Index retention

It is instructive to compare the shape profiles of Table 26. The smallest profiles are found for pyrene (10), benzo(t/)pyrene (11), and peiylene (12), and the largest profiles appear to be those of benz(fl)pyrene (13) and anthanthrene (15). Why is this the case Why, for example, isn t the profile of coronene (16) the largest, when this molecule has the largest number of fused rings The answer is not difficult to find. The profile D does not directly depend on the molecular size, but on interatomic 

The simple regression equation using the connectivity index % as the molecular descriptor for the smaller benzenoids is given in Table 26. To improve the regression, Radecki, Lamparczyk, and Kaliszan considered as an additional descriptor the ratio L/B of the length L and the width B of the rectangle within which the molecule 

In conclusion, we have to admit that the geometry-dependent descriptors do not lead to as good a correlation as that based on % and L/B. The reason is that /) are global molecular descriptors, while % is a local, bond additive descriptor, which apparently better reflects the structure-chromatographic retention relationship. However, the index /) can help us to clarify the question  

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Elution volume, exclusion chromatography Flow rate, column Gas/liquid volume ratio Inner column volume Interstitial (outer) volume Kovats retention indices Matrix volume Net retention volume Obstruction factor Packing uniformity factor Particle diameter Partition coefficient Partition ratio Peak asymmetry factor Peak resolution Plate height Plate number Porosity, column Pressure, column inlet Presure, column outlet Pressure drop... 

Kovats retention indices RI Mass transfer coefficient h... 

Bentone-34 has commonly been used in packed columns (138—139). The retention indices of many benzene homologues on squalane have been determined (140). Gas chromatography of C —aromatic compounds using a Ucon B550X-coated capillary column is discussed in Reference 141. A variety of other separation media have also been used, including phthaUc acids (142), Hquid crystals (143), and Werner complexes (144). Gel permeation chromatography of alkylbenzenes and the separation of the Cg aromatics treated with zeofltes ate described in References 145—148. 

Nepeta (Lamiaceae) is a genus of perennial or annual herbs found in Asia, Europe and North Africa. About 250 species of Nepeta are reported of which, 67 species are present in Iran. Some species of this genus are important medicinal plants and their extracts have been used for medicinal purposes. Aerial parts of Nepeta sintenisii Bornm. was subjected to hydrodistillation and the chemical composition of isolated essential oil has been analyzed by GC/MS method for first time. Identification of components of the volatile oil was based on retention indices relative to n-alkanes and computer matching with the Wiley275.L library, as well as by comparison of the fragmentation patterns of the mass spectra with those reported in the literature. 

Halang, W. A., Langlais, R., and Kugler, E., Cubic Spline Interpolation for the Calculation of Retention Indices in Temperature-Programmed Gas-Liquid Chromatography, Ana/. Chem. 50, 1978, 1829-1832. 

On the other hand, the analyst might not be interested in global retention indices. Indeed, by increasing the temperature for SF3, he would obtain similar retention indices as for the other two. He will then observe that the relative retention time, i.e. the retention times of the substances compared with each other, are the same for SF, and SF3 and different from SFj. Chemically, this means that SF3 has different polarity from SFj, but the same specific interactions. This is best expressed by using the correlation coefficient as the similarity measure. Indeed, rj3 = 1, indicating complete similarity, while r 2 23 much lower. Since both... 

Retention indices of five substances on three stationary phases in GLC... 

Integer programming has been applied by De Vries [3] (a short English-language description can be found in [2]) for the determination of the optimal configuration of equipment in a clinical laboratory and by De Clercq et al. [4] for the selection of optimal probes for GLC. From a data set with retention indices for 68 substances on 25 columns, sets ofp probes (substances) (p= i,2,..., 20) were selected, such that the probes allow to obtain the best characterization of the columns. This type of application would nowadays probably be carried out with genetic algorithms (see Chapter 27). 

Semperatuie proqcammlnq (computer simulation 55 optimization 53 preparative separations 211 programming rate 53 retention indices 178 theoretical models 54 Temperature programming LC 83 SFC 630... 

Relationship Between Retention Indices and Solute Properties... 

Many, if not most, pharmacologically active compounds are amines. For this reason, issues in the RPLC of substances of pharmaceutical interest tend to be similar to those encountered in the separation of amines. Incompletely endcapped silica-based phases may exhibit tailing. The use of ion pairing or ion suppression is common in the analysis of pharmacologically active substances. Also, derivatization of the amine functionality prior to analysis may be required. The RPLC retention indices of most common pharmaceutical compounds have been compiled.97... 

Kuronen, P., Identification using retention indices on gradient HPLC, in Retention and Selectivity in Liquid Chromatography, Smith, R. M., Ed., Elsevier Science, Amsterdam, 1995, chap. 6. 

Bogusz, M., Franke, J. P., de Zeeuw, R. A., and Erkens, M., An overview of the standardization of chromatographic methods for screening analysis in toxicology by means of retention indices and secondary standards. Part II. High performance liquid chromatography, Fresenius ]. Anal. Chem., 347, 73, 1993. 

In chromatography-FTIR applications, in most instances, IR spectroscopy alone cannot provide unequivocal mixture-component identification. For this reason, chromatography-FTIR results are often combined with retention indices or mass-spectral analysis to improve structure assignments. In GC-FTIR instrumentation the capillary column terminates directly at the light-pipe entrance, and the flow is returned to the GC oven to allow in-line detection by FID or MS. Recently, a multihyphenated system consisting of a GC, combined with a cryostatic interfaced FT1R spectrometer and FID detector, and a mass spectrometer, has been described [197]. Obviously, GC-FTIR-MS is a versatile complex mixture analysis technique that can provide unequivocal and unambiguous compound identification [198,199]. Actually, on-line GC-IR, with... 

MSD provides molecular weight, fragmentation information and mass selectivity. Also, simultaneous GC-MS/MIP-AES has been described, using both a low-pressure and an atmospheric-pressure splitter [336]. The combination of MS and AED data sets provides the potential for application to a wide range of analytical problems, such as screening for the presence of hetero-atom-containing analytes (AED), identification and confirmation (MS) and quantification (MS, AED). On-line LVI-GC-AED/MS (dual detection) has been described with small (i.e. less than 0.5 s) differences in retention time of a compound with AED and MS detection [67], The dual-hyphenation set-up largely eliminates data-interpretation problems caused by small differences in retention time, or retention indices and is,... 

A method where phospholipids are entrapped in the pores of resin beads, in the forms of multilamellar vesicles, has been described [313-319,376]. In some ways, the idea is similar to that of IAM chromatography, even though the resin is modified differently. The retention indices correlate very well with the partition coefficients measured in liposome-water systems (described below). 

Interpretation of measurements of methods X-ray fluorescence spectrometry (Janssen and van Espen [1986] Arnold et al. [1994]), X-ray diffraction spectra (Adler et al. [1993]), NMR spectra (HIPS, Wehrens et al. [1993a]), HPLC retention indices (RIPS, Wehrens [1994]), Karl Fischer titration (HELGA, Wunsch and Gansen [1989]). 

Dupuis F, Dijkstra A (1975) Application of information theory to analytical chemistry. Identification by retrieval of gas chromatographic retention indices. Anal Chem 47 379... 

Table 10.1 Compounds trapped by headspace SPME from different resins, gum resins and archaeological samples, presented by Increasing retention indices, with the corresponding relative peak areas (%) for each substance... 

Components are presented by increasing retention indices, with their corresponding relative peak area (%). Values in bold correspond to compounds in high level or characteristic of an... 

A retention index (RI) was used to allow comparison of compound retention data between columns of different equipment, e.g. GC and GC-MS. Straight chain hydrocarbons (alkanes) were assigned an index of 100 times the number of carbon atoms in the molecule. The RI s of all compounds within all the extracts were calculated by using the difference between the retention indices of the alkane eluting before and after that compound ... 

Fig. 15.9. Correlation between observed retention indices and octanol partition coefficients [66],...

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