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Hernandez-Baez DM, Reid A, Chapoy A, Tohidi B. Determination of distribution factors for heavy n-alkanes (nC 12-nC 98) in high temperature gas chromatography. J Chromatogr A 2019; 1591:138-146. [PMID: 30686646 DOI: 10.1016/j.chroma.2019.01.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Revised: 12/03/2018] [Accepted: 01/11/2019] [Indexed: 11/30/2022]
Abstract
The ultimate purpose of this research work is to get an insight into the incomplete elution of heavy n-alkanes which along with thermal cracking, is one of the two main factors questioning the reliability of High Temperature Gas Chromatography (HTGC) analysis of heavy oils. For this purpose, knowledge of how the Distribution Factors vary with temperature is an essential requirement in the GC modelling. This study provides an extension of the data set of distribution factors for n-alkanes up to nC98H198 in a HT5 GC column over the temperature range 10 °C-430 °C, and introduces a method to determine the distribution coefficient of heavy n-alkanes by using two complimentary HTGC modes: i.) High-Efficiency mode, for efficient resolution with a long column operated at low flow rate with n-alkanes elution rate up to nC64, and ii.) true SimDist mode, with a short column operated at high flow rate for inefficient resolution with n-alkanes elution rate up to nC100. Furthermore, this study demonstrates the use of the in-house obtained distribution factors as the main input in the in-house GC model for the prediction of the retention times. Its validation has been carried out using distribution factors obtained at both constant flow rate and constant inlet pressure operating conditions, with an average relative error in the GC modelling at the same operating conditions of 4.4% for the former and 1.5% for the latter. This new extension of the data set of heavy n-alkanes distribution factors provides the basis for studying the partitioning and incomplete elution of heavy n-alkanes in HTGC analysis. Also, these new distribution factors can be used as input in GC modelling, to determine the optimum analytical conditions to improve the separation process and thus the HTGC practices.
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Affiliation(s)
- Diana M Hernandez-Baez
- Hydrates, Flow Assurance & Phase Equilibria Group, Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, Scotland, EH14 4AS, UK.
| | - Alastair Reid
- Hydrates, Flow Assurance & Phase Equilibria Group, Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, Scotland, EH14 4AS, UK
| | - Antonin Chapoy
- Hydrates, Flow Assurance & Phase Equilibria Group, Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, Scotland, EH14 4AS, UK.
| | - Bahman Tohidi
- Hydrates, Flow Assurance & Phase Equilibria Group, Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, Scotland, EH14 4AS, UK
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2
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Nabi D, Gros J, Dimitriou-Christidis P, Arey JS. Mapping environmental partitioning properties of nonpolar complex mixtures by use of GC × GC. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:6814-6826. [PMID: 24901063 DOI: 10.1021/es501674p] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Comprehensive two-dimensional gas chromatography (GC × GC) is effective for separating and quantifying nonpolar organic chemicals in complex mixtures. Here we present a model to estimate 11 environmental partitioning properties for nonpolar analytes based on GC × GC chromatogram retention time information. The considered partitioning properties span several phases including pure liquid, air, water, octanol, hexadecane, particle natural organic matter, dissolved organic matter, and organism lipids. The model training set and test sets are based on a literature compilation of 648 individual experimental partitioning property data. For a test set of 50 nonpolar environmental contaminants, predicted partition coefficients exhibit root-mean-squared errors ranging from 0.19 to 0.48 log unit, outperforming Abraham-type solvation models for the same chemical set. The approach is applicable to nonpolar organic chemicals containing C, H, F, Cl, Br, and I, having boiling points ≤402 °C. The presented model is calibrated, easy to apply, and requires the user only to identify a small set of known analytes that adapt the model to the GC × GC instrument program. The analyst can thus map partitioning property estimates onto GC × GC chromatograms of complex mixtures. For example, analyzed nonpolar chemicals can be screened for long-range transport potential, aquatic bioaccumulation potential, arctic contamination potential, and other characteristic partitioning behaviors.
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Affiliation(s)
- Deedar Nabi
- Environmental Chemistry Modeling Laboratory, GR C2 544, Swiss Federal Institute of Technology at Lausanne (EPFL) , Station 2, CH-1015 Lausanne, Switzerland
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Bicchi C, Blumberg LM, Rubiolo P, Cagliero C. General retention parameters of chiral analytes in cyclodextrin gas chromatographic columns. J Chromatogr A 2014; 1340:121-7. [DOI: 10.1016/j.chroma.2014.03.027] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 03/06/2014] [Accepted: 03/10/2014] [Indexed: 10/25/2022]
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Wu L, Chen Y, Caccamise SA, Li QX. Difference equation model for isothermal gas chromatography expresses retention behavior of homologues of n-alkanes excluding the influence of holdup time. J Chromatogr A 2012; 1260:215-23. [PMID: 22939376 PMCID: PMC3587695 DOI: 10.1016/j.chroma.2012.07.077] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 07/25/2012] [Accepted: 07/26/2012] [Indexed: 12/01/2022]
Abstract
A difference equation (DE) model is developed using the methylene retention increment (Δtz) of n-alkanes to avoid the influence of gas holdup time (tM). The effects of the equation orders (1st-5th) on the accuracy of a curve fitting show that a linear equation (LE) is less satisfactory and it is not necessary to use a complicated cubic or higher order equation. The relationship between the logarithm of Δtz and the carbon number (z) of the n-alkanes under isothermal conditions closely follows the quadratic equation for C3-C30n-alkanes at column temperatures of 24-260 °C. The first and second order forward differences of the expression (Δlog Δtz and Δ2log Δtz, respectively) are linear and constant, respectively, which validates the DE model. This DE model lays a necessary foundation for further developing a retention model to accurately describe the relationship between the adjusted retention time and z of n-alkanes.
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Affiliation(s)
- Liejun Wu
- Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA
| | - Yongli Chen
- College of Natural and Computational Sciences, Hawaii Pacific University, 45-045 Kamehameha Highway, Kaneohe, HI 96744, USA
| | - Sarah A.L. Caccamise
- Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA
| | - Qing X. Li
- Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA
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Influence of carrier gas on the prediction of gas chromatographic retention times based on thermodynamic parameters. J Chromatogr A 2011; 1218:3241-6. [DOI: 10.1016/j.chroma.2010.09.068] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 09/21/2010] [Accepted: 09/23/2010] [Indexed: 11/21/2022]
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6
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Karolat B, Harynuk J. Prediction of gas chromatographic retention time via an additive thermodynamic model. J Chromatogr A 2010; 1217:4862-7. [DOI: 10.1016/j.chroma.2010.05.037] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 05/17/2010] [Accepted: 05/19/2010] [Indexed: 12/01/2022]
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7
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Jalan A, Ashcraft RW, West RH, Green WH. Predicting solvation energies for kinetic modeling. ACTA ACUST UNITED AC 2010. [DOI: 10.1039/b811056p] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Moretti P, Vezzani S, Castello G. A calculation method for the prediction of effective plate height in capillary gas chromatography. J Chromatogr A 2009; 1216:8986-91. [DOI: 10.1016/j.chroma.2009.10.059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2009] [Revised: 10/22/2009] [Accepted: 10/23/2009] [Indexed: 11/25/2022]
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Aldaeus F, Thewalim Y, Colmsjö A. Prediction of retention times and peak widths in temperature-programmed gas chromatography using the finite element method. J Chromatogr A 2009; 1216:134-9. [DOI: 10.1016/j.chroma.2008.11.038] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2007] [Revised: 11/07/2008] [Accepted: 11/13/2008] [Indexed: 10/21/2022]
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Aldaeus F, Thewalim Y, Colmsjö A. Prediction of retention times of polycyclic aromatic hydrocarbons and n-alkanes in temperature-programmed gas chromatography. Anal Bioanal Chem 2007; 389:941-50. [PMID: 17851653 DOI: 10.1007/s00216-007-1528-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2007] [Revised: 07/22/2007] [Accepted: 07/26/2007] [Indexed: 10/22/2022]
Abstract
We have developed an iterative procedure for predicting the retention times of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes during separations by temperature-programmed gas chromatography. The procedure is based on estimates of two thermodynamic properties for each analyte (the differences in enthalpy and entropy associated with movements between the stationary and mobile phases) derived from data acquired experimentally in separations under isothermal conditions at temperatures spanning the range covered by the temperature programs in ten-degree increments. The columns used for this purpose were capillary columns containing polydimethylsiloxane-based stationary phases with three degrees of phenyl substitution (0%, 5%, and 50%). Predicted values were mostly within 1% of experimentally determined values, implying that the method is stable and precise.
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Affiliation(s)
- Fredrik Aldaeus
- Department of Analytical Chemistry, Stockholm University, 106 91 Stockholm, Sweden
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Hoskovec M, Grygarová D, Cvaeka J, Streinz L, Zima J, Verevkin SP, Koutek B. Determining the vapour pressures of plant volatiles from gas chromatographic retention data. J Chromatogr A 2005; 1083:161-72. [PMID: 16078703 DOI: 10.1016/j.chroma.2005.06.006] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The frequently used vapour pressure versus Kováts retention index relationship has been evaluated in terms of its universal applicability, highlighting the problems associated with predicting the vapour pressures of structurally divergent organic compounds from experimentally measured isothermal Kováts retention indices. Two models differing in approximations adopted to express the activity coefficient ratio have been evaluated using 32 plant volatiles of different structural types as a test set. The validity of these models was established by checking their ability to reproduce 22 vapour pressures known from independent measurements. Results of the comparison demonstrated that (i) the original model, based on the assumption of equal activity coefficients for the test and reference substances, led, as expected, to a poor correlation (r2 = 89.1% only), with significantly deviating polar compounds and (ii) the model showed significant improvement after incorporating a new empirical term related to vaporization entropy and boiling point. The addition of this term allowed more than 99% of the vapour pressure variance to be accounted for. The proposed model compares favourably with existing correlations, while having an added advantage of providing a convenient tool for vapour pressure determination of chemically divergent chemicals.
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Affiliation(s)
- Michal Hoskovec
- Department of Natural Products, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-166 10 Prague 6, Czech Republic
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Görgenyi M, Héberger K. Solvation enthalpies and heat capacities ofn-alkanes in four polymer phases by capillary gas chromatography. J Sep Sci 2005; 28:506-12. [PMID: 15881079 DOI: 10.1002/jssc.200301849] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Molar solvation enthalpy (deltasol H(o)298) and molar heat capacity changes (deltasol C(o)p) were determined by gas chromatography for the C6-C12 n-alkanes on four preferred stationary phases (100% polydimethyl siloxane, 50% diphenyl-50% dimethyl polysiloxane, 50% trifluoropropyl methylsiloxane, and polyethylene glycol) in commercial FSOT. Statistical evaluation indicated the temperature independence of deltasol C(o)p in the range 303-393 K. Deltasol H(o)298 depends linearly on the number of carbon atoms in the n-alkanes, but no linearity could be established for deltasol C(o)p of higher homologues on polar columns, which may be due to a more ordered state on the liquid phase. The homologues for which a linear temperature dependence exists demonstrated that deltasol C(o)p is related linearly to the van der Waals volume and the temperature derivative of the density of the stationary phase. The results are consistent with a simple physical explanation at the molecular level.
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Affiliation(s)
- Miklós Görgenyi
- Institute of Physical Chemistry, University of Szeged, H-6701 Szeged, PO Box 105, Hungary.
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Abstract
The potentiality of capillary gas chromatography (GC) as a means for research on solubility phenomena is focused. Basic thermodynamic information can be obtained in a simple and direct way from this technique relying on few parameters with their associated errors tightly controlled. An unexplored field of solvation phenomenology inaccessible to other techniques is revealed by the accuracy of capillary GC, provided that relevant chromatographic variables are utilized and an adequate treatment of the experimental information performed. The present article reviews different approaches for the attainment of basic thermodynamic information through capillary GC. Some traditional concepts on the treatment of chromatographic data for physicochemical measurement are questioned. Applications of the technique to research on solubility phenomena are depicted.
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Affiliation(s)
- Francisco Rex González
- Div. Química Analítica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 y 115, 1900 La Plata, Argentina.
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González FR, Pérez-Parajón J. Effects of solvent density on retention in gas-liquid chromatography. II. Polar solutes in poly(ethylene glycol) stationary phases. J Chromatogr A 2003; 989:265-76. [PMID: 12650259 DOI: 10.1016/s0021-9673(03)00085-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Effects of solvent density on the solubility of polar probes which undergo specific interactions with poly(oxyethylene) are studied. The analysis of retention data on capillary columns coated with oligomeric poly(oxyethylene) stationary phases shows that, within the experimental error, the enthalpic contribution to the solubility is practically independent of variations in the solvent density. Average values of enthalpies of solute transfer are reported for different probes and temperatures. The observed systematic decrease of solubility with the increasing density is due to a change of entropy. Some thermodynamic consequences inferred from these general results are discussed. One relevant observation is that the influence of solvent's final groups must be negligible. This is even the case for oligomers with number-average degrees of polymerization as low as 13, hosting solutes capable of strong interactions with the end hydroxyl groups of linear poly(ethylene glycols). Possible explanations for this behavior are explored through molecular dynamics simulations of the liquid solvent.
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Affiliation(s)
- F R González
- Instituto de Química-Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain.
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González FR, Pérez-Parajón J, García-Domínguez JA. Effects of solvent density on retention in gas-liquid chromatography. I. Alkanes solutes in polyethylene glycol stationary phases. J Chromatogr A 2002; 953:151-63. [PMID: 12058929 DOI: 10.1016/s0021-9673(02)00162-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Gas-liquid chromatographic columns were prepared coating silica capillaries with poly(oxyethylene) polymers of different molecular mass distributions, in the range of low number-average molar masses, where the density still varies significantly. A novel, high-temperature, rapid evaporation method was developed and applied to the static coating of the low-molecular-mass stationary phases. The analysis of alkanes retention data from these columns reveals that the dependence of the partition coefficient with the solvent macroscopic density is mainly due to a variation of entropy. Enthalpies of solute transfer contribute poorly to the observed variations of retention. Since the alkanes solubility diminishes with the increasing solvent density, and this variation is weakly dependent with temperature, it is concluded that the decrease of free-volume in the liquid is responsible for this behavior.
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Affiliation(s)
- F R González
- Instituto de Química-Física Rocasolano, CSIC, Madrid, Spain.
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