Chromatography Configurations

Chromatography techniques can be further classified according to configuration—how the stationary phase is contained, how the mobile phase is configured with respect to the stationary phase in terms of physical state (gas or liquid) and positioning, and how and in what direction the mobile phase travels in terms of gravity, capillary action, or other forces. 

---

FIGURE 11.14 The classic open-column chromatography configuration with fraction collector. 

Jiang Y-S, Kurimoto Y, Shimamura T, Ko-chi N, Ohashi N, Mukai Y and Koyama Y (1996) Isolation by high-pressure liquid chromatography, configurational determination by H-NMR, and analyses of electronic absorption and Raman spectra of isomeric spheroidene. Biospectroscopy 2 47-58 Kandori H, Sasabe H and Mimuro M (1994) Direct determination of a lifetime of the Sj state of /J-carotene by femtosecond time-resolved fluorescence spectroscopy. J Am Chem Soc 116 2671-2672... 

Figure 5.4 Schematic diagrams of a heait-cut valve configuration system. Reprinted from Journal of Chromatography, 602, S. R. Villasenor, Matrix elimination in ion cliromatography by heart-cut column switching techniques , pp. 155-161, copyright 1992, with permission from Elsevier Science.

Figure 11.3 Typical configuration for the on-line coupling of an achiral and chiral cliro-matograpliic system by means of a switching valve. The non-enantio-resolved solute is isolated on the achiral phase and then stereochemically separated on the chiral phase. Reprinted from G. Subramanian, A Practical Approach to Chiral Separation by Liquid Chromatography, 1994, pp. 357-396, with permission from Wiley-VCH.

It is basically a fractionation process that depends not only on molecular size, but also on chemical composition, stereo-configuration, branching, and crosslinking. For multicomponent systems, fractionation with different ion polymolecularity, chemical heterogeneity and sequence length distribution, solubility or elution fractionation is of primary importance. Therefore, gel permeation chromatography or size exclusion chromatography is used as an important tool for the characterization of PBAs. 

Another class of configurationally stable a-mctallo amines is derived from the N-tert-butoxy-carbonyl-protected piperidines 32 and 3516, l7. Addition of the lithiated piperidines to aldehydes leads to mixtures of the anti- and. yin-diastereoiners. Although the diastereoselectivity is low, the diastereomers can be readily separated by chromatography since the. vyn-isomer is often in a cyclized form 34. The stereochemistry of the products obtained from piperidines 32 are consistent with an equatorial a-lithiation followed by addition to the aldehyde with retention of configuration. However, with piperidine 35 selective axial lithiation is observed. 

When the latter adduct (R = CFI3), purified by chromatography, is treated with sodium azide (inversion of configuration) and subsequently subjected to alkaline hydrolysis and hydrogenation, the enantiomerically pure 2-amino-3-hydroxycarboxylic acid results102 ... 

---