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Chapter: Modern Analytical Chemistry: Chromatographic and Electrophoretic Methods

Liquid–Solid Adsorption Chromatography

In liquid–solid adsorption chromatography (LSC) the column packing also serves as the stationary phase.

Liquid–Solid Adsorption Chromatography

In liquid–solid adsorption chromatography (LSC) the column packing also serves as the stationary phase. In Tswett’s original work the stationary phase was finely di- vided CaCO3, but modern columns employ porous 3–10-μm particles of silica or alumina. Since the stationary phase is polar, the mobile phase is usually a nonpolar or moderately polar solvent. Typical mobile phases include hexane, isooctane, and methylene chloride. The usual order of elution, from shorter to longer retention times, is

olefins < aromatic hydrocarbons < ethers < esters, aldehydes, ketones < alcohols, amines < amides < carboxylic acids

For most samples liquid–solid chromatography does not offer any special advan- tages over liquid–liquid chromatography (LLC). One exception is for the analysis of isomers, where LLC excels. Figure 12.32 shows a typical LSC separation of two am- phetamines on a silica column using an 80:20 mixture of methylene chloride and methanol containing 1% NH4OH as a mobile phase. Nonpolar stationary phases, such as charcoal-based absorbents, also may be used.


 

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