Simulation of the effects of negative thermal gradients on separation performance of gas chromatography

• Published in: Journal of Chromatography A Vol. 1640; p. 461943
• Main Authors: Leppert, Jan, Blumberg, Leonid M., Wüst, Matthias, Boeker, Peter
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.03.2021
• Subjects: Chromatography, Gas - methods; Computer Simulation; Gas chromatography; gases; separation; Simulation; simulation models; solutes; Temperature; temperature profiles; Thermal gradient; Velocity gradient; Gas chromatography; Simulation; Velocity gradient; Thermal gradient
• ISSN: 0021-9673; 1873-3778
• DOI: 10.1016/j.chroma.2021.461943

•Model to simulate ideal basic separation (IBS) including deviations from IBS.•Adding negative gradients to IBS reduces the separation.•Negative gradients partly compensate for broad sample injection and for gas decompression. The effect of a gradient of solute velocity on the chromatographic separation of closely spaced solutes is investigated by usage of a simulation. The concept of the ideal basic separation (IBS), introduced by Blumberg, is used to determine the theoretical limit of a separation without any natural or artificial gradients of features of the chromatographic medium. The IBS is the best achievable separation and can therefore be used as a baseline to which other separations can be compared to. An addition of a negative velocity gradient cannot improve the separation of closely spaced solutes. The velocity gradient is realized by adding a temperature gradient to a GC separation. The simulation confirms this theoretical limit for a range of differently strong retained solutes. In a second part controlled deviations from IBS are used to show, that a velocity gradient can be beneficial in realistic, non-IBS. The addition of a negative velocity gradient can improve e.g. the separation of broad injected solute zones or counteract a positive gradient of the mobile phase velocity caused by gas decompression along the GC column. However, the improved separation cannot exceed that of a corresponding ideal basic separation. The resolution of broadly injected solutes can be increased by up to 45% of the corresponding IBS resolution by adding a negative velocity gradient. A positive velocity gradient due to gas decompression reduces the separation by up to 6%. The added negative velocity gradient, realized by a linear temperature gradient, can compensate this resolution loss by up to 2%.