Available stationary phase, definition

In the first section of this chapter a brief review of stereochemistry is provided along with a justification for why scientists need to separate enantiomers. The following section provides a brief review of the principles of chromatography with an emphasis on chiral chromatography. In the next section we provide a working definition of what molecular modeling means followed by a section describing the different kinds of commercially available stationary phases and how they work. The... 

Trying to determine which column is ideal for a specific analysis can be difficult with over 1000 different columns on the market [74]. A proper choice implies a definition of parameters such as column material, stationary phase (polarity), i.d., film thickness and column length. Guides to column selection are available [74,75]. The most important consideration is the stationary phase. When selecting an i.d., sample concentration and instrumentation must be considered. If the concentration of the sample exceeds the column s capacity, then loss of resolution, poor reproducibility and peak distortion will result. Film thickness has a direct effect on retention and the elution temperature for each sample compound. Longer columns provide more resolving probe, increase analysis times and cost. 

Different capillary columns are available for organic acid separation and analysis. In our laboratory, the gas chromatography column in all GC-MS applications is crosslinked 5% phenyl (poly)methyl silicone, 25 m internal diameter 0.20 mm stationary phase film thickness 0.33 pm (Agilent HP-5, DB-5, or equivalent). Several instrument configurations are commercially available, which allow for positive identification of compounds by their mass spectra obtained in the electron impact ionization mode. A commercially available bench-top GC-MS system with autosampler (Agilent 6890/5973, or equivalent) is suitable. Software for data analysis is available and recommended. The use of a computer library of mass spectra for comparison and visualization of the printed spectra is required for definitive identification and interpretation of each patient specimen. 

Often, organic chemists use a dimensionless amount loaded normalized to the weight of packing in the column, Lv. (Eq. (7.43)). This less rigorous definition does not take into account the number of sites available on the stationary phase for the product or for the impurities. Note that from column to column or repack to repack, the amount loaded at a constant Lf or a constant is a function of the porosity. 

The capacity is closely related to the number of active sites of the stationary phase per volume or mass unit. Practically, there are two definitions corresponding to two different approaches to the problem. On the one hand, there is the linear capacity and, on the other, the maximum available capacity. 

However, the real potential of enantioselective chromatography for the preparative separation of optical isomers was definitely established in 1973 by Hesse and Hagel who introduced fully acetylated cellulose (triacetylcellulose) as a new efficient chiral CSP [14]. They successfully achieved the preparative separation of the enantiomers of various chiral compounds. For many years, triacetylcellulose was practically the only chiral stationary phase available for preparative separations and it has been used for the chromatographic resolution of a broad variety of chiral molecules [1-3, 15, 16]. 

According to International Union of Pure and Applied Chemistry (lUPAC)," chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary while the other moves in a definite direction. HPLC is then defined as an analytical separation technique used to detect and quantitate analytes of interest in more or less complex mixtures and matrices that uses elevated pressures to force the liquid through the bed of the stationary phase. " The bed is most often located in a column. Since almost four decades of its inception, HPLC technique has advanced and there is enormous literature available on this technique. 

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