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Gert Desmet - One of the best experts on this subject based on the ideXlab platform.

  • theoretical evaluation of the advantages and limitations of Constant pressure versus Constant Flow Rate gradient elution separation in supercritical fluid chromatography
    Journal of Chromatography A, 2013
    Co-Authors: Ruben De Pauw, Gert Desmet, Ken Broeckhoven
    Abstract:

    This study reports on the possible advantages of switching from Constant Flow (cF) based gradient elution separations to Constant pressure (cP) based ones in Supercritical fluid chromatography (SFC) by means of mathematical models. All the important parameters (e.g. viscosity) were fitted as a function of pressure and mol% methanol in CO2. It is shown that when switching towards a cP approach in SFC, a time gain of 34% at the end of a 0 to 50% methanol in CO2 gradient is expected. Actual analysis time gains depend on the point at which it is evaluated (e.g. up to 41% after the equilibration step). Due to the dependence of retention on density, cF- and cP-mode do not yield the same selectivity even if the same volumetric-based gradient program is used. Because the components experience a higher average pressure in the cP-mode, the apparent retention factor is slightly lower.

  • comparison of the quantitative performance of Constant pressure versus Constant Flow Rate gradient elution separations using concentration sensitive detectors
    Journal of Chromatography A, 2012
    Co-Authors: Matthias Verstraeten, Ken Broeckhoven, Frederic Lynen, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Pat Sandra, Gert Desmet
    Abstract:

    This contribution discusses the difference in chromatographic performance when switching from the customary employed Constant Flow Rate gradient elution mode to the recently re-introduced Constant pressure gradient elution mode. In this mode, the inlet pressure is maintained at a set value even when the mobile phase viscosity becomes lower than the maximum mobile phase viscosity encountered during the gradient program. This leads to a higher average Flow Rate compared to the Constant Flow Rate mode and results in a shorter analysis time. When both modes carry out the same mobile phase gradient program in volumetric units, normally identical selectivities are obtained. However, small deviations in selectivity are found due to the differences in pressure and viscous heating effects. These selectivity differences are of the same type as those observed when switching from HPLC to UHPLC and are inevitable when speeding up the analysis by applying a higher pressure. It was also found that, when using concentration-sensitive detectors, the Constant pressure elution mode leads to identical peak areas as the Constant Flow Rate mode. Also the linearity is maintained. In addition, the repeatability of the peak area and retention time remains the same when switching between both elution modes.

  • kinetic performance limits of Constant pressure versus Constant Flow Rate gradient elution separations part i theory
    Journal of Chromatography A, 2011
    Co-Authors: Ken Broeckhoven, Matthias Verstraeten, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Gert Desmet
    Abstract:

    Abstract We report on a first series of experiments comparing the selectivity and the kinetic performance of Constant Flow Rate and Constant pressure mode gradient elution separations. Both water–methanol and water–acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the Constant Flow Rate and the Constant pressure mode is a (small) difference in efficiency caused by the difference in average Flow Rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20–95% water–acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20–40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5–10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the Constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained.

  • kinetic performance limits of Constant pressure versus Constant Flow Rate gradient elution separations part ii experimental
    Journal of Chromatography A, 2011
    Co-Authors: Ken Broeckhoven, Matthias Verstraeten, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Gert Desmet
    Abstract:

    Abstract We report on a first series of experiments comparing the selectivity and the kinetic performance of Constant Flow Rate and Constant pressure mode gradient elution separations. Both water–methanol and water–acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the Constant Flow Rate and the Constant pressure mode is a (small) difference in efficiency caused by the difference in average Flow Rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20–95% water–acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20–40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5–10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the Constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained.

Ken Broeckhoven - One of the best experts on this subject based on the ideXlab platform.

  • theoretical evaluation of the advantages and limitations of Constant pressure versus Constant Flow Rate gradient elution separation in supercritical fluid chromatography
    Journal of Chromatography A, 2013
    Co-Authors: Ruben De Pauw, Gert Desmet, Ken Broeckhoven
    Abstract:

    This study reports on the possible advantages of switching from Constant Flow (cF) based gradient elution separations to Constant pressure (cP) based ones in Supercritical fluid chromatography (SFC) by means of mathematical models. All the important parameters (e.g. viscosity) were fitted as a function of pressure and mol% methanol in CO2. It is shown that when switching towards a cP approach in SFC, a time gain of 34% at the end of a 0 to 50% methanol in CO2 gradient is expected. Actual analysis time gains depend on the point at which it is evaluated (e.g. up to 41% after the equilibration step). Due to the dependence of retention on density, cF- and cP-mode do not yield the same selectivity even if the same volumetric-based gradient program is used. Because the components experience a higher average pressure in the cP-mode, the apparent retention factor is slightly lower.

  • comparison of the quantitative performance of Constant pressure versus Constant Flow Rate gradient elution separations using concentration sensitive detectors
    Journal of Chromatography A, 2012
    Co-Authors: Matthias Verstraeten, Ken Broeckhoven, Frederic Lynen, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Pat Sandra, Gert Desmet
    Abstract:

    This contribution discusses the difference in chromatographic performance when switching from the customary employed Constant Flow Rate gradient elution mode to the recently re-introduced Constant pressure gradient elution mode. In this mode, the inlet pressure is maintained at a set value even when the mobile phase viscosity becomes lower than the maximum mobile phase viscosity encountered during the gradient program. This leads to a higher average Flow Rate compared to the Constant Flow Rate mode and results in a shorter analysis time. When both modes carry out the same mobile phase gradient program in volumetric units, normally identical selectivities are obtained. However, small deviations in selectivity are found due to the differences in pressure and viscous heating effects. These selectivity differences are of the same type as those observed when switching from HPLC to UHPLC and are inevitable when speeding up the analysis by applying a higher pressure. It was also found that, when using concentration-sensitive detectors, the Constant pressure elution mode leads to identical peak areas as the Constant Flow Rate mode. Also the linearity is maintained. In addition, the repeatability of the peak area and retention time remains the same when switching between both elution modes.

  • kinetic performance limits of Constant pressure versus Constant Flow Rate gradient elution separations part i theory
    Journal of Chromatography A, 2011
    Co-Authors: Ken Broeckhoven, Matthias Verstraeten, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Gert Desmet
    Abstract:

    Abstract We report on a first series of experiments comparing the selectivity and the kinetic performance of Constant Flow Rate and Constant pressure mode gradient elution separations. Both water–methanol and water–acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the Constant Flow Rate and the Constant pressure mode is a (small) difference in efficiency caused by the difference in average Flow Rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20–95% water–acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20–40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5–10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the Constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained.

  • kinetic performance limits of Constant pressure versus Constant Flow Rate gradient elution separations part ii experimental
    Journal of Chromatography A, 2011
    Co-Authors: Ken Broeckhoven, Matthias Verstraeten, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Gert Desmet
    Abstract:

    Abstract We report on a first series of experiments comparing the selectivity and the kinetic performance of Constant Flow Rate and Constant pressure mode gradient elution separations. Both water–methanol and water–acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the Constant Flow Rate and the Constant pressure mode is a (small) difference in efficiency caused by the difference in average Flow Rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20–95% water–acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20–40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5–10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the Constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained.

Shaokun Jiang - One of the best experts on this subject based on the ideXlab platform.

Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical comparison of the performance of gradient elution chromatography at Constant pressure and Constant Flow Rate.
    Journal of Chromatography A, 2012
    Co-Authors: Fabrice Gritti, Georges Guiochon
    Abstract:

    Abstract The theory of gradient elution usually assumes a Constant Flow Rate. This works extends it to gradients performed under Constant pressure drop and variable Flow Rates. The peak capacity is derived under both Constant Flow Rate and Constant pressure gradient chromatography by integrating the Rate of increase of the peak capacity from the hold-up time to the end of the gradient time. Assuming that the eluent mixture is incompressible, the chromatographic system isothermal, the pressure has no effect on the retention pattern, and neglecting the contributions of the instrument to the total pressure drop and the total peak width, it is found that both modes of gradient elution chromatography are strictly equivalent, provided that the elution time of the last eluted compound and the volume gradient are kept the same in both cases.

  • The use of syringe-type pumps in liquid chromatography in order to achieve a Constant Flow-Rate
    Journal of Chromatography A, 2001
    Co-Authors: Michel Martin, Gilbert Blu, Claude Eon, Georges Guiochon
    Abstract:

    Abstract The variation of the Flow-Rate of mobile phase pumped through a chromatographic column by a screw-driven syringe-type pump is discussed. It is shown that because of the compressibility of liquids, a steady-state Flow is achieved only after a long period, which depends on the characteristics of the pump, the Flow resistance of the column and the nature of the liquid. This period is normally between 15 and 60 min if liquid pumping starts from zero pressure at a Constant piston speed. The retention times observed for compounds injected during the transitory period can be up to several times greater than those observed for the same compounds under steady-state conditions. All retention data and efficiencies measured during the transitory period are not reproducible and are meaningless. Quantitative results also are not reproducible. Instructions are given for the better use of this type of pump, which, in spite of some well-known advantages, has been found to be very difficult to use for any measurements.

Matthias Verstraeten - One of the best experts on this subject based on the ideXlab platform.

  • comparison of the quantitative performance of Constant pressure versus Constant Flow Rate gradient elution separations using concentration sensitive detectors
    Journal of Chromatography A, 2012
    Co-Authors: Matthias Verstraeten, Ken Broeckhoven, Frederic Lynen, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Pat Sandra, Gert Desmet
    Abstract:

    This contribution discusses the difference in chromatographic performance when switching from the customary employed Constant Flow Rate gradient elution mode to the recently re-introduced Constant pressure gradient elution mode. In this mode, the inlet pressure is maintained at a set value even when the mobile phase viscosity becomes lower than the maximum mobile phase viscosity encountered during the gradient program. This leads to a higher average Flow Rate compared to the Constant Flow Rate mode and results in a shorter analysis time. When both modes carry out the same mobile phase gradient program in volumetric units, normally identical selectivities are obtained. However, small deviations in selectivity are found due to the differences in pressure and viscous heating effects. These selectivity differences are of the same type as those observed when switching from HPLC to UHPLC and are inevitable when speeding up the analysis by applying a higher pressure. It was also found that, when using concentration-sensitive detectors, the Constant pressure elution mode leads to identical peak areas as the Constant Flow Rate mode. Also the linearity is maintained. In addition, the repeatability of the peak area and retention time remains the same when switching between both elution modes.

  • kinetic performance limits of Constant pressure versus Constant Flow Rate gradient elution separations part i theory
    Journal of Chromatography A, 2011
    Co-Authors: Ken Broeckhoven, Matthias Verstraeten, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Gert Desmet
    Abstract:

    Abstract We report on a first series of experiments comparing the selectivity and the kinetic performance of Constant Flow Rate and Constant pressure mode gradient elution separations. Both water–methanol and water–acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the Constant Flow Rate and the Constant pressure mode is a (small) difference in efficiency caused by the difference in average Flow Rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20–95% water–acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20–40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5–10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the Constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained.

  • kinetic performance limits of Constant pressure versus Constant Flow Rate gradient elution separations part ii experimental
    Journal of Chromatography A, 2011
    Co-Authors: Ken Broeckhoven, Matthias Verstraeten, Konstantin Choikhet, Monika Dittmann, Klaus Witt, Gert Desmet
    Abstract:

    Abstract We report on a first series of experiments comparing the selectivity and the kinetic performance of Constant Flow Rate and Constant pressure mode gradient elution separations. Both water–methanol and water–acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the Constant Flow Rate and the Constant pressure mode is a (small) difference in efficiency caused by the difference in average Flow Rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20–95% water–acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20–40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5–10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the Constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained.