Fields, SM
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.
1988
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.
Fields, SM
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.
1988
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.