High-resolution turbulent flow chromatography

The resolution power of turbulent flow chromatography using carbon dioxide as the mobile phase and coated (crosslinked methyl phenyl polysiloxane) open tube columns (OTCs) as the stationary phase was investigated under retentive conditions (0 <k< 1). The improvement in column efficiency from a laminar to a turbulent flow regime was accurately measured for small molecules (coronene and benzo[a]anthracene). This relative increase in column performance decreased from 9 to 5, 3, and to 3 with increasing the retention factor from 0 to 0.2, 0.5, and to 1.0, respectively. Despite a four to five orders of magnitude larger sample dispersion coefficient in turbulent than in laminar flow, the mass transfer in turbulent flow chromatography is still controlled and limited by the slow sample transport across the viscous layer at the column wall. The benefit of turbulent flow chromatography is then restricted to small retention factor (k< 0.2). From a practical viewpoint, turbulent flow chromatography using carbon dioxide as the mobile phase and 20 m long × 180 μm i.d. × 0.2 μm film thickness OTCs provides ultra-fast (analysis time < 10 s) and high-resolution (plate counts of 33,000) separations of weakly retained compounds (k∼0.1) at Reynolds number around 5000 (3.75 mL/min, 3000 psi back pressure).