Capillary gas chromatography of C6−C14 n-alkenes on polyphenyl ether and polyethylene glycol 4000

Three-dimensional topographic index applied to the prediction of acyclic C5–C8 alkenes Kováts retention indices on polydimethylsiloxane and squalane columns

A novel approach is described for the prediction of gas chromatographic Kováts retention indices of 150 acyclic C5-C8 alkenes on two stationary phases (polydimethylsiloxane, PDMS, and squalane, SQ). The heuristic method was used to build multiple linear regression models using descriptors calculated by MODLESLAB software and CODESSA program. The resulting quantitative structure-retention relationship (QSRR) models were well-correlated, with predictive R2 values of 0.970 and 0.958 for retention indices on PDMS and SQ columns, respectively. 1Omegap, a three-dimensional (3D) topographic index, was found to play the most important role in the description of the chromatographic retention behavior of the alkenes in these two stationary phases. Moreover, this index could completely distinguish different isomers of alkene. Therefore, it can also be extended to distinguish different isomers of other compounds so that can well describe their quantitative structure-retention relationships.

Gas chromatographic-mass spectrometric characterization of all acyclic C5-C7 alkenes from fluid catalytic cracked gasoline using polydimethylsiloxane and squalane stationary phases

Published retention indices of acyclic alkenes C5-C7 on squalane and polydimethylsiloxane as stationary phases were investigated, and reliable retention indices of alkenes from various sources were converted to separation systems used in a laboratory. Retention indices measured on available authentic commercial alkenes and on alkenic fraction of gasoline, published retention indices as well as means of GC-MS were used for verification of calculated retention indices. Retention of some gas chromatographic unseparated isomer pairs was obtained by mass spectrometric deconvolution using a specific single-ion monitoring. On the basis of these retention data, C5-C7 alkenes were identified and analyzed in the gasoline from fluid catalytic cracking. In the gasoline all 59 acyclic C5-C7 isomeric alkenes were determined at significantly different concentration levels.

Semi-empirical topological method for the prediction of the chromatographic retention of cis- and trans-alkene isomers and alkanes

A new index is proposed for the prediction of the chromatographic retention of the cis- and trans-n-alkene isomers and alkanes. This index is based on the hypothesis that the chromatographic retention of the molecule is due to the interaction of each carbon atom with the stationary phase, and consequently the index is reduced by its neighbours' steric effects. The topological values are obtained by a numerical approximation considering the general behaviour of the chromatographic retention of the compounds. The simple linear regressions between the chromatographic retention and the index proposed for all branched alkanes and also isomers of the studied straight-chain C5 and C14 alkenes (1-ene, cis- and trans-2-, 3-, 4-, 5-, 6- and 7-enes) is very good (the correlation coefficient is r = 0.9999), and the elution sequence is correct for most of them. The models have a high predictive ability, as established by cross-validation values (r2cv). Thus, this new method, different from those already existent, can be used as complementary tool for the elucidation of the molecular structure, or prediction of the chromatographic retention of the cis- and trans-alkene isomers and branched alkanes. It could be extended with success, in the future, to the other types of compounds.