Chromatographic systems classification

Fig. 1. Classification of chromatographic systems where gsc is gas—soHd chromatography glc, gas—Hquid chromatography sec, size-exclusion chromatography Isc, Hquid—soHd chromatography Uc, Hquid—Hquid chromatography iec, ion-exchange chromatography tic, thin-layer chromatography ...

In a chromatographic separation procedure the parameters of the chromatographic system (stationary phase, flow, temperature, etc.) have to be selected respectively optimized with respect to some criterion (resolution, time, etc.). In gas chromatography retention data series are published and used for the sttidy of solvent/solute interaction, prediction of the retention behaviour, activity coefficients, and other relevant information usable for optimization and classification. Several clKmometrk techniques of data anal s have been employed, e.g. PCA, numerical taxonomic methods, information theory, and j ttern recognition. 

These methods allow not only the classification and clustering of any set of chromatographic systems but also exact determination of the relationship between the characteristics (physicochemical parameters or molecular substructures) of solutes and their retention behavior. It can be further concluded that chemometry considerably... 

The choice of chromatographic system and the process concept are influenced by the classification of the separation problem into one of the three scenarios of Fig. 4.4. This chapter focuses on the influence of the chromatographic system, while the influence on the process concept is explained in Chapter 5.4. Here, it should be kept in mind that the elution order of the components is essential for the whole process and the elution order is determined by the chromatographic system. Especially if one component is in excess, as in scenarios (a) and (c) in Fig. 4.4, the use of thermodynamic effects like displacement or tag along are a special source for optimization as well as for severe errors and mistakes (Chapter 2.6). 

The previous chapter discussed the solvent and its interaction with the solute. To complete the chromatographic system the adsorbent has to be selected. As mentioned in Chapter 3.2.1 one has to distinguish between enantioselective and non-enantioselective adsorbents. Both groups of adsorbents are classified into polar, semi-polar and nonpolar adsorbents (see Tab. 4.4). This classification is based on the surface chemistry of the packing material. Interaction between mobile phase and adsorbent characterizes the phase system, which is distinguished between normal phase (NP) chromatography and reversed phase (RP) chromatography. This differentiation is historic and appointed by the ratio of the polarity of the adsorbent and the mobile phase. 

Aszalos, A. and Issaq, H. J. (1980) Thin Layer Chromatographic systems for the classification and identification of antibiotics. J. Liquid Chromatogr. 3,867-883. 

Classification criteria applied for injectors used in liquid chromatographic systems are listed in Table 1 ... 

Sensor systems are composed of the sensor, the transmitter, and the associated signal processing. The sensor measures certain quantities (e.g., voltage, current, or resistance) associated with devices in contact with the process such that the measured quantities correlate strongly with the actual controlled variable value. There are two general classifications for sensors continuous measurements and discrete measurements. Continuous measurements are, as the term implies, generally continuously available, whereas discrete measurements update at discrete times. Pressure, temperature, level, and flow sensors typically yield continuous measurements, whereas certain composition analyzers (e.g., gas chromatographs) provide discrete measurements. 

Separation of the components, or solutes, of a sample results from differences in their rates of adsorption, solution, or reaction with the mobile and stationary phases. In the light of these observations distinguishing the numerous chromatographic techniques only on the basis of specification of the physical states of the stationary and mobile phases is inadequate, and a more adequate classification of these techniques must additionally also take into account (i) the nature of the separation e.g. adsorption, and (ii) the configuration of the system e.g. columnar. Table 4.4 gives a system of classification which incorporates these considerations. 

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