Turbulent Supercritical Fluid Chromatography in Open-Tubular Columns for High-Throughput Separations

A method utilizing turbulent flow to perform ultrafast separations and screen chiral compounds in supercritical fluid chromatography (SFC) is described. Carbon dioxide at high flow rates (up to 4.0 mL/min) is delivered into gas chromatography (GC) open-tubular columns (OTC, 0.18 mm i.d., 20 m long, ∼0.2 μm stationary film thickness) to establish turbulent flow at Reynolds numbers (Re) as high as 9000. Postcolumn dispersion is eliminated by using a modified UV detector that takes measurements directly on column. Upon crossing the laminar-to-turbulent flow transition regime, a significant reduction in plate height is observed resulting in a nearly 3-fold increase in peak capacity from the laminar regime. This is explained by the massive reduction of the mass transfer resistance in the mobile phase due to a flatter flow profile and faster analyte dispersion across the open-tubular column (OTC) i.d.. Demonstrated in this work is a 9 s separation of four polycyclic aromatic hydrocarbons (PAHs) over a 2.2 s separation window using a poly(dimethylsiloxane-co-methylphenylsiloxane) coated OTC. Additionally, three chiral compounds and three chiral cyclodextrin-incorporated OTCs were evaluated at high temperatures (90-120 °C) and CO₂ flow rates (3.3-3.7 mL/min) to demonstrate column stability and application of this method for rapid screening. Turbulent SFC provides a separation method for users desiring to achieve separation speeds above what is currently available with very high-pressure LC systems and do so without the resolution loss commonly observed at maximum allowable speed.