Chromatography, general classification

This type of gas chromatography falls into the general classification of chromatography. 

Residual solvents are the third general classification of impurities in pharmaceuticals. This class is described as inorganic or organic liquids used during the manufacturing process. Typically, these solvents can only be evaluated by gas chromatography and therefore will not be addressed in this chapter. 

Numerous extraction methods and techniques have been developed and reported, especially if one takes into account the variety of modifications. The most common and simple general classification of these methods is similar to that introduced in chromatography and based on the kind of phase to which the analyte is transferred. One can distinguish the extractions as liquid, solid, gas, and supercritical fluid phase extractions. More precise description specifies the two phases between which the analyte is distributed (e.g., liquid-liquid or solid-liquid [leaching] extractions). The latter methods are all called solvent extraction. 

General classification of the modes of thin-layer chromatography (TLC) is based on the chemical nature of the stationary and mobile phases. The following three types of thin-layer chromatography given are widely recognized as different modes ... 

There are several types of surfaces or interfaces that are of great practical importance and attracting fundamental interest. These general classifications include liquid-gas, liquid-liquid, liquid-solid, solid-gas, and solid-solid interfaces. Many examples of interfaces of natural and technological importance are available, for instance, oil-water interfaces in emulsions, air-water interfaces in foams, solid-gas interfaces in gas chromatography, and solid-water interfaces in cleaning systems [1]. 

Classification of wines according to the grape variety succeeds better, in general, because there are many more typical bouquet components (several hundreds) than mineral and trace elements being typical for the origin of wine. The organic compounds can be analyzed easily and reliably by Headspace Solid-Phase Microextraction Capillary Gas Chromatography and afterwards used for classification (De la Calle et al. [1998]). An example... 

So far we have discussed solvation properties at a reference temperature of 120°C. The choice of reference temperature arises from historical considerations. McReynolds chose this temperature to compile his extensive database of retention measurements for volatile solutes on a large number of stationary phases. His database has been widely used for exploring new approaches to stationary phase classification and has influenced others into using the same temperature to collect additional reference data to maintain compatibility with the original database. The choice of a standard reference temperature is of less concern than whether a single reference temperature is sufficient to classify solvent properties for use at temperatures distant from the reference temperature. There is only a limited amount of data for the influence of temperature on selectivity in gas-liquid chromatography [53,81,103,121,122]. In general polar interactions are... 

Classification of capillary columns seems to be a basic problem in gas chromatography [42-44]. Some authors believe that the terms open capillary columns with a porous layer on the inner wall surface and open capillary columns with a solid carrier layer on e inner walls are badly confused. One reason for this situation is an insufficiently strict classification of capill uy columns. We proposed a more general (in our opinion) classification based on the following criteria (1) the presence (or absence) of a porous layer on the inner capillary column walls eind (2) the presence (or absence) of a stationary liquid phase layer on the inside column walls (see Table 1-4 [45]). 

Techniques of modem electrophoresis applied to biological polymers are similar to those of modem liquid chromatography. An apparatus of modem liquid chromatography consists of three basic parts the eluent (mobile phase), the column (stationary phase), and the detector. Likewise, an apparatus of electrophoresis consists of three basic parts the electrolyte buffer, the supporting medium, and the mode of detectors. The classification of electrophoresis is in general based on the choice of the three fundamental parts, particularly the supporting medium. 

With the advent of gas chromatography the analysis of fatty acids has become a relatively routine task. As a consequence, the fatty adds of a wide variety of bacteria have been analyzed and some correlations with taxonomic classification have become clear. It should be pointed out that fatty acids, as free fatty acids, constitute only a small proportion of the lipids of both the Gram-negative and Gram-positive eubac-teria. For instance, in E. coU, Azotobacter agilis, and Agrobacterium tumefaciens, the free fatty acid content is less than 10% of the total lipid (Kaneshiro and Marr, 1961), while in Sarcina lutea it is 2.1% (Huston et al., 1965). Most analyses of die bacterial fatty adds have been performed on the total fatty adds obtained by hydrolysis of flie total hpid. Four general classes of fatty acid have been found in the eubacteria saturated and unsaturated fatty acids, and branched-chain and cyclopropane fatty adds. 

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