Empirical quantum chemical approach to structure-gas chromatographic retention index relationships (original) (raw)
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2009
Quantitative structure-property relationship (QSPR) solvent model has been developed for the McReynolds constants (prototypical solutes) on 36 gas-liquid chromatographic stationary phases. PM6 semiempirical quantum chemical calculations combined with conductor-like screening model (COSMO) has been utilized. From 276 descriptors considered, forward stepwise variable selection, followed by best subset selection, yielded linear regression models containing six purely quantum chemical and two hybrid, topologically based descriptors. Internal (leave-one-out and bootstrap) as well as external validation methods confirmed the predictive power of these structure-driven models across all 10 McReynolds constants, with 40 Kováts-index units overall root-mean-square prediction error estimate. (T. Körtvélyesi). intent of broadly representing various types of interactions: dispersion, dipole and induction interactions, donor-acceptor forces and hydrogen-bonding). The numerical value of each McReynolds constants is taken from the difference of the Kováts retention indices of the corresponding prototypical compound on a given phase I p and that on squalane I sq (the standard apolar reference), according to the general expression Eq. (1). y, z, u, s, h, i, k, l, m) (1)
Journal of Chemical Information and Modeling, 1996
Gas-liquid chromatography retention indexes for organic molecules are determined by the interaction between the molecule and the column liquid phase. In this article, a model for calculating the interaction energy between a molecule and a dielectric wall is developed. The model is at least to our knowledge the first attempt to predict retention indexes from the interaction between the molecules and the column. This approach to predict retention indexes is radically different from methods proposed before. Earlier predictions of the retention indexes have been done by a large number of descriptors, which were linearly correlated to the retention indexes. The developed model has been tested for polycyclic aromatic hydrocarbons mainly with a molecular weight of 302. For the molecules with MW 302 the obtained correlation coefficient is 0.92. A somewhat simpler model is used to fit PAH with different MWs. A correlation coefficient of 0.998 is obtained if the retention indexes were fitted to the logarithm of the interaction energies between the PAHs and the column.
Methodology for deriving quantitative structure-retention relationships in gas chromatography
Analytica Chimica Acta, 1992
Two types of models are postulated for deriving linear quantitative retention-structure models in gas chromatography (GC). They were tested by using GC retention indices for a series of 41 alkylbenzenes and 34 physico-chemical (e.g., boiling point) and calculable (topological, steric and electronic) indices. The first type of model includes a limited (optimized) set of factors. These models obey the statistical requirements and should be reliable for predictions within the interpolation and extrapolation regions of the regression model parameters and for studying the interaction mechanism between the stationary phase and analyte molecules. The second type of model does not satisfy some of the statistical criteria at the cost of an increase in model accuracy. The calculated retention values could be used for identification purposes without standard compounds.
Chromatographia, 2022
Chromatography is a separation method that utilizes differences in intermolecular interactions of the sample components with the mobile and stationary phases as the sample passes through the column. Acetic acid is a compound of focus in the study of pharmaceutical residues and short-chain fatty acids. Gas chromatography using polar capillary columns (DB-WAX) is an effective means of analyzing acetic acid. In one such solvent, dimethyl sulfoxide (DMSO), the retention time of the acetic acid shows a positive linear correlation with an equal volume increase of the DMSO solvent. We used the quantum chemistry calculation programs ORCA 5.0 and Multiwfn 3.7 with the DFT M062X/6-311 + + G(3d,2p) method to calculate the chromatographic separation parameters. We then analyzed formic acid for comparison and found the retention time of formic acid in the DB-WAX capillary column was longer than that of acetic acid. The retention time variation of formic acid in DMSO solvent compared with aqueous solvent was longer than that of acetic acid; the reason for this observation is that their retention time variation in DMSO solvent was related to the formation of strong hydrogen bonds. There are currently few studies focusing on quantum chemical calculations in chromatographic separations. Our studies using gas chromatography analysis and quantum chemical calculations explain the reasons for retention time variations.
Journal of Chromatography A, 2011
It has been demonstrated for a long time that in the particular case of gas-liquid chromatography (GLC), a linear free energy relationship (LFER) of five terms can be established, each term including a parameter of solute and a parameter of solvent. The nature of some of these parameters has been quite clearly identified, even if not always well predicted from the molecular structure. First of all, the five solute parameters: two involved in the hydrogen bonding and three in the Van der Waals forces; secondly, the two solvent parameters involved in hydrogen bonding. It was remaining an uncertainty concerning the nature of the solvent parameters named D, W and E, respectively associated with the solute parameters of dispersion, orientation and induction/polarizability. This uncertainty has been solved using experimental chromatographic data of McReynolds (56 phases) and of the Kováts group (11 phases). The parameter W appears as of polar nature strictly speaking. The parameters D and E can be expressed by two opposite bilinear functions of 1/V (inverse of molecular volume) and PSA/V (ratio of the polar surface area over the molecular volume). These results are in agreement with previous studies limited to alkanes by the Kováts group.
Simulating Retention in Gas−Liquid Chromatography
The Journal of Physical Chemistry B, 1999
Accurate predictions of retention times, retention indices, and partition constants are a long sought-after goal for theoretical studies in chromatography. Configurational-bias Monte Carlo (CBMC) simulations in the Gibbs ensemble using the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field have been carried out to obtain a microscopic picture of the partitioning of 10 alkane isomers between a helium vapor phase and a squalane liquid phase, a prototypical gas-liquid chromatography system. The alkane solutes include some topological isomers that differ only in the arrangement of their building blocks (e.g., 2,5dimethylhexane and 3,4-dimethylhexane), for which the prediction of the retention order is particularly difficult. The Kovats retention indices, a measure of the relative retention times, are calculated directly from the partition constants and are in good agreement with experimental values. The calculated Gibbs free energies of transfer for the normal alkanes conform to Martin's equation which is the basis of linear free energy relationships used in many process modeling packages. Analysis of radial distribution functions and the corresponding energy integrals does not yield evidence for specific retention structures and shows that the internal energy of solvation is not the main driving force for the separation of topological isomers in this system. 10.
New applications of the retention index concept in gas and high performance liquid chromatography
Fresenius' Journal of Analytical Chemistry, 1999
New methods for the precalculation of GC retention indices (RIs) are discussed. The first is based on a new modification of the correlation equation log RI = a logT b + bA + c and is recommended for low boiling compounds of the general type R-X with known boiling points (T b) analyzed on polymer sorbent Porapack Q. The second method permits one to predict RIs of products of organic reactions A + B → C +… with the correlation ∆RI = a ∆E + b (a < 0,|ρ| > 0.9), where ∆RI = RI C-RI A-RI B and ∆E = E C-E A-E Bare the differences in the internal molecular energies of reagents and products of organic reactions which are estimated by molecular dynamics methods. In the final section new possibilities of the use of RIs in reversed phase HPLC, namely for the determination of the number of hydroxyl groups in phenols, are illustrated.
1993
The use of theoretically calculated molecular properties as predictors for retention in reversed-phase HPLC has been explored. HPLC retention times have been measured for a series of 47 substituted aromatic molecules in three solvent mixtures and steric and electronic properties of these compounds have been derived using semi-empirical molecular orbital and empirical theoretical methods. A subset of the experimental data (a training set) was used to derive Property-retention time relationships and the remaining data were then used to test the predictive capability of the methods. Good retention time prediction was possible using derived regression equations for individual solvents and after including solvent parameters it was possible to predict retention for all solvents using a single equation. This method showed that the most useful properties were calculated log P and the calculated dipole moment of the solutes, and the calculated Solvent polarisability. In addition, 90 % of the data Were used to train an artificial neural network and the remaining 10 % of the data used to test the network; excellent prediction was obtained, the neural network approach being as successful as the regression analysis.