Chromatographic techniques liquid chromatography

Hurst, W.J., Martin, R.A. Jr, Tarka, S.M. Jr. and Hall, G.D., Authentication of cocoa in maya vessels using high performance liquid chromatographic techniques, J. Chromatography, 466,279,1989. 

Chromatographic techniques liquid-liquid and gas-liquid chromatography (GLC)... 

The quantitative analyses of reactants and reaction products were performed by chromatographic techniques (gas chromatography, liquid chromatography, etc.)... 

The most recently developed chromatographic technique, gas chromatography, was first described by Martin and James in 1952 and has become the most sophisticated and widely used of all chromatographic methods, particularly for mixtures of gases or for volatile liquids and solids. Separation times of a matter of minutes have become commonplace even for very complex mixtures. The combination of high resolution, speed of analysis, and sensitive detection have made GC a routine technique used in almost every chemical laboratory. 

Conventional planar and nonplanar as well as thin- and thick-layer liquid chromatographic techniques require few instruments and are rather simple. Among the planar layer liquid chromatographic techniques, paper chromatography (PC) and its various versions, developed in the 1940s by Martin et al., have to be mentioned first (1). Thin-layer chromatography (TLC), discovered by Ismailov and Shraiber (2) as well as B k sy (3). improved by Kirchner et al. (4), and standardized and spread by Stahl et al. (5,6), contributed to the isolation and analysis of many natural and synthetic substances. Today, versions of this classical chromatographic technique are indispensable in different fields of scientific research and practice. 

While spectroscopic techniques will give a qualitative identification of the surfactant, detailed characterization of the hydrophobic portion of the molecule is almost always performed by gas chromatography. Because most anionic surfactants lack volatility, the compounds are desulfonated or derivatized before gas chromatographic analysis. Liquid chromatography is also suitable for the analysis. Although HPLC provides less information about isomers than does GC, it is usually possible to analyze the sample directly, without desulfonation or derivatization. These techniques are discussed in Chapters 7 and 8. 

Analytical separations may be classified in three ways by the physical state of the mobile phase and stationary phase by the method of contact between the mobile phase and stationary phase or by the chemical or physical mechanism responsible for separating the sample s constituents. The mobile phase is usually a liquid or a gas, and the stationary phase, when present, is a solid or a liquid film coated on a solid surface. Chromatographic techniques are often named by listing the type of mobile phase, followed by the type of stationary phase. Thus, in gas-liquid chromatography the mobile phase is a gas and the stationary phase is a liquid. If only one phase is indicated, as in gas chromatography, it is assumed to be the mobile phase. 

The major chromatographic techniques can also be categorised according to tbe nature of the mobile phase used -vapour phase chromatography for when a gas is the mobile phase and liquid chromatography for when a liquid is the mobile phase. 

HPLC separations are one of the most important fields in the preparative resolution of enantiomers. The instrumentation improvements and the increasing choice of commercially available chiral stationary phases (CSPs) are some of the main reasons for the present significance of chromatographic resolutions at large-scale by HPLC. Proof of this interest can be seen in several reviews, and many chapters have in the past few years dealt with preparative applications of HPLC in the resolution of chiral compounds [19-23]. However, liquid chromatography has the attribute of being a batch technique and therefore is not totally convenient for production-scale, where continuous techniques are preferred by far. 

Countercurrent chromatography (CCC) refers to a chromatographic technique which allows the separation of solutes in a two-phase solvent system subjected to a gravitational field. Two immiscible liquid phases, constituted by one or more solvents or solutions, are submitted to successive equilibria, where the solutes to be separated... 

High-pressure liquid chromatography (HPLC) is a variant of the simple column technique, based on the discovery that chromatographic separations are vastly improved if the stationary phase is made up of very small, uniformly sized spherical particles. Small particle size ensures a large surface area for better adsorption, and a uniform spherical shape allows a tight, uniform packing of particles. In practice, coated Si02 microspheres of 3.5 to 5 fxm diameter are often used. 

Another chromatographic method is pyrolysis/gas-liquid chromatography. The sample is mixed with P205 and heated to 400°C. This technique yields the chain length distribution of the fatty acids initially used [107],... 

---