Components retention indices

Musumarra et al. [44] also identified miconazole and other drugs by principal components analysis of standardized thin-layer chromatographic data in four eluent systems and of retention indexes on SE 30. The principal component analysis of standardized R values in four eluents systems ethylacetate-methanol-30% ammonia (85 10 15), cyclohexane-toluene-diethylamine (65 25 10), ethylacetate-chloroform (50 50), and acetone with plates dipped in potassium hydroxide solution, and of gas chromatographic retention indexes in SE 30 for 277 compounds provided a two principal components model that explains 82% of the total variance. The scores plot allowed identification of unknowns or restriction of the range of inquiry to very few candidates. Comparison of these candidates with those selected from another principal components model derived from thin-layer chromatographic data only allowed identification of the drug in all the examined cases. 

The phenanthrene/anthracene series is shown in Fig. 7 and the major peak in the m/z 234 trace has the retention index of retene which is generally derived from conifer wood burning. Sometimes there is a triplet of peaks in the same C4 plot due to benzonaphthothiophenes (C10H16S) which are components of some... 

The concentration data obtained from each sample analysis were expressed as fractional parts and normalized to sum to 100. The normalized data were statistically analyzed, and three principal components (A=3, Equation [1]) were calculated. The PCB constituents (varlbles) are numbered sequentially and correspond to peak 1, peak 2,. .. to peak 105. The structure and retention index of each constituent in the mixture were reported by Schwartz et al. (9). The tabular listing of the data is availedile from the present authors. 

Figure 11.5 shows the structures of some of the major components in peppermint oil. The use of the retention index system is illustrated in Figures 11.6 and 11.7 for peppermint oil run in comparison with n-alkane standards on both a weakly polar OV-5-type column and a polar carbowax column. 

Retention index. I. A number relating the adjusted retention volume of a component A to the adjusted retention volumes of normal paraffins. Each n-paraffin is arbitrarily allotted, by definition, an index of one hundred times its carbon number. The index number of component A is obtained by logarithmic interpolation. 

The molecular weight and the Kovats retention index can then be combined to aid in the identification of the component. A linear relationship exists between the molecular weight and retention index for a homologous series of compounds. The relationship varies for each class of compound thus, a clue can be obtained regarding the type of compound present which can be verified by some other technique. 

Verification requires sniffing an authentic standard to verify that the component and the standard have the same retention index and odor quality. Table G 1.8.1 shows the result obtained when sniffing the sample used in Figure Gl.8.4. 

Verification requires sniffing an authentic standard to ensure that the component and the standard have the same retention index and odor quality. 

Identification of these components was based on GC/MS and retention index information. Novel compounds were isolated by preparative capillary gas chromatography and spectroscopically identified by interpretation of infrared, nuclear magnetic resonance and mass spectra. In... 

Table II lists some furan and thiophene components substituted with sulfur at the three position on both heterocyclic rings generated in one reaction system. Also included are Kovats retention index data and references reporting the occurrence in foods or model systems.

It has been shown that gas-Hquid chromatographic methods are particularly suitable for a quantitative characterization of the polarity of solvents. In gas-liquid chromatography it is possible to determine the solvent power of the stationary liquid phase very accurately for a large number of substances [98, 99, 259, 260]. Many groups of substances exhibit a certain dependence of their relative retention parameters on the solvation characteristics of the stationary phase or of the separable components. In determining universal gas-chromatographic characteristics, the so-called retention index, I, introduced by Kovats [100], is frequently used. The elution maxima of individual members of the homologous series of n-alkanes (C H2 +2) form the fixed points of the system of retention indices. The retention index is defined by means of Eq. (7-41),... 

Using a different set of standard substances, i.e. substituting 1-butanol, pentan-2-one, and 1-nitropropane for the rather volatile ethanol, butan-2-one, and nitromethane, McReynolds developed an analogous approach [103]. Altogether, he characterized over 200 liquid stationary phases using a total of 10 probes. A statistical analysis of the McReynolds retention index matrix using the principal component analysis method has shown that only three components are necessary to reproduce the experimental data matrix [262]. The first component is related to the polarity of the liquid phase, the second depends almost solely on the solute, and the third is related to specific interactions with solute hydroxy groups [262]. 

The samples were analyzed by capillary gas chromatography and gas chromatography/mass spectrometry (GC/MS). Identifications were verified by comparing the component s mass spectmm and experimental retention index (I) with that of an authentic reference standard. The retention system proposed by Kovats (12) was utilized. When standards were not available the identifications were considered tentative. 

The introduction of GC as an analytical technique has had a profound impact on both qualitative and quantitative analysis of organic compounds. Identification of compounds by GC can be accomplished by their retention times on the column as compared to known reference standards, by inference from sample treatment prior to chromatography, " or by the concept of retention index. " The latter method and tables of retention indices " with associated conditions have been reported. " Although qualitative data and analytical techniques for identification of compounds are well-established " and relative retention data for over 600 substances also have been published, " the main utility of GC undoubtedly lies in its powerful combination of separation and quantitative capabilities. Use in quantitative analysis involves the implementation of two techniques being performed concurrently, i.e., separation of components and subsequent quantitative measurement. 

The application of this concept in chromatography requires the introduction of some extra components with previously known (postulated) retention indices [RI = /(f )] into the samples being analyzed. Their peaks form a mobile coordinate system for the recalculation of tp. data of the target analytes. Hence, the establishment of any retention index system needs the following ... 

The literature of QSRR with LSS is dominated by a specific SSD, the I ER solute parameters V, E, S, A, and B, as defined in Equation 15.2. An extraordinary amount of attention has been paid to predict retention (24,25) and to establish phase selectivity in MEKC using LSER (5, 7, 26-31). Attempts to classify and to contrast micellar phases with basis on the LSER coefficients have been pursued by many researchers (5,26,27,29). Interesting approaches comprise the classification of micellar phases by the combined use of LSER parameters and retention indexes (32), the clustering of micellar systems by principal component analysis (26), the use of LSER parameters to compose vectors for characterization of lipophilicity scales (33), and, more recently, the establishment of micellar selectivity triangles (34,35) in analogy to the solvent selectivity triangle introduced by Snyder to classify solvents and ultimately mobile phases in liquid chromatography. 

Each component was initially identified by the GC retention index and the NIST library connected to the QP-5050 mass spectrometer, as described in previous papers. (10,11) A JNM-LA400 spectrometer (Jeol, Tokyo) was employed for recording the C-NMR spectra, CDCI3 being used as a solvent. 

Lycopodium Alkaloids. Gerard and MacLean (1986) reported the analysis of Lycopodium species by GC-MS. Most of the alkaloids previously reported to occur in the species examined could also be found using the GC system. One of the exceptions was lycodiflexine, which might not be sufficiently volatile since its molecular weight (562) is well above that of the other components of the extract. Besides the alkaloids reported, other minor alkaloids could be detected by this method. The retention index of 15 alkaloids is included. 

Figure 15.1. Retention index of components of standard sample containing plasticizers of different molecular weights. 1 - dibutyl adipate, 2 - dibutyl phthalate, 3 -acetyl tributyl citrate, 4 - di-(2-ethylhexyl) adipate, 5 -di-(2-ethylhexyl) phthalate. [Data from Guisto-Norkus R Gounili G Wisniecki P Huball J A Ruven Smith S ...

Alternatively, the scanned mass spectrum may be compared with a library of reference spectra, and many spectra of derivatives have been published for this purpose. This comparison step may be done by computer or manually using a variety of suitable reference publications. The comparison, when supplemented by the GC retention index, demonstrates the true power of GC-MS for the unambiguous identification of mixture components at trace levels. The choice of derivative may be influenced by that used in specialist libraries of reference spectra, e.g. methyl esters of organic acids. 

Fragmentation of these compounds are also similar. Therefore assignment of the individual component requires additional information, linear retention index or Kovat s index and confirmation with authentic standards. Manual interpretation of the mass spectrum is some time needed, when there is no fitted matching. Isotope abundance is very useful to postulate the identity of molecule or fragment. 

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