Classical liquid column chromatography

Thin layer chromatography is reproducible, relatively easy to perform, quick, and inexpensive. The resolution of TLC is greater than classical liquid column chromatography, although usually it is still not possible to resolve individual components from a complex mixture. It is, however, able to separate compound classes (e.g., aliphatic from aromatic) and its main use is,... 

Figure 7.1 Diagram of classical liquid column chromatography. The sample is introduced at the top of the column, and the different components travel downwards and are separated. They can be collected in sequence from the tap at the bottom.

Classic liquid column chromatography is rather time and solvent consuming, but is still used for preparative work because of the simple and low priced apparatus and column materials. 

Fig. 4.2.1. The classic liquid column chromatography set-up (gravity flow system). 1, solvent delivery 2, column 3, detection.

Classic paper chromatography like distribution chromatography is also carried out today in most cases in layers on a support sheet. To obtain low standard deviations extensive automatization from sample application to evaluation is necessary. The essential advantage in comparison to liquid column chromatography is the possibility of separating several samples side by side, because therefor usually no apparatus is required. 

Figure 21.14. Comparison of columns used in liquid chromatography. A Classical open column chromatography with large porous particle packings B HFLC with pellicular packings C HPLC with microparticulate packings.

OPEN-COLUMN CHROMATOGRAPHY. Liquid-column chromatography performed in the classical manner in a relatively large bore, usually glass column under gravity or low-pressure flow. 

This technique was based on the classic paper by Martin and Synge of 1941 [598], in which liquid-liquid column chromatography was used to separate amino acids. The paper contained the significant phrase -"the mobile phase need not be a liquid but may be a vapour". However, the idea was not pursued until A.T. James joined Martin in 1949. James has recently provided an entertaining account of their joint collaboration [431]. In the initial work, they could only attempt to separate those compounds which could be detected and quantified by titration. The first essays at separations were made with a column packed with... 

Nevertheless, for contaminated samples it is still necessary to carefully cany out a number of clean up procedures. Among them it should be cited classical liquid adsorption chromatography in columns, solid-phase extraction, gel-permeation chromatography, reduction of solvent volume and solvent exchange, which imply an important timing of the process. Their characteristics and operational procedure have been described in air monitoring, and will not be further detailed here. 

High Pressure Liquid Chromatography. This modem version of the classical column chromatography technique is also used successfully for separation and quantitative analysis of dyes. It is generally faster than thin-layer or paper chromatography however, it requires considerably more expensive equipment. Visible and uv photometers or spectrophotometers are used to quantify the amounts of substances present. 

The stationary phase matrices used in classic column chromatography are spongy materials whose compress-ibihty hmits flow of the mobile phase. High-pressure liquid chromatography (HPLC) employs incompressible silica or alumina microbeads as the stationary phase and pressures of up to a few thousand psi. Incompressible matrices permit both high flow rates and enhanced resolution. HPLC can resolve complex mixtures of Upids or peptides whose properties differ only slightly. Reversed-phase HPLC exploits a hydrophobic stationary phase of... 

Principles and Characteristics Column liquid chromatography is the parent of all other types of chromatography. The technique used by Tswett is now called classical open-column liquid chromatography or simply LC. In column chromatography the stationary phase is contained in a column and the mobile phase flows... 

The term liquid chromatography (LC) is applied to any chromatographic procedure in which the moving phase is liquid, as opposed to gas chromatography (GC) where a gas is utilized as a mobile phase (see discussion in Chapter 14). Classical column chromatography (see Section 15.1), paper chromatography—a forerunner of thin-layer chromatography (see Chapter 13), and HPLC are all examples of LC. This should clarify why it is inappropriate to further abbreviate HPLC to LC unfortunately, it is still commonly done. 

Classical column chromatography Solid (silica gel) Liquid (solvent, often a mixture). Also called eluent. 

Knowledge of the sample composition and the structure of its components simplifies the choice of the eluent and facilitates the prediction of the approximate elution order. Additionally, reference can be made to literature of classical column chromatography (7, 9, 66, 67). The exploitation of such results in HPLC represents no difficulties provided the eluent can be used with the detector of the liquid chromatograph. It should be kept in mind that the classical results are useful only to establish the chromatographic system for a particular separation but not to predict the exact retention data. 

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