sitosterol and its saturated counterpart sitostanol, is obtained with slightly polar stationary phases like 5% diphenyl-95% dimethylpolysiloxane, and they are currently the most used columns for the separation of phytosterols (Lagarda et al., 2006). For detailed lists of different columns used in sterol analysis, see the papers by Abidi (2001) and Lagarda (2006). [Pg.337]

Structurally related compounds, dithiocaibamates (XIV), have fungicidal activity. Reversed-phase chromatography of copper dithiocarbamates was studied, and the Revalues were found to be linearly dependent on the chain length of the chelate, the water content of the mobile phase, and the number of carbon atoms of the chemically bonded stationary phase (93). [Pg.784]

Separation of enantiomers by physical or chemical methods requires the use of a chiral material, reagent, or catalyst. Both natural materials, such as polysaccharides and proteins, and solids that have been synthetically modified to incorporate chiral structures have been developed for use in separation of enantiomers by HPLC. The use of a chiral stationary phase makes the interactions between the two enantiomers with the adsorbent nonidentical and thus establishes a different rate of elution through the column. The interactions typically include hydrogen bonding, dipolar interactions, and n-n interactions. These attractive interactions may be disturbed by steric repulsions, and frequently the basis of enantioselectivity is a better steric fit for one of the two enantiomers. ... [Pg.89]

Reverse phase HPLC describes methods that utilize a polar mobile phase in combination with a nonpolar stationary phase. As stated above, the nonpolar stationary phase structure is a bonded phase—a structure that is chemically bonded to the silica particles. Here, typical column names often have the carbon number designation indicating the length of a carbon chain to which the nonpolar nature is attributed. Typical designations are C8, C18 (or ODS, meaning octadecyl silane), etc. Common mobile phase liquids are water, methanol, acetonitrile (CH3CN), and acetic acid buffered solutions. [Pg.375]

In an attempt to change and broaden the capabilities of the vancomycin CSP, the glycopeptide was derivatized with (R)- and (S )-(l-naphthylethyl) isocyanate (NEIC) and then bonded to a silica-gel support [48]. A variety of chiral compounds was tested on the two composite stationary phases and the results were compared with the ones obtained using the underivatized vancomycin CSP. The advantages of the NEIC derivatization were not as obvious or substantial as they were in the case of cyclodextrin phases [49]. Moreover, the exact chemical structures of the synthesized NEIC derivatives of vancomycin were not reported. [Pg.121]

Programmed temperature (120 -200°C) chiral separation on a 0.25-mm x 25-m open tubular column with a 0.25-nm-thick stationary phase containing 10 wt% fully methylated p-cyclodextrin chemically bonded to dimethyl polysiloxane. [From W. Vetter and W. Jun, Elucidation of a Polychlorinated Bipyrrole Structure Using Enantioselective GC," Anal. Chem. 3002, 74,4287.]... [Pg.533]

Chemical stability of carbon over the entire pH range has led to considerable interest in the development of carbon-based stationary phases for RPC. Porous graphitised carbon with sufficient hardness, well-defined and stable pore structure without micropores, which ensures sufficient retention and fast mass transfer can be prepared by a complex approach consisting of impregnation of the silica gel with a mixture of phenol and formaldehyde followed by formation of phenol-formaldehyde resin in the pores of the silica gel, then thermal carbonisation and dissolution of the silica gel by hydrofluoric acid or a hot potassium hydroxide. solution [48. The retention and selectivity behaviour of carbon phases significantly differs from that of chemically bonded pha.ses for RPC. Carbon adsorbents have greater affinity for aromatic and polar substances so that compounds can be separated that are too hydrophilic for adequate retention on a Cix column. Fixed adsorption sites make these materials more selective for the separation of geometric isomers [49]. [Pg.38]

Relatively few molecular separations have been studied from the utilitarian standpoint. One of these, the purification of fullerenes via 8 , is discussed on p. 170. In a reciprocal experiment the separation of 4 " , 6 , and 8 with a column using a chemically-bonded C o silica stationary phase has been re-ported. Chromatographic selectivity has been achieved for amino acid esters and alkali metal cations on silica-bonded calix[4]arene tetraesters, the structure of which has been explored by and Si-CP-MAS NMR. Silica-bonded calixarenes have also been used as packing materials for HPLC columns that are capable of separating disubstituted aromatics, peptides, and nucleosides. The HPLC separation of phenols using 6 ° as a constituent of the eluent has been described. ... [Pg.190]


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See also in sourсe #XX -- [ Pg.65 , Pg.67 ]




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Bonded phase phases

Bonded stationary phase

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Chemically bonded phases

Phase chemical

Stationary phase Bonded phases

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