Planar chromatography separation material

Often, planar chromatography is used as a preparative step for the isolation of single components or classes of components for further chromatographic separation or spectroscopic elucidation. Many planar chromatographic methods have been developed for the analysis of food products, bioactive compounds from plant materials, and essential oils. 

This chapter highlights various ionization techniques that can be conducted under atmospheric conditions for the analysis of drugs of abuse and controlled substances, with particular emphasis on TLC, a technique in which mixtures are separated on a thin layer of an adsorbent material. Recent advances in chromatography, such as planar chromatography coupled to MS, have allowed for significant progress in the field [4]. 

Normal- or reverse-phase silica TLC is now complemented with separation methods that use novel stationary phases, such as silica gel particles bound into a polymer membrane (available commercially as Empore media). While the predominant use of these carriers have been in solid-phase extraction, TLC can be accomplished with silica gel in an Empore membrane. Affinity chromatography can also be accomplished in a planar format, and, especially in conjunction with MALDI mass spectrometry, will constitute a growing segment of planar chromatography. In these cases, the background materials expected to contribute to the mass spectrum may vary. However, the basic aspects of planar chromatographic separation remain similar. 

For planar chromatography (PC and TLC), retardation factors, Rf values, for standards and unknowns are compared by chromatographing them simultaneously so as to eliminate variations in laboratory materials and conditions. For column separations, retention times, f, or volumes, Vg, are compared by chromatographing standards and unknowns sequentially under stable conditions with as little time between runs as possible. 

The radial separation in the earlier example is not the most efficient way to perform surface chromatographic separations. A square planar thin-layer chromatography (TLC) plate (not to be confused with the theoretical plates discussed previously ) may have a line of spots containing sample mixtures and reference standard materials deposited just above one edge. Submerge that edge in solvent to a level just below the line of spots, and capillary attraction... 

Similarly, the reaction of 3-halo-1-alkenes with tetrabutylammonium tricarbonyl-(nitrosyl)ferrate (TBAFe) gives T -allyl(tricarbonyl)(nitrosyl)iron complexes. Treatment of Y-bromo-a,p-unsaturated esters or amides with potassium tricarbonyl-(nitrosyl)ferrate provides planar chiral T] -allyl(dicarbonyl)(nitrosyl)iron complexes. Enantiopure amides as starting materials lead to a low diastereoselectivity, whereas no diastereoselectivity is observed for the chiral esters. The diastereoisomers of the amide-substituted allyliron complexes can be conveniently separated by column chromatography (Scheme 4-80). ... 

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