Markides, KE
1991
Structural Comparison of Low-Molecular-Weight Extractable Compounds in Different Rank Coals Using Capillary Column Gas Chromatography
Chang, H.-C.K.; Bartle, K.D.; Markides, K.E. and Lee, M.L.
Advances in Coal Spectroscopy, 141-164, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1991. Funded by Gas Research Institute and ACERC.
In this chapter, results from the analysis of the low-molecular-weight organic constituents in six vitrinite-rich coals of ranks ranging from lignite to low volatile bituminous are reported. Aliphatics, neutral aromatics, nitrogen-containing aromatics, and sulfur-containing aromatics were first isolated from the coal extracts using column absorption and complexation chromatography, and then they were resolved and identified using capillary column gas chromatography coupled with sulfur- and nitrogen-selective detectors, and mass spectrometry.
1990
Multidimensional Packed Capillary Coupled to Open Tubular Column Supercritical Fluid Chromatography Using a Valve-Switching Interface
Juvancz, Z.; Payne, K.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 62, 1990. Funded by Brigham Young University.
An on-line two-dimensional supercritical fluid chromatographic system (SFC/SFC) was constructed by utilizing a rotary valve interface to provide independent flow control of the two dimensions. A cold trap was employed to refocus solutes from single or multiple fractional cuts, after being transferred to the second dimension. Improved performance, including time savings, was achieved with a packed capillary to open tubular column arrangement and two independently controlled pumps, compared to earlier reported single-pump open tubular column SFC/SFC and packed capillary column SFC/SFC systems. The packed capillary in the first dimension provided a rapid chemical class separation, while the open tubular column in the second dimension provided high resolution of closely related isomers.
Determination of Sulfur-Containing Polycyclic Aromatic Compounds in Coal Extracts Using Capillary Column Gas Chromatography with Radio Frequency Plasma Detection
Chang, H.-C.K.; Skelton, R.J. Jr.; Markides, K.E. and Lee, M.L.
Polycyclic Aromatic Compounds, 1:251-264, 1990. Funded by Gas Research Institute and ACERC.
Detailed identification of sulfur-containing polycyclic aromatic compounds (S-PAC) was accomplished for solvent extracts of five different coals. The S-PAC were isolated by ligand-exchange chromatography. Due to the great complexities of these samples, capillary gas chromatography (GC) was employed for their analysis. An element selective radio frequency plasma detector was used to provide sulfur selective detections. Gas chromatography-mass spectrometry was used to identify individual compounds in isolated sulfur fractions. Condensed thiophenic compounds were found to be the major constituents in all five S-PAC fractions. Diaryl sulfides were also detected in the high volatile bituminous Illinois #6 coal. The prevalence of various S-PAC in different coal extracts was observed as a function of their rank.
1989
A Method for the Preparation of Binary Mobile Phase Mixtures for Capillary Supercritical Fluid Chromatography
Raynie, D.E.; Fields, S.M.; Djordevic, N.M.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr., 12, 51, 1989. Funded by Gas Research Institute.
Here, we describe a simple, inexpensive method for the preparation of mixed mobile phase (especially gas + liquid mixtures) for SFC. This method does not require cryogenic freezing of the organic modifier, and vacuum is needed only for initial evacuation of the closed system. Simple calculations allow determination of the exact concentrations of mixtures transferred to the SFC pumping system, accounting for loss of CO2 (or other gaseous primary fluid) during the transfer process.
Multidimensional Open-Tubular Column Supercritical Fluid Chromatography Using a Flow-Switching Interface
Davies, I.L.; Xu, B.; Markides, K.E.; Bartle, K.D. and Lee, M.L.
J. Microcol. Sep., 2, 71, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
A multidimensional system based on capillary supercritical fluid chromatography (SFC) was constructed that utilizes a simple flow-switching interface between two open-tubular 50-mm i.d. columns. A novel solvent-venting injection technique was incorporated in the system that enables single or multiple 0.5-mL volumes to be injected into an uncoated, yet deactivated, length of capillary precolumn without flooding of the analytical column. The effectiveness of multidimensional capillary SFC (SFC-SFC) for complex mixtures is demonstrated by the analysis of polycyclic aromatic hydrocarbons (PAH) in a coal tar extract, the trace determination of a methylcarbonate pesticide and its metabolites in a bird extract, and a group-type separation of hydrocarbons in a high-boiling petroleum distillate. These examples show for the first time that capillary SFC-SFC is a complementary alternative to other multidimensional chromatographic methods involving liquid or gaseous mobile phases.
Radio Frequency Plasma Detector for Sulfur Selective Capillary Gas Chromatographic Analysis of Fossil Fuels
Skelton, R.J. Jr.; Chang, H.-C.K.; Farnsworth, P.B.; Markides, K.E. and Lee, M.L.
Anal. Chem., 61, 2292, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
Polycyclic aromatic compounds (PAC) are known to be major constituents in coal and petroleum products. Polycyclic aromatic hydrocarbons (PAH) are by far the most common PAC in these materials. However, nitrogen-, oxygen- and sulfur-containing PAC are also often found in significant quantities. Because of the widespread interest in and use of fossil fuels, detailed study of their compositions has become an important task.
1988-1986
Ultraviolet-Absorption Detector for Capillary Supercritical Fluid Chromatography with Compressible Mobile Phases
Fields, S.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 60, 802-806, 1988. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
A major emphasis on current research in capillary supercritical fluid chromatography (SFC) is concerned with the use of mixed mobile phases to expand the analytical capabilities of SFC to more polar and higher molecular weight solutes than possible with single fluid mobile phases such as CO2. The mixed mobile phases that have been studied are primarily polar organic liquids in CO2. Low percentages (less than 1 mol %) of modifiers do not appear to cause any significant change in solute retention. Higher percentages (up to 20 mol %) have been shown to produce significant retention charges.
Since mobile phase flow rates and solute quantities are low in capillary SFC, it is desirable to analyze the entire effluent. However, the high percentages of organic modifiers anticipated in mixed mobile phase studies preclude the use of a flame ionization detector due to high background levels and to baseline changes during pressure or density programming. Ultraviolet-adsorption provides a simple and inexpensive detection system for use with mixed mobile phases.
Capillary SFC analysis creates stringent demands on allowable UV-absorption cell volumes, so an optical cell was developed based on fused silica capillary tubing available for gas chromatography. Highly compressible mobile phases such as CO2 create a problem in capillary UV-absorption detection that is not present for high critical temperature, low compressibility mobile phases such as n-pentane. The compressibility of CO2 produces significant density changes in the cell during pressure or density programming which leads to refractive index changes and significant base-line drift.
These effects were reduced to acceptable levels by cooling a newly designed and constructed detector cell. The system is sensitive and useful in studies of mixed mobil phases in capillary SFC. An 8.9 mol % mixture of 2-propanol or nitromethane in CO2 produced significant decreases in retention of polar and nonpolar polycyclic aromatic compounds. The 2-propanol/CO2 mobile phase effects the elution of ovalene at moderate temperature and pressure.
Identification and Comparison of Low-Molecular-Weight Neutral Constituents in Two Different Coal Extracts
Chang, H.-C.K.; Nishioka, M.; Bartle, K.D.; Wise, S.A.; Bayona, J.M.; Markides, K.E. and Lee, M.L.
Fuel, 67, 45-48, 1988. 4 pgs. Funded by Gas Research Institute.
Determination of the chemical structural features of coals is a continuing major goal of fuel science because of the vital energy source represented by this material. Coals are now perceived to be cross-linked macromolecular networks in which are trapped lower molecular weight materials either in sites readily accessible to solvent or in 'cages' analogous to clathrates. How representative this extractable material is of the multipolymeric macromolecular structure in which it is embedded in clearly open to question. However, the generally lower molecular weights of components in solvent extracts lead to much greater ease of analysis, and such extracts may provide insights into metamorphic changes undergone by the macromolecular structure during coal formation.
A two-step pyridine and then tetrahydrofuran solvent extraction procedure at room temperature under nitrogen gas flow was used to extract two different US coals, PSOC-592 (Illinois No. 5) and PSOC-521 (Rock Springs No. 7, Wyoming). Aliphatic and aromatic hydrocarbons were separated using neutral alumina column chromatography. The aromatics were then fractionated according to the number of aromatic carbons by high performance liquid chromatography. These neutral compounds were identified by gas chromatography (g.c.) and gas chromatography/mass spectrometry. n-Alkanes (C17-C31), pristane, phythane, hopanes (17aH, 21bH), and moretanes (17bH, 21aH) were found in aliphatic fractions of both coal extracts. Low-molecular-weight (2-4 rings) polycyclic aromatic hydrocarbons (PAH) were the major compounds in the aromatic fraction of the PSOC-592 coal extract. However, pentacyclic triterpenoid-like hydroaromatic hydrocarbons were the major components in the extract of the PSOC-521 coal. A number of new compounds were identified for the first time.
Direct Coupling of Capillary Supercritical Fluid Chromatography to High Resolution Mass Spectrometry with Minimum Modification
Huang, E.C.; Jackson, B.J.; Markides, K.E. and Lee, M.L.
Chromatographia, 25, 51-54, 1988. 4 pgs. Funded by US Department of Energy and Gas Research Institute.
It is estimated that the majority of analyses by supercritical fluid chromatography (SFC) involves the use of the flame ionization detector (FID) or the UV-absorbance detector. Unfortunately, each of these detectors can only be used when the SFC mobile phase and the sample being chromatographed fill certain requirements; the FID is limited to the use of only a few supercritical mobile phases, and the UV-absorbance detector can be used only when the sample molecules contain chromophores. The demand for a universal detector for SFC has intensified as the range of applicability of the technique has expanded. Coupled chromatography/mass spectrometry systems are among the most powerful analytical instruments available today for the analysis of organic mixtures. The successful marriage of gas chromatography/mass spectrometry (GC/MS) and the considerable progress in coupling liquid chromatography with the mass spectrometer (LC/MS) have naturally led to studies of SFC/MS.
The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a frit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO2 as the charge exchange medium were obtained.
Supercritical Fluid Injection of High-Molecular-Weight Polycyclic Aromatic Compounds in Capillary Supercritical Fluid Chromatography
Jackson, W.P.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr./Chromatogr. Commun. 9, 213-217, 1986. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
One class of compounds which is particularly well-suited for analysis by capillary supercritical fluid chromatography (SFC) is the large, non-volatile polycyclic aromatic hydrocarbons (PAH). These aromatic compounds typically occur in very complex samples, particularly those samples derived from coal.
As is the case with any form of chromatography, sample introduction and detection must be optimized in capillary SFC to prevent a loss of resolution due to extra-column effects. Several modes of sample introduction into the SFC system have been reported. The most widely used and apparently most successful method appears to be valved, sample-loop liquid injection as is used in HPLC.
In this study, a sample introduction system for capillary supercritical fluid chromatography, which allows the dissolution of the sample in the supercritical mobile phase before being introduced into the column, was constructed and evaluated. Supercritical n-pentane was shown to solvate high-molecular-weight polycyclic aromatic compounds that could not be solvated using cyclic aromatic compounds that could not be solvated using typical liquid solvents. In addition, split injection of a supercritical fluid solution was bound to be more reproducible than split injections of a liquid solution. The potential of such an injection system was demonstrated, although further developments are needed in order to make the technique of practical utility.
Markides, KE
1991
Structural Comparison of Low-Molecular-Weight Extractable Compounds in Different Rank Coals Using Capillary Column Gas Chromatography
Chang, H.-C.K.; Bartle, K.D.; Markides, K.E. and Lee, M.L.
Advances in Coal Spectroscopy, 141-164, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1991. Funded by Gas Research Institute and ACERC.
In this chapter, results from the analysis of the low-molecular-weight organic constituents in six vitrinite-rich coals of ranks ranging from lignite to low volatile bituminous are reported. Aliphatics, neutral aromatics, nitrogen-containing aromatics, and sulfur-containing aromatics were first isolated from the coal extracts using column absorption and complexation chromatography, and then they were resolved and identified using capillary column gas chromatography coupled with sulfur- and nitrogen-selective detectors, and mass spectrometry.
1990
Multidimensional Packed Capillary Coupled to Open Tubular Column Supercritical Fluid Chromatography Using a Valve-Switching Interface
Juvancz, Z.; Payne, K.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 62, 1990. Funded by Brigham Young University.
An on-line two-dimensional supercritical fluid chromatographic system (SFC/SFC) was constructed by utilizing a rotary valve interface to provide independent flow control of the two dimensions. A cold trap was employed to refocus solutes from single or multiple fractional cuts, after being transferred to the second dimension. Improved performance, including time savings, was achieved with a packed capillary to open tubular column arrangement and two independently controlled pumps, compared to earlier reported single-pump open tubular column SFC/SFC and packed capillary column SFC/SFC systems. The packed capillary in the first dimension provided a rapid chemical class separation, while the open tubular column in the second dimension provided high resolution of closely related isomers.
Determination of Sulfur-Containing Polycyclic Aromatic Compounds in Coal Extracts Using Capillary Column Gas Chromatography with Radio Frequency Plasma Detection
Chang, H.-C.K.; Skelton, R.J. Jr.; Markides, K.E. and Lee, M.L.
Polycyclic Aromatic Compounds, 1:251-264, 1990. Funded by Gas Research Institute and ACERC.
Detailed identification of sulfur-containing polycyclic aromatic compounds (S-PAC) was accomplished for solvent extracts of five different coals. The S-PAC were isolated by ligand-exchange chromatography. Due to the great complexities of these samples, capillary gas chromatography (GC) was employed for their analysis. An element selective radio frequency plasma detector was used to provide sulfur selective detections. Gas chromatography-mass spectrometry was used to identify individual compounds in isolated sulfur fractions. Condensed thiophenic compounds were found to be the major constituents in all five S-PAC fractions. Diaryl sulfides were also detected in the high volatile bituminous Illinois #6 coal. The prevalence of various S-PAC in different coal extracts was observed as a function of their rank.
1989
A Method for the Preparation of Binary Mobile Phase Mixtures for Capillary Supercritical Fluid Chromatography
Raynie, D.E.; Fields, S.M.; Djordevic, N.M.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr., 12, 51, 1989. Funded by Gas Research Institute.
Here, we describe a simple, inexpensive method for the preparation of mixed mobile phase (especially gas + liquid mixtures) for SFC. This method does not require cryogenic freezing of the organic modifier, and vacuum is needed only for initial evacuation of the closed system. Simple calculations allow determination of the exact concentrations of mixtures transferred to the SFC pumping system, accounting for loss of CO2 (or other gaseous primary fluid) during the transfer process.
Multidimensional Open-Tubular Column Supercritical Fluid Chromatography Using a Flow-Switching Interface
Davies, I.L.; Xu, B.; Markides, K.E.; Bartle, K.D. and Lee, M.L.
J. Microcol. Sep., 2, 71, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
A multidimensional system based on capillary supercritical fluid chromatography (SFC) was constructed that utilizes a simple flow-switching interface between two open-tubular 50-mm i.d. columns. A novel solvent-venting injection technique was incorporated in the system that enables single or multiple 0.5-mL volumes to be injected into an uncoated, yet deactivated, length of capillary precolumn without flooding of the analytical column. The effectiveness of multidimensional capillary SFC (SFC-SFC) for complex mixtures is demonstrated by the analysis of polycyclic aromatic hydrocarbons (PAH) in a coal tar extract, the trace determination of a methylcarbonate pesticide and its metabolites in a bird extract, and a group-type separation of hydrocarbons in a high-boiling petroleum distillate. These examples show for the first time that capillary SFC-SFC is a complementary alternative to other multidimensional chromatographic methods involving liquid or gaseous mobile phases.
Radio Frequency Plasma Detector for Sulfur Selective Capillary Gas Chromatographic Analysis of Fossil Fuels
Skelton, R.J. Jr.; Chang, H.-C.K.; Farnsworth, P.B.; Markides, K.E. and Lee, M.L.
Anal. Chem., 61, 2292, 1989. Funded by Gas Research Institute and the Utah Centers of Excellence.
Polycyclic aromatic compounds (PAC) are known to be major constituents in coal and petroleum products. Polycyclic aromatic hydrocarbons (PAH) are by far the most common PAC in these materials. However, nitrogen-, oxygen- and sulfur-containing PAC are also often found in significant quantities. Because of the widespread interest in and use of fossil fuels, detailed study of their compositions has become an important task.
1988-1986
Ultraviolet-Absorption Detector for Capillary Supercritical Fluid Chromatography with Compressible Mobile Phases
Fields, S.M.; Markides, K.E. and Lee, M.L.
Analytical Chemistry, 60, 802-806, 1988. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
A major emphasis on current research in capillary supercritical fluid chromatography (SFC) is concerned with the use of mixed mobile phases to expand the analytical capabilities of SFC to more polar and higher molecular weight solutes than possible with single fluid mobile phases such as CO2. The mixed mobile phases that have been studied are primarily polar organic liquids in CO2. Low percentages (less than 1 mol %) of modifiers do not appear to cause any significant change in solute retention. Higher percentages (up to 20 mol %) have been shown to produce significant retention charges.
Since mobile phase flow rates and solute quantities are low in capillary SFC, it is desirable to analyze the entire effluent. However, the high percentages of organic modifiers anticipated in mixed mobile phase studies preclude the use of a flame ionization detector due to high background levels and to baseline changes during pressure or density programming. Ultraviolet-adsorption provides a simple and inexpensive detection system for use with mixed mobile phases.
Capillary SFC analysis creates stringent demands on allowable UV-absorption cell volumes, so an optical cell was developed based on fused silica capillary tubing available for gas chromatography. Highly compressible mobile phases such as CO2 create a problem in capillary UV-absorption detection that is not present for high critical temperature, low compressibility mobile phases such as n-pentane. The compressibility of CO2 produces significant density changes in the cell during pressure or density programming which leads to refractive index changes and significant base-line drift.
These effects were reduced to acceptable levels by cooling a newly designed and constructed detector cell. The system is sensitive and useful in studies of mixed mobil phases in capillary SFC. An 8.9 mol % mixture of 2-propanol or nitromethane in CO2 produced significant decreases in retention of polar and nonpolar polycyclic aromatic compounds. The 2-propanol/CO2 mobile phase effects the elution of ovalene at moderate temperature and pressure.
Identification and Comparison of Low-Molecular-Weight Neutral Constituents in Two Different Coal Extracts
Chang, H.-C.K.; Nishioka, M.; Bartle, K.D.; Wise, S.A.; Bayona, J.M.; Markides, K.E. and Lee, M.L.
Fuel, 67, 45-48, 1988. 4 pgs. Funded by Gas Research Institute.
Determination of the chemical structural features of coals is a continuing major goal of fuel science because of the vital energy source represented by this material. Coals are now perceived to be cross-linked macromolecular networks in which are trapped lower molecular weight materials either in sites readily accessible to solvent or in 'cages' analogous to clathrates. How representative this extractable material is of the multipolymeric macromolecular structure in which it is embedded in clearly open to question. However, the generally lower molecular weights of components in solvent extracts lead to much greater ease of analysis, and such extracts may provide insights into metamorphic changes undergone by the macromolecular structure during coal formation.
A two-step pyridine and then tetrahydrofuran solvent extraction procedure at room temperature under nitrogen gas flow was used to extract two different US coals, PSOC-592 (Illinois No. 5) and PSOC-521 (Rock Springs No. 7, Wyoming). Aliphatic and aromatic hydrocarbons were separated using neutral alumina column chromatography. The aromatics were then fractionated according to the number of aromatic carbons by high performance liquid chromatography. These neutral compounds were identified by gas chromatography (g.c.) and gas chromatography/mass spectrometry. n-Alkanes (C17-C31), pristane, phythane, hopanes (17aH, 21bH), and moretanes (17bH, 21aH) were found in aliphatic fractions of both coal extracts. Low-molecular-weight (2-4 rings) polycyclic aromatic hydrocarbons (PAH) were the major compounds in the aromatic fraction of the PSOC-592 coal extract. However, pentacyclic triterpenoid-like hydroaromatic hydrocarbons were the major components in the extract of the PSOC-521 coal. A number of new compounds were identified for the first time.
Direct Coupling of Capillary Supercritical Fluid Chromatography to High Resolution Mass Spectrometry with Minimum Modification
Huang, E.C.; Jackson, B.J.; Markides, K.E. and Lee, M.L.
Chromatographia, 25, 51-54, 1988. 4 pgs. Funded by US Department of Energy and Gas Research Institute.
It is estimated that the majority of analyses by supercritical fluid chromatography (SFC) involves the use of the flame ionization detector (FID) or the UV-absorbance detector. Unfortunately, each of these detectors can only be used when the SFC mobile phase and the sample being chromatographed fill certain requirements; the FID is limited to the use of only a few supercritical mobile phases, and the UV-absorbance detector can be used only when the sample molecules contain chromophores. The demand for a universal detector for SFC has intensified as the range of applicability of the technique has expanded. Coupled chromatography/mass spectrometry systems are among the most powerful analytical instruments available today for the analysis of organic mixtures. The successful marriage of gas chromatography/mass spectrometry (GC/MS) and the considerable progress in coupling liquid chromatography with the mass spectrometer (LC/MS) have naturally led to studies of SFC/MS.
The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a frit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO2 as the charge exchange medium were obtained.
Supercritical Fluid Injection of High-Molecular-Weight Polycyclic Aromatic Compounds in Capillary Supercritical Fluid Chromatography
Jackson, W.P.; Markides, K.E. and Lee, M.L.
J. High Resoln. Chromatogr./Chromatogr. Commun. 9, 213-217, 1986. 5 pgs. Funded by Dow Chemical Company and Gas Research Institute.
One class of compounds which is particularly well-suited for analysis by capillary supercritical fluid chromatography (SFC) is the large, non-volatile polycyclic aromatic hydrocarbons (PAH). These aromatic compounds typically occur in very complex samples, particularly those samples derived from coal.
As is the case with any form of chromatography, sample introduction and detection must be optimized in capillary SFC to prevent a loss of resolution due to extra-column effects. Several modes of sample introduction into the SFC system have been reported. The most widely used and apparently most successful method appears to be valved, sample-loop liquid injection as is used in HPLC.
In this study, a sample introduction system for capillary supercritical fluid chromatography, which allows the dissolution of the sample in the supercritical mobile phase before being introduced into the column, was constructed and evaluated. Supercritical n-pentane was shown to solvate high-molecular-weight polycyclic aromatic compounds that could not be solvated using cyclic aromatic compounds that could not be solvated using typical liquid solvents. In addition, split injection of a supercritical fluid solution was bound to be more reproducible than split injections of a liquid solution. The potential of such an injection system was demonstrated, although further developments are needed in order to make the technique of practical utility.