Columns classification schemes

A classification by chemical type is given ia Table 1. It does not attempt to be either rigorous or complete. Clearly, some materials could appear ia more than one of these classifications, eg, polyethylene waxes [9002-88 ] can be classified ia both synthetic waxes and polyolefins, and fiuorosihcones ia sihcones and fiuoropolymers. The broad classes of release materials available are given ia the chemical class column, the principal types ia the chemical subdivision column, and one or two important selections ia the specific examples column. Many commercial products are difficult to place ia any classification scheme. Some are of proprietary composition and many are mixtures. For example, metallic soaps are often used ia combination with hydrocarbon waxes to produce finely dispersed suspensions. Many products also contain formulating aids such as solvents, emulsifiers, and biocides. 

The second classification scheme is less common than the first but is found in the literature. It is based on the operating method, or the mechanism by which the sample is removed from the column, and is therefore dependent on the nature of the mobile phase. This classification, which was introduced by Tiselius21 in 1940, includes elution development, displacement development, and frontal analysis, as shown in Figure 1.2.22 In practice, only elution and to a lesser extent displacement development are commonly used. 

Module 6 (Interpretation) reflects, in the form of a Classification/Action Matrix as in figure 5,3, the changes and additions to the classification scheme as described earlier under module 4 for HCl ( permanent capacities ) the most effective action will be Selection as a sixth class of management action for HC2 ( temporary capacities ) the most obvious action would be Motivation (see section 5.4). When Exxon Chemical s new worldwide Safety Management Guidelines will have been approved, their codes will replace those listed above the columns of the Classification/Action Matrix in order to improve the communication possibilities with other databases of the company. 

Figure 21. Classification scheme for vertices in the polygon construction. The fourth column gives the tiling charge, as defined in the text.

In the classification scheme in Sec. 1.4.1, the first three entries under liquid-solid separation methods, i.e., ion-exchange, adsoiption, and sorbent extraction, all belong to column separation techniques. While in the batch approach, separations based on these principles may be performed either by static equilibration or by a column technique, online columns are invariably used in FI separations, both for convenience and efficiency. FI column separation systems based on different sorptive mechanisms do not differ strongly in the principles of system design and optimization of operational parameters. Therefore, the principles discussed in the following sections are generally applicable to the different approaches. 

A complete classification scheme is shown in Figure 1.2. Note especially the names used to describe the open tubular (OT) GC columns and the LC columns they do not conform to the guidelines just presented. However,... 

Two types of gas chromatography exist gas-liquid chromatography (GLC) and gas-solid chromatography (GSC). Other classification schemes such as GSC. GLC plus capillary gas chromatography (CGC) are outdated because nowadays GLC and GSC can be performed both in packed columns and in capillary or open tubular columns,... 

Risk failure class is the same classification scheme used with all the other safety analyses and described in detail in Chapter 5. It crosses the severity of the consequences with the probability of occurrence. Many times, this colnmn is divided into two colnmns, clearly indicating the severity and the probability of occurrence. Because FMEAs are really for reliability engineers, the probability column usually contains the actnal failnre rate of the component. 

There are many ways to classify a collection of objects. Different criteria satisfy different purposes. Mendeleev and Meyer arranged their periodic tables based on two criteria The atomic masses of the elements increased across a row and the chemical properties of the elements in a column were similar. Mendeleev is more famous than Meyer as the founder of the periodic table because he subsequently used his classification scheme to make predictions about unknown elements. His predictions were later found to be true. 

How well these selectivity groupings work, and how these similarities translate into the everyday separations of the chromatographer s work is left to the judgement of the reader. There are many separations in many laboratories that can be carried out on more than one stationary phase. The column selection used for the creation of the charts described here is rather large, and the reader will surely find at least some of the columns that he or she is commonly using. With the information provided here, the interested user can then test the described classification scheme and see how well it applies to his or her separation problem. 

The orthogonal arrangement of the disc-like molecules in the columns of and D id phases makes these phases uniaxial, while the tilted phases (Drd and Doh.d and Dt) are optically biaxial. There are two additional columnar phases labeled as and that have not yet been classified. The columnar phases were discovered before the observation of a nematic phase for disc-like molecules. Both chiral nematic phases and the re-entrant behavior have now been observed in discotics. The phase diagram and molecular structure of a typical discotic liquid crystal are shown in Fig. 1.11. Finally, it is noted that another classification scheme for the discotic mesophases has been used [1.26], which is based on the notation used for the conventional smectics. 

Some method of classifying the elements for treatment in this way is clearly essential, and we have adopted the Periodic Classification with slight alterations, devoting a whole volume to the consideration of the elements in each vertical column, as will be evident from a glance at the scheme in the Frontispiece. 

Liquid chromatographic methods may be classified according to either the mechanism by which analytes are retained on the column or the mechanism by which they are removed from it. The mechanism of retention classification is the most popular scheme, and five major retention mechanisms have been identified ... 

Now all of the BE-pairs (B,E) are generated by exhaustive combination of the valence schemes that had been elaborated for the rows/columns. Within the hierarchic classification of chemical reactions, thus the level of basis reactions is reached. Subsequently chemical elements are assigned to the rows/columns of (B,E), and finally the unused valences of the reactive centers are supplied with residues as specified by the user. 

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