Preliminary kinetic evaluation of an immobilized polysaccharide sub-2 μm column using a low dispersion supercritical fluid chromatograph

- First evaluation of a sub-2 μm immobilized polysaccharide chiral stationary phase by SFC.
- The optimum flow rate depends on the modifier concentration.
- Relatively high efficiency with fast separations.
- Very large pressure drops are a concern.
- Pump pressures as high as 600 bar did not appear to damage the column.

The performance of a 3 × 50 mm, 1.6 μm dp column with an immobilized polysaccharide stationary phase (ChiralPak IA-U) was evaluated for efficiency, and pressure drop, with respect to flow rate and modifier concentration using supercritical fluid chromatography (SFC). This appears to be the first such report using such a column in SFC. A unique low dispersion (ultra-high performance) SFC was used for the evaluation. The minimum reduced plate height of 2.78, indicates that the maximum efficiency was similar to or better than coated polysaccharide columns. Selectivity was different from ChiralPak AD, with the same chiral selector, as reported by many others.At high flows and high methanol concentrations, pump pressures sometimes approached 600 bar. With 5% methanol, pressure vs. flow rate was non-linear suggesting turbulent flow in the connector tubing. The optimum flow rate (Fopt) at 40% methanol was ≈0.8 mL/min, where the column efficiency was highest. At 5% methanol, Fopt increased to ≈1.6 mL/min, but efficiency degraded noticeably. The differences in Fopt suggests that the solute diffusion coefficients are a strong function of modifier concentration. Several sub-1 min separations, including a 7.5 s separation, are presented.