Chromatographic structure

J. Toft, Tutorial Evolutionary rank analysis applied to multidetectional chromatographic structures. Chemom. Intell. Lab. Syst., 29 (1995) 189-212. 

Fig. 8,3 The 2-d structures of the 14 volatile compounds in common among lavender cultivars, reported by Kim and Lee J. Chrorn. A 982, 31-47, 2002). The compounds arc numbered in order according to their retention time on an SPB-5 column from a gas chromatograph. Structures were drawn using ChemIDPIus at the NIH website (http //chcm.sis.nlm.nih.gov/chemidplus/).

Theoretical and experimental investigations into resonance hybridization between benzo[6-Jselenophene and naphthalene in benzoselenophene-doped naphthalene systems provided evidence for two nonequivalent centers for the impurity <85Mi 213-03). Chromatographic structural analysis by adsorption on graphitized thermal carbon black was used for the determination of conformation in 2-phenylchalcogenophenes <87MI 213-02). The adsorption of selenophene on various solid phases allowed its direct observation by EXAFS <9iMC6). 

This publication proposes different terms and definitions for the most important devices and their operation modes (modulator, modulation types), processes (focusing effect, zone compression, sensitivity enhancement), and specific properties of the two-dimensional response (orthogonality, separation space, and chromatographic structure). 

Chromatographic structure The observed ordering of chemically related compounds in the plane of a comprehensive two-dimensional separation. 

The number of theoretical plates N, included in Equation (8), is a measure of column efficiency, which can be individually applied to the two columns of a GCxGC set. But in comprehensive GCxGC, the use of two columns having phases with different characteristics results in the redefinition of peak capacity, a 1 D GC efficiency concept. It also results in the introduction of two new concepts related to the separation behaviour, orthogonality and chromatographic structure, which are specific to GCxGC. These three concepts are discussed in Sections 4.2, 4.3, and 4.4, respectively. 

The presence of these characteristic trends in a GCxGC chromatogram is an advantage toward its interpretation, since the overall sample type or the existence of an atypical composition can visually be checked in an easy way. Chromatographic structures also help by reducing the number of peaks that need... 

Orthogonality and the presence of chromatographic structures are characteristics of a GCxGC separation which describe the overall use of system efficiency. These concepts, important in the analysis of very complex samples, are difficult to define and even more difficult to express numerically or to compare on a quantitative basis. However, the predictive models mentioned could also be applied in a rough calculation of the retention of the compounds possibly present in samples for a given application. Orthogonality, use of the separation space, and presence of chromatographic structures, could be estimated for several sets... 

The sample composition of plant extracts is not one of multiple homologous series, so GGxGC separations of essential oils do not exhibit the same degree of chromatographic structure widely illustrated in the GGxGC analysis of... 

The Cahn-Ingold-Prelog (CIP) rules stand as the official way to specify chirahty of molecular structures [35, 36] (see also Section 2.8), but can we measure the chirality of a chiral molecule. Can one say that one structure is more chiral than another. These questions are associated in a chemist s mind with some of the experimentally observed properties of chiral compounds. For example, the racemic mixture of one pail of specific enantiomers may be more clearly separated in a given chiral chromatographic system than the racemic mixture of another compound. Or, the difference in pharmacological properties for a particular pair of enantiomers may be greater than for another pair. Or, one chiral compound may rotate the plane of polarized light more than another. Several theoretical quantitative measures of chirality have been developed and have been reviewed elsewhere [37-40]. 

In the post-World War II years, synthesis attained a different level of sophistication partly as a result of the confluence of five stimuli (1) the formulation of detailed electronic mechanisms for the fundamental organic reactions, (2) the introduction of conformational analysis of organic structures and transition states based on stereochemical principles, (3) the development of spectroscopic and other physical methods for structural analysis, (4) the use of chromatographic methods of analysis and separation, and (5) the discovery and application of new selective chemical reagents. As a result, the period 1945 to 1960 encompassed the synthesis of such complex molecules as vitamin A (O. Isler, 1949), cortisone (R. Woodward, R. Robinson, 1951), strychnine (R. Woodward, 1954), cedrol (G. Stork, 1955), morphine (M. Gates, 1956), reserpine (R. Woodward, 1956), penicillin V (J. Sheehan, 1957), colchicine (A. Eschenmoser, 1959), and chlorophyll (R. Woodward, 1960) (page 5). ... 

The four queries were examined against a list of samples tested on Whelk CSP that constitutes our search domain. Search results are summarized in Table 4-3. Of the 616 3D structures in this database list, 370 fit at least one of the query (one sample may fit more than one query) and 335 are given as resolved according to chromatographic data or information reported in the field comment. Query 2 retrieved the largest number of compounds with a high percentage of resolved samples in the hit list. While the number of hits retrieved with Query 1 is lower, this query provided a similar proportion of resolved samples (93 %). 

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