Speed-resolution advantage of turbulent supercritical fluid chromatography in open tubular columns: II - Theoretical and experimental evidences

- Golay's plate height equation extended from laminar to turbulent flow was used.
- Performance of open tubes in turbulent regime with carbon dioxide eluent is projected.
- Significant speed-resolution benefits are expected under turbulent flow regime.
- The theoretical predictions are in good agreement with experimental dispersion data.

The potential advantage of turbulent supercritical fluid chromatography (TSFC) in open tubular columns (OTC) was evaluated on both theoretical and practical viewpoints. First, the dispersion model derived by Golay in 1958 and recently extended from laminar to turbulent flow regime is used for the predictions of the speed-resolution performance in TSFC. The average dispersion coefficient of matter in the turbulent flow regime was taken from the available experimental data over a range of Reynolds number from 2000 to 6000. Kinetic plots are built at constant pressure drop (ΔP = 4500 psi) and Schmidt number (Sc = 15) for four inner diameters (10, 30, 100, and 300 μm) of the OTC and for three retention factors (0, 1, and 10). Accordingly, in turbulent flow regime, for a Reynolds number of 4000 and a retention factor of 1 (the stationary film thickness is assumed to be negligible with respect to the OTC diameter), the theory projects that a 300 μm i.d. OTC has the same speed-resolution power (200,000 theoretical plates; 2.4 min hold-up time) as that of a 10 μm i.d. OTC operated in laminar flow regime.Secondly, the experimental plate heights of n-butylbenzene are measured in laminar and turbulent flow regimes for a 180 μm × 4.8 m fused silica capillary column using pure carbon dioxide as the mobile phase. The back pressure regulator was set at 1500 psi, the temperature was uniform at 297 K, and the flow rate was increased step-wise from 0.50 to 3.60 mL/min so that the experimental Reynolds number increases from 700 to 5400. The experiments are in good agreement with the plate heights projected in TSFC at high flow rates and with those expected at low flow rates in a laminar flow regime.