Chemically modified stationary phases

Figure 11.23 Qualitative prediction of the elution order reversal of cis- and frans-androsterone. (Left) Anal5dical and preparative sample sizes. High concentration band profiles calculated with the LeVan-Vermeulen isotherm model. Inset experimental data [23], Stationary phase silica modified with a pH 6.8 phosphate buffer. Mobile phase (9 1) acetonitrile-dichloromethane, 0.98 mL/min. Samples, cis-androsterone 0.026 and 5.2 mg, trans-androsterone 0.15 and 1.8 mg. (Right) Band profiles calculated with the competitive Langmuir model. Reproduced with permission from S. Golshan-Shirazi, J.-X. Huang and G. Guiochon, Anal. Chem., 63, (1991) 1147 (Fig. 8). ( )1991, American Chemical Society.

Chiral stationary phases in tic have been primarily limited to phases based on normal or microcrystalline cellulose (44,45), triacetylceUulose sorbents or siHca-based sorbents that have been chemically modified (46) or physically coated to incorporate chiral selectors such as amino acids (47,48) or macrocyclic antibiotics (49) into the stationary phase. 

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. ... 

The most widely used columns contain a chemically modified silica stationary phase, with the chemical modification determining the polarity of the column. A... 

Solutions to the above problea are required if efficient open tubular colunns are to be prepared. The energy of the saooth glass surface can Sse Increased by roughening or chemical Modification, or the surface tension of the stationary phase can be lowered by the addition of a surfactant. Roughening and/or cheMical modification etre the most widely used techniques for column preparation the addition of a surfactant, although effective, modifies the separation properties of the stationary phase and may also limit the thermal sted>ility of columns prepared with high temperature stable phases. 

Some selected applications (chemical class, mobile phase, stationary phase, column, detector) are as follows fatty acids, C02, PEG or CN-PS, OTC, FID organotin, C02, PhMe-PS, OTC, FPD [305], ThepSFC-ICP system is an effective tool for speciation of metal-containing compounds [362], even in the presence of modifiers to control the retention of components. 

C. Marutoiu, M. Filip, C. Tigae, V. Coman, R. Grecu and G. Marcu, Synthesis and characterization of alumina R chemically modified with w-octyl for use as a stationary phase in TLC. J. Planar Chromatogr.-Mod. TLC 16 (2003) 186-191. 

Because of the good separation capacity chemically modified stationary phases were proposed for the rapid and economical analysis of peppermint polyphenols [126],... 

I. Fecka and W. Cisowski, TLC determination of tannins and flavonoids in extracts of some Erodium species using chemically modified stationary phases. J. Plan. Chromatogr.—Mod. TLC 15 (2002) 429-432. 

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. 

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