Principles of chromatography

Analysis of complex mixtures often requires separation and isolation of components, or classes of components. Examples in noninstrumental analysis include extraction, precipitation, and distillation. These procedures partition components between two phases based on differences in the components physical properties. In liquid-liquid extraction components are distributed between two immiscible liquids based on their similarity in polarity to the two liquids (i.e., like dissolves like ). In precipitation, the separation between solid and liquid phases depends on relative solubility in the liquid phase. In distillation the partition between the mixture liquid phase and its vapor (prior to recondensation of the separated vapor) is primarily governed by the relative vapor pressures of the components at different temperatures (i.e., differences in boiling points). When the relevant physical properties of the two components are very similar, their distribution between the phases at equilibrium will result in shght enrichment of each in one of the phases, rather than complete separation. To attain nearly complete separation the partition process must be repeated multiple times, and the partially separated fractions recombined and repartitioned multiple times in a carefully organized fashion. This is achieved in the laborious batch processes of countercurrent liquid—liquid extraction, fractional crystallization, and fractional distillation. The latter appears to operate continuously, as the vapors from a single equilibration chamber are drawn off and recondensed, but the equilibration in each of the chambers or plates of a fractional distillation tower represents a discrete equihbration at a characteristic temperature. 

In all chromatographic techniques, the sample to be separated passes through the system carried by a solvent (the mobile phase). The rate at which 

Thin layer chromatography (TLC) Solid (silica gel) Liquid (solvent, often a mixture). Also called developer. 

Resolution (R) is the measure of the chromatographic separation of two components. Ideally, mixtures should be completely separated, but in many instances spots or peaks will overlap (co-elute). For gas chromatography, where the components are isolated as Gaussian peaks, the resolution is given by  

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The basic principle of chromatography separations can be described by thermodynamics using the distribution coefficient K (12) ... 

Isocratic versus Gradient Elution. The principles of chromatography just described hold true for isocratic elution schemes, in which the nature of the mobile phase remains constant throughout the de-... 

Chromatographic Separation. Chromatographic separation of protein mixtures has become one of the most effective and widely used means of purifying individual proteins. A more detailed discussion of the principles of chromatography and their application to the separation of protein mixtures is presented in Experiment 2 and is also illustrated in Experiments 8 and 10. 

The handbook contains also a general part, which deals with the equipment and its use, standard conditions, and special working techniques. The quantitative evaluation and the especially important isotope techniques are discussed in detail. The final chapter explains the theoretical principles of chromatography comprehensively and in a new view. Numerous illustrations and tables comment in a graphic way upon the concise and clear text and contribute to make this handbook an indispensable aid for each laboratory. 

The primary aim of this book is to provide readers interested in solid sample pretreatment with an overview of available techniques for development of this step of the analytical process. The title of the book is intended to reflect that it is mainly concerned with the dissolution or removal of target analytes from solid samples. Once they have selected the technique most closely fitting their intended purpose, readers can obtain a deeper knowledge about the technique of choice in the specialized literature — in fact, providing a thorough description of each of the wide variety of sample pretreatment techniques available at present was obviously outside the scope of a book like this. In fact, only those aspects that can be illustrated with reasonable concision are dealt with specifically in it. For identical reasons, the book does not touch on the subsequent steps of the analytical process. The authors therefore assume that the reader will be acquainted with the general principles of chromatography in its different variants, as well as with those of commonplace molecular optical and electroanalytical techniques, and atomic and mass spectrometries. 

The purpose of this article was to provide the reader with a basic understanding of capillary electrophoresis and to describe how a technique such as MEKC uses basic principles of chromatography to perform separations which are not possible electrophoretically. As the applications for electrokinetic chromatography rapidly expand, the future direction will develop on two fronts ... 

There are many good analytical textbooks now available, however most concentrate on a detailed discussion of analytical techniques (e.g. those based upon the principles of chromatography and spectroscopy), and at the expense of the more fundamental considerations of why the analysis is to be carried out and how the samples are to be taken. Whilst most modern texts will introduce the reader to the importance of sampling, many gloss over the serious errors which may be introduced into the results if the sampling protocol is not undertaken in a logical and statistically significant manner. 

Guiochon, G. Basic Principles of Chromatography in Ullmann s Encyclopedia of Industrial Chemistry, Vol. B5, VCH Verlagsgesellschaft, 1994. 

A technique that overcomes these limitations is based on the principles of chromatography, as shown in Fig. 7.20. The catalyst, in any form, is packed in a tube. A pulse of argon, injected into helium carrier gas, is... 

Analysis method using the principles of chromatography for samples in the gaseous or vapor state. 

Qualitative analysis method that uses the principles of chromatography for substances in the dissolved state. 

In order to appreciate the forces that are responsible for chromatographic resolution, we need to review some of the principles of chromatography. The elution of a sample through a chromatography column is accomplished by a partitioning of the sample between a stationary phase and mobile phase. In GC the... 

The book edited by Harrison and Rapso-manikis (1989) on environmental analysis using chromatography interfaced with atomic spectroscopy has chapters on basic principles of chromatography and AAS, interfaces between liquid chromatography and AAS and determination of individual elements. The book by Kebbekus and Mitra (1998) contains a chapter devoted to chromatographic methods, a discussion of which is also included in chapters on methods for air, water and solid sample analyses. 

In the first section of this chapter a brief review of stereochemistry is provided along with a justification for why scientists need to separate enantiomers. The following section provides a brief review of the principles of chromatography with an emphasis on chiral chromatography. In the next section we provide a working definition of what molecular modeling means followed by a section describing the different kinds of commercially available stationary phases and how they work. The... 

The general principles of chromatography have been discussed in Chapter 2. However, a more detailed account in the context of GC is presented herein the reader is also referred to the Glossary for additional detail and explanations of the terminology used. The treatment of theoretical aspects is at a level which should enable the analyst to obtain maximum efficiency and performance from the system and application. 

The 5th edition of Chromatographic Methods reflects these many changes across all fields of chromatography. The principles of chromatography, however, remain the same although an understanding of the theoretical aspects and principles has become more important in order to appreciate the influence various parameters have on the separation process, particularly... 

The general principles of chromatography, which were developed in (Chapter 26. and the mathematical relationships summarized in Section 26E are applicable to GC with only minor modifications that arise from the compressibility of gaseous mobile phases. 

Direct analysis of lipid classes enables faster and more efficient usage of analytical resources and sample material. Many of the direct analysis techniques are derived from the basic principles of chromatography described above. However, they have evolved specific instrumentation to enable (in most cases) improved separation... 

The sorption process can also be studied in column experiments where the movement of the chemical through the soil can be monitored as a function of soil type, column dimensions, and flow rates of water acting as the eluant. Application of the principles of chromatography, in particular the transport equations for the... 

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