Retention In Supercritical Fluid Chromatography Research Articles

Temperature and pressure effects on solubility in supercritical carbon dioxide and retention in supercritical fluid chromatography

Solubilities of some polycyclic aromatic hydrocarbons (PAHs) in supercritical carbon dioxide were measured with a procedure based on a direct on-line combination of a saturation cell to a flame ionization detector. Acenaphthene, anthrance and chrysene were selected as the test solutes. A method was developed and evaluated which enables the measurement of the contribution of solute vapor pressure to the overall solubility. The effects of temperature and pressure on solubility in supercritical carbon dioxide were investigated and discussed in detail. The trends of solubility changes in supercritical carbon dioxide and the variations in observed retention in supercritical fluid chromatography (SFC) were correlated. Equations were derived to estimate the effects of temperature on the solute's affinity for the stationary phase in SFC.

Addition of methanol to the mobile phase in packed capillary column supercritical fluid chromatography retention mechanisms from linear solvation energy relationships

Linear solvation energy relationships (LSERs) were used to verify previously proposed retention mechanisms when an organic modifier is used with an octyldecylsilane bonded phase in packed capillary column supercritical fluid chromatography. Supercritical fluid chromatographic retention data for a wide variety of compounds at different modifier concentrations were obtained using a 60 cm×200 μm I.D. ODS packed capillary column. Supercritical carbon dioxide at a pressure of 260 atm was used as mobile phase and methanol as modifier. The LSER regression equation used was log k′ = SP 0 + llog L 16 + s π 2 H + αα 2 H + bβ 2 H + rR 2, where k′ represents the capacity factor and L 16 represents the partition coefficient of the solute between the gas phase and n-hexadecane at 298 K, and l, s, a, b and r are the regression coefficients. By increasing the percentage of modifier added to the mobile phase, the l coefficient decreased gradually. The b and s coefficients were greatly decreased on moving from neat carbon dioxide mobile phase to 2% methanol modifier, thereafter showing a gradual decrease with increasing modifier concentration. From these observations, we substantiate the conclusion that when a small amount of modifier (up to 2%) is added, the predominent modifier effect on the ODS bonded phase is dynamic coating of free silanols on the surface of the stationary phase, and when more modifier is added, another effect, i.e. an increase in the density of the mobile phase leading to an increase in elution strength of the eluent, becomes more important.

Retention in SFC at high density

AbstractThe elucidation of the detailed mechanism of retention in supercritical fluid chromatography (SFC) is a complex problem, especially for high‐density supercritical fluid mobile phases. Martire and Boehm developed a theory of SFC retention based on a statistical thermodynamic treatment, and introduced a density‐squared equation for retention in SFC: In k = a + b/T + cρ + dρ/T + eρ2/T. In this paper the systems n‐alkane‐polydimethylsiloxane‐CO2 and n‐carboxylic acid methyl ester‐polydimethylsiloxane‐CO2 have been treated using the method introduced by Martire and Boehm. In the ranges of reduced temperature from 1.079 to 1.293 and reduced SF mobile phase density from 0.705 to 1.632, two problems were discovered in the treatment of SFC retention behavior by the method of Martire and Boehm: (1) the experimental value of the site of CO2 in the lattice field, ra, of the two systems was ca 0.9, which is obviously different from the theoretical values of 3.6 or 5.4; and (2) the difference between experimental and calculated retention values increased with increasing SF mobile phase density. The minimum in SFC retention predicted by Martire and Boehm was not observed. On the basis of some assumptions and the experimental data, the following retention equation was derived: In k = a + b/T + cρ + dρ/T + eρ2/T + fρ3/T + gρ4/T. This equation was consistent with the experimental data and can conveniently be used to explain other SFC retention behavior.

Rapid Analysis of Polymethoxylated Flavones from Citrus Oils by Supercritical Fluid Chromatography

The analysis of citrus essential oils for their content of polymethoxylated flavones (PMFs) using packed column supercritical fluid chromatography (SFC) is described. Samples of sweet orange and mandarin oil were quantitatively analyzed and the resulting flavone levels compared to the values obtained using liquid chromatography. In addition, milligram quantities of all six individual flavone compounds were isolated from a sample of sweet orange oil. Flavone retention in SFC is explained on the basis of substituent dipolarity. Dipoles were calculated using molecular modeling techniques, and the effects of substituent positions or neighboring dipoles were investigated. It is postulated that steric hindrance plays a role in the retention mechanism.

Prediction of the Solubility in Supercritical Fluids Based on Supercritical Fluid Chromatography Retention Times

An improved method for the rapid prediction of solubilities of solutes in supercritical fluids is proposed. The method is based on the measured retention times of solutes eluting from packed and capillary supercritical fluid chromatography (SFC) columns. The solubilities in CO2 of four polycyclic aromatic hydrocarbons were estimated with an average error of about ±30% using retention data obtained by packed column SFC. For more polar compounds, which may interact strongly with the stationary phase in packed columns, capillary column SFC gave better results. Agreement to better than 35% was found between the solubilities obtained by this method and those obtained gravimetrically for compounds with a variety of functionalities. Several factors have been investigated, including the relationship between solubility and the reciprocal of the capacity factor, the effect of temperature, and the effect of the stationary phase.

Thermodynamic pitfalls in chromatography revisited: Supercritical fluid chromatography

Relationships between solute retention in supercritical fluid chromatography and thermodynamic properties of solute transfer from the mobile to the stationary phase are reviewed and illustrated with statistical thermodynamic calculations on a model system. Attention is paid to the effect of sorption of the mobile phase fluid into the stationary phase. The nearly linear plots of ln k′ vs. 1/ T at a constant density of the mobile phase fluid (“Van 't Hoff plots”) are shown to be of little use in themselves for determining the solute transfer properties. Apparent linearity of these plots results from cancellation of thermodynamic anomalies near the critical point of the mobile phase fluid.

Statistical thermodynamic treatment of high-pressure phase equilibria in supercritical fluid chromatography. 1. Theory

The classical thermodynamics relationships for the pressure and temperature derivatives of solute retention in supercritical fluid chromatography (SFC) contain composition terms resulting from the effect of sorption of the mobile-phase fluid into the stationary phase («swelling»). In this paper, the random-mixing version of the Panayiotou-Vera lattice model has been employed to expressed the complicated effect of swelling on solute retention in terms of molecular parameters. The present treatment takes into account the pressure- or temperature-induced changes in both volume and composition of the stationary phase.

Molecular theory of chromatography for blocklike solutes in isotropic stationary phases and its application to supercritical fluid chromatographic retention of PAHs

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular theory of chromatography for blocklike solutes in isotropic stationary phases and its application to supercritical fluid chromatographic retention of PAHsChao Yan and Daniel E. MartireCite this: J. Phys. Chem. 1992, 96, 19, 7510–7517Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://doi.org/10.1021/j100198a009RIGHTS & PERMISSIONSArticle Views61Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (752 KB) Get e-Alerts

Characterization of a supercritical fluid chromatographic retention process with a large pressure drop by the temporal average density

The characterization of supercritical fluid chromatographic retention by different forms of the average density, viz., the temporal average density, the spatial average density and the arithmetic average density, is investigated in a system with appreciable pressure drop along the column. The logarithm of the capacity factor, when described in terms of the temporal average density, is independent of the pressure drop. Hence, supercritical fluid chromatographic retention processes can be characterized and represented by a hypothetical zero-pressure-drop system at a density equal to the temporal average density of the real system.

Determination and theoretical analysis of supercritical fluid chromatographic retention of polycyclic aromatic hydrocarbons in a polymeric smectic phase

A molecular theory of chromatography based on a mean-field lattice model has recently been developed to describe the partitioning or blocklike molecules between an isotropic mobile phase and an anisotropic stationary phase. A carefully designed capillary SFC experiment mimickung the theoretical model has been carried out. The retention behavior for PAH solutes with a smectic liquid-crystalline stationary phase and a supercritical fluid CO 2 mobile phase has been determined over a wide range or temperature and density.

Supercritical Fluid Chromatographic Retention of Anilines with Pure and Modified Fluids on Standard and Deactivated Columns

Supercritical Fluid Chromatographic Retention of Anilines with Pure and Modified Fluids on Standard and Deactivated Columns

Factors governing the analytical supercritical fluid extraction and supercritical fluid chromatographic retention of polycyclic aromatic hydrocarbons

The molecular connectivity of polycyclic aromatic hydrocarbons (PAHs) correlates well with retention data for several supercritical fluid chromatographic systems. The quantitative effect of microextractor cell geometry on supercritical fluid extraction (SFE) efficiencies of PAHs from octadecyl-bonded sorbents is compared with that seen upon varying the fluid density for the same system. Relative recoveries were increased by up to a factor of two, for coronene, by employing short broad extraction vessels, 1:1 length:I.D., compared to using long narrow vessels, 20:1 length:I.D. The average relative recovery increase was 121% with a large dependence on compound type, increasing ca. linearly with fused ring number for the PAHs studied. A similar relative recoveries increase was achievable by increasing the fluid density by 0.12 g ml −1 with a small dependence on the compound type (decreasing linearly with fused ring number).

Relationship between solute retention in supercritical fluid chromatography and fluctuation integrals in dilute supercritical mixtures

Links are revealed between certain molecular quantities in dilute, binary supercritical mixtures and the solute retention in supercritical fluid chromatography (SFC). Use is made of the fact that the isothermal compressibility of the mobile-phase fluid and the infinite-dilution partial molar volume of the solute may be expressed in terms of correlation and fluctuation integrals

Sorption isotherms in supercritical fluid chromatography

The continued and growing interest in supercritical fluid chromatography (SFC) has given rise to a need for a better understanding of the solute retention mechanism. One facet of research has aimed at a theoretical description of solute retention using equation of state models based on statistical mechanics and thermodynamic descriptions of the P, V, T relationship for a fluid. A second approach has involved studies of the physico-chemical interaction of the supercritical fluid with the solute molecule and the stationary phase. Solute retention in SFC has been demonstrated to be a dynamic process of intermolecular interactions between the solute and the fluid mobile phase and between the solute and the bonded polymetric stationary phase. This qualitative statement is supported by spectroscopic studies of solvent cluster formation about a solute molecule in a supercritical fluid, partial molar volume studies and isotherm measurements of the fluid in different stationary phases under various conditions in SFC. Progress made to date in determining the sorption isotherms of mobile phase components in SFC is reviewed.

Solute retention in supercritical fluid chromatography as a function of pressure: A thermodynamic analysis

The pressure dependence of the solute retention in a hypothetical, isothermal, isobaric, chromatographic column is discussed in terms of the thermodynamic properties involved. In general, the logarithm of the solute capacity ratio decreases with increasing pressure along an S-shaped curve. To a first approximation, the point of inflection occurs at the pressure corresponding to the maximum compressibility of the mobile-phase fluid at the column temperature. The occurrence of a high-pressure minimum in retention at a constant temperature of the column is possible but unlikely to be observed within the practical range of operating pressure in supercritical fluid chromatography (SFC. The pressure course of the solute retention in SFC is compared with the pressure dependence of the solute solubility in pure solid-supercritical fluid phase equilibria. The sorption of the mobile phase into the stationary phase is shown to be a significant source of uncertainty in the thermodynamic interpretation of the solute retention in SFC.

Thermodynamics of retention in supercritical fluid chromatography: a refined model

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermodynamics of retention in supercritical fluid chromatography: a refined modelMichal. RothCite this: J. Phys. Chem. 1990, 94, 10, 4309–4314Publication Date (Print):May 1, 1990Publication History Published online1 May 2002Published inissue 1 May 1990https://doi.org/10.1021/j100373a079RIGHTS & PERMISSIONSArticle Views73Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (786 KB) Get e-Alerts

Retention in supercritical fluid chromatography: influence of the partial molar volume of the solute in the stationary phase

Theoretical models for retention in supercritical fluid chromatography have described solute retention based on statistical thermodynamics or classical thermodynamic models of mobile-phase interactions with the solute. The shortcomings of these models largely reside in the assumption of pressure-independent solute-stationary phase interactions with supercritical fluids. The pressure dependence of the partial molar volume of the solute in the stationary phase and the role of the partial molar volume of the solute in the stationary phase on retention in supercritical fluid chromatography are discussed based upon experimental studies with CO/sub 2/ over a wide range of fluid pressures.

Effect of the partial molar volume of the solute in the stationary phase on retention in supercritical fluid chromatography

Retention in supercritical fluid chromatography is a dynamic mechanism, involving intermolecular interactions in the mobile and stationary phases. A simple thermodynamic model, describing solute retention, has been investigated on the basis of macroscopic thermodynamic variables of the solute partial molar volume in the stationary and mobile phases. Solute-solvent interactions in the mobile phase are dominant at lower pressures. Solute-stationary phase interactions have an important role in solute retention in capillary supercritical fluid chromatography. The interaction of the solute with the five different stationary phases reflects the polarizability differences between these phases, as shown by the partial molar volume of the solute in the stationary phase.

Studies of the temperature dependence of retention in supercritical fluid chromatography

The capacity factors for the chromatographic retention of naphthalene, fluorene, phenanthrene and pyrene in supercritical carbon dioxide using an octadecyl silate bonded-phase column have been measured between 300 and 400 K. The results, which go through a maximum as a function of temperature, are quantitatively explained using the Peng–Robinson equation of state to calculate fugacity coefficients in the supercritical phase. Values of the enthalpies of solution of the compounds in the stationary phase from the vapour phase are obtained which are approximately equal and opposite to published values of the enthalpies of sublimation of the compounds.

Increasing extraction efficiency in supercritical fluid extraction from complex matrices Predicting extraction efficiency of diuron and linuron in supercritical fluid extraction using supercritical fluid chromatographic retention

Supercritical fluid extraction (SFE) conditions have been investigated in terms of mobile phase modifier, pressure, temperature and flow-rate to improve extraction efficiency. Extraction efficiencies of up to 100% in less than 2 h have been obtained. These extraction efficiencies resulted from our extensive parameter optimization experiments. Packed column supercritical fluid chromatography (SFC) has been used to examine the effect of these parameters on retention behavior. A relationship between chromatographic retention and extraction efficiency was sought. By determining trends of the chromatographic capacity factors using SFC conditions corresponding to SFE parameters, a prediction of extraction efficiency can be made. These predictions have shortened method development time in SFE.