Tswett chromatographic technique,

Adsorption chromatography. This chromatographic technique is best known because of its use in the last century as a preparative method of separation. Stationary phases have made a lot of progress since Tswett. who used calcium carbonate or sugar. The separation of organic compounds on a thin layer of silica gel or alumina with solvent as a mobile phase are examples of this type of chromatography. Solutes bond to the stationary phase because of physisorption or chemisorption interactions. The physico-chemical parameter involved is the coefficient of adsorption. 

CHROMATOGRAPHY. In 1903,Tswett, a Russian botanist, first described his attempts to separate colored substances hence, the origin of the term chromatography. Today, many of the compounds that are separated and identified by chromatographic techniques are colorless but new refinements in these techniques enable the food analyst to meeisure extremely minute amounts of many compounds. 

Although liquid-column methods were the first chromatographic techniques introduced (Tswett, 1905), they remained in the background for some time. Their recent revival may be due to the technical and theoretical advances of gas chromatography and to the standardization of sorbents introduced for TLC purposes. 

Despite these many differences, chromatography, and in fact all separations, have a deep underlying unity that is reflected both theoretically and historically. Chromatography is now (arguably) the most widely used analytical technique. Highly sophisticated chromatographic instruments are available from many manufacturers, but of course this was not always so. In fact, the word chromatograph was first coined in 1906 by Mikhail Tswett (1872-1919). 

The history of chromatography and adsorption chromatography, from its earliest pre-Christian antecedents to its explicit discovery by Tswett and its subsequent development by more recent workers, has been covered in great detail by other writers [e.g.. Refs. 1-4) for reasonably complete coverage]. These historical reviews emphasize the experimental side of adsorption chromatography almost to the exclusion of theoretical contributions, because advances in the method have been for the most part advances in technique. In the present brief section we will attempt to focus attention on the historical development of an understanding of the adsorption chromatographic process. 

Normal-phase liquid chromatography (NPLC) is the oldest chromatographic mode, discovered by M.S. Tswett more than 100 years ago. It has been the predominant mode in thin-layer chromatography (TLC) and low-pressure dry-column liquid chromatography before the introduction of reversed-phase technique, which is a preferred mode in high-performance liquid chromatography (HPLC). 

At the end of the 1930s, adsorption chromatography in columns as introduced by Tswett had become a powerful separation technique for plant extracts and natural products. Simultaneously, the need for a more rapid alternative suitable for identification of separated substances led to the invention of an open chromatographic system. In 1938, Izmailov and Shraiber reported the separation of belladonna alkaloids on a thin adsorbent layer, coated onto microscopic slides. Development of circular chromatograms was achieved by placing small amounts of various solvents to the center of samples previously applied as spots onto the layer. This method was an extremely rapid microtechnique requiring only small amounts of stationary and mobile phases. 

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