Comparison of Static Thermal Gradient to Isothermal Conditions in Gas Chromatography Using a Stochastic Transport Model

• Published in: Analytical chemistry (Washington) Vol. 93; no. 17; pp. 6739 - 6745
• Main Authors: Avila, Samuel, Tolley, H. Dennis, Iverson, Brian D, Hawkins, Aaron R, Porter, Nathan L, Johnson, Shawn L, Lee, Edgar D, Lee, Milton L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 04.05.2021
• Subjects: Chemistry; Chromatography; Gas chromatography; Injection; Phase velocity; Retention; Separation; Simulation; Stochasticity; Temperature; Temperature gradients
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.1c00438

This paper compares static (i.e., temporally unchanging) thermal gradient gas chromatography (GC) to isothermal GC using a stochastic transport model to simulate peak characteristics for the separation of C12–C14 hydrocarbons resulting from variations in injection bandwidth. All comparisons are made using chromatographic conditions that give approximately equal analyte retention times so that the resolution and number of theoretical plates can be clearly compared between simulations. Simulations show that resolution can be significantly improved using a linear thermal gradient along the entire column length. This is mainly achieved by partially compensating for loss in resolution from the increase in mobile phase velocity, which approximates an ideal, basic separation. The slope of the linear thermal gradient required to maximize resolution is a function of the retention parameters, which are specific to each analyte pair; a single static, thermal gradient will not affect all analytes equally. A static, non-linear thermal gradient that creates constant analyte velocities at all column locations provides the largest observed gains in resolution. From the simulations performed in this study, optimized linear thermal gradient conditions are shown to improve the resolution by as much as 8.8% over comparative isothermal conditions, even with a perfect injection (i.e., zero initial bandwidth).