Organic solutes in paraffin solvents

́fayes, Guy De; Fritz, De ́nes F.; ̈rner, Tatiana Go; Huber, Gustave; Reyff, Christophe De; ́ts, Ervin sz. Kova

doi:10.1016/s0021-9673(00)96067-9

Cited by 36 publications

(19 citation statements)

References 21 publications

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“…The standard states of the related standard chemical potential, Δμ j ,sv (cal mol -1 ), are the ideal dilute one molal solution and the ideal gas state at 1 atm. For successful extrapolation, it has been proposed to fit the Kirchhoff equation to the experimental data whereupon it is supposed that the difference of the partial molar heat capacity of the solute for the two standard states, Δ C P , j ,sv (cal mol -1 K -1 ), is independent of the temperature, T (K). The symbol R (cal mol -1 K -1 ) is for the universal gas constant.…”

Section: Theoretical Sectionmentioning

confidence: 99%

“…Saturated noncyclic hydrocarbons are the “simplest” solvents insofar that they are not able to enter specific interactions with a solute. Défayes et al have shown that there is a regularity of partition data in this solvent family . Henry coefficients have been determined by gas chromatography in a temperature range of 90−210 °C on a series of five columns prepared with pure paraffins as stationary phases and synthesized by Zeltner et al The structure of the paraffins, C z H 2 z + 2 , with carbon numbers z = 59−103, is depicted in Figure .…”

Section: Theoretical Sectionmentioning

confidence: 99%

“… Here, h j ,par is an enthalpic, solute-specific constant. However, the data set of Défayes et al (partition data on five high-molecular-weight paraffins) did not permit evaluation of both solute-specific constants. Therefore, first the entropic constant, s j ,par , has been determined by regression, and then an enthalpic constant was determined as a nonsignificant refinement.…”

Section: Theoretical Sectionmentioning

confidence: 99%

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Prediction of Activity Coefficients in Low-Molecular-Weight Paraffins from Gas Chromatographic Data

Dallos¹,

Kováts²

1999

Anal. Chem.

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It is shown that gas-liquid partition coefficients measured by gas chromatography on nonvolatile paraffin stationary phases at high temperatures allow estimation of gasliquid partition coefficients of solutes at ambient temperatures in volatile alkanes as solvents. Extrapolation to low temperatures was successful by use of the Kirchhoff equation for the description of the temperature dependence of the standard chemical potential of the solute related to its molal Henry coefficient. A new equation is proposed for the prediction of partition data in lowmolecular-weight paraffins. It was derived by using the Flory-Huggins model as a guide, and it combines theory with experiment. It is proposed to accept a combinatorial entropy term determined by experiment as a solute property. The necessary experimental information consists of a set of gas chromatographic data measured at at least four temperatures on two pure, high-molecularweight paraffins. Molal Henry coefficients extrapolated to low-molecular-weight solvents allowed calculation of activity coefficients. Predicted and measured data agreed within ( 20%. The reproducibility of activity coefficients by classical experimental methods is of the same order of magnitude.Properly designed gas liquid chromatographic experiments permit a rapid collection of accurate gas/liquid partition data at ideal dilution. 1,2 In the chromatographic column the high-molecular-weight solvent (the stationary liquid) is disposed of as a thin film on a support. Therefore, its specific surface area is high, typically of the order of some 5 m 2 g -1 (corresponding to a film thickness of 0.2 µm). Hence, already weak adsorption at the liquid/solid (liquid/support) and the gas/liquid interfaces shall influence the measurement and will result in wrong partition data. By the use of an "inactive support", adsorption at the liquid/ support interface can be eliminated. Adsorption at the liquid/gas interface is roughly proportional to the surface tension of the solvent. 3-5 It cannot be eliminated but can be reduced to a minimum by the adequate choice of solvent and by the use of highly loaded stationary phases, i.e., by reducing the specific surface area of the solvent.Partition data of a solute, j, in a given solvent, sv, as a function of temperature are best presented by calculating the corresponding standard chemical potential, ∆µ j,sv (i.e., the partial molar standard Gibbs free energy). 6Here, κ j,sv , is a partial pressure (fugacity) characterizing partition, R is the universal gas constant, T is the thermodynamic temperature, and the symbols ∆H j,sv (T) and ∆S j,sv (T) are for the partial molar enthalpy and entropy differences of the solute between the ideal gas phase and the ideal dilute solution. The relationship of eq 1 shows that the standard chemical potential difference depends both on specific enthalpic interactions between solute and solvent (attraction due to polarity, hydrogen bonding, etc.) and on the entropy. The latter also includes the so-called combinatorial entropy: contributi...

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Section: Theoretical Sectionmentioning

confidence: 99%

Section: Theoretical Sectionmentioning

confidence: 99%

Section: Theoretical Sectionmentioning

confidence: 99%

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Prediction of Activity Coefficients in Low-Molecular-Weight Paraffins from Gas Chromatographic Data

Dallos¹,

Kováts²

1999

Anal. Chem.

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“…The retention of isomeric alkanes in GLC using highmolecular-weight branched alkanes as the liquid phase is the starting point in our endeavor to contribute to the understanding of chromatography retention processes. Secondary effects, such as adsorption at the sUica-liquid interface and adsorption at the liquid film-vapor interface, are negligible in GLC separations involving solutes and liquid phase of very similar chemical nature (50,51). Currently, we are investigating the partitioning of linear and branched alka nes with 5 to 8 carbon atoms between helium and squalane (2,6,10,15,19,23-hexamethyltetracosane), a widely used liquid phase in GLC (52) and the refer ence material for the Rohrschneider-McReynolds scheme of liquid phase char acterization (53j54).…”

Section: Alkane Partitioning In a Helium/squalane Glc Systemmentioning

confidence: 99%

Exploring Multicomponent Phase Equilibria by Monte Carlo Simulations: Toward a Description of Gas-Liquid Chromatography

Martin

Siepmann

Schure

1999

ACS Symposium Series

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The calculation of retention times, retention indices, and partition constants is a long sought-after goal for theoretical studies in gas chromatography. Although advances in computational chemistry have improved our understanding of molecular interactions, little attention has been focused on chromatography, let alone calculations of retention properties. Configurational-bias Monte Carlo simulations in the Gibbs ensemble have been used to calculate single and multi-component phase diagrams for a variety of hydrocarbon systems. Transferable force fields for linear and branched alkanes have been derived from these simulations. Using calculations for helium/n-heptane/n-pentane systems, it is demonstrated that this approach yields very precise partition constants and free energies of transfer. Thereafter, the partitioning of linear and branched alkane solutes (with five to eight carbon atoms) between a squalane liquid phase and a helium vapor phase is investigated. The Kovats retention indices of the solutes are calculated directly from the partition constants.The underlying principles of chromatographic separation are inherently complex, being dictated by the interplay of the sample with the stationary phase (solid substrate and bonded phase) and the mobile phase that often contains a mixture of solvents. Thus predicting the retention characteristics of a solute molecule given only its structure and the experimental chromatographic conditions is one of the grand challenges in separation science. Many different methods for the prediction of retention data have appeared in the literature (for excellent reviews, see (1-5)). We note here that many attempts at this predictive capability have Corresponding author: siepmann@chem.umn.edu. 82

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“…1). 1–3 These branched alkanes can be used as stationary phases for GC in packed and capillary columns4 and as solvents for thermodynamic investigations of non‐specific molecular interactions 5–7. Limiting activity coefficients in volatile alkane solvents at ambient temperatures for solutes of various polarities can be predicted from GC retention data obtained with the Apolane family members at higher temperatures 8…”

Section: Introductionmentioning

confidence: 99%

Field desorption mass spectrometry of large multiply branched saturated Hydrocarbons

Gross¹,

Vékey

Dallos

2001

J. Mass Spectrom.

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Large multiply branched saturated hydrocarbons containing 67-103 carbon atoms (molecular masses 941.8-1446.8 Da) were analyzed by field desorption mass spectrometry (FD-MS) with a double-focusing mass spectrometer. FD-MS was found to have detection limits in the 100 fmol range. The FD mass spectra exhibited molecular ions of astonishingly low abundance. However, the fragment ions formed were closely related to the proposed molecular structure, allowing us to set up rules for straightforward structure elucidation of unknowns. In detail, (i) dehydrogenation, (ii) alkyl losses from molecular ions and (iii) subsequent alkene losses were observed. The influence of the electric field strength on dehydrogenation and C-C cleavages was examined by variation of the emitter potential. Additionally, ion dissociations in the ion source and in the first and second field-free regions, respectively, were compared to study the relative importance of field-induced and thermally induced processes.

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Organic solutes in paraffin solvents

Cited by 36 publications

References 21 publications

Prediction of Activity Coefficients in Low-Molecular-Weight Paraffins from Gas Chromatographic Data

Prediction of Activity Coefficients in Low-Molecular-Weight Paraffins from Gas Chromatographic Data

Exploring Multicomponent Phase Equilibria by Monte Carlo Simulations: Toward a Description of Gas-Liquid Chromatography

Field desorption mass spectrometry of large multiply branched saturated Hydrocarbons

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