Instrument modifications that produced reduced plate heights <2 with sub-2 μm particles and 95% of theoretical efficiency at k = 2 in supercritical fluid chromatography

• Modifications of a “standard” SFC with commercially available parts allows full theoretical efficiency, hr < 2dp, of sub-2 μm particles in SFC for the first time.
• The definition of “ultra high performance” SFC should be peak fidelity >0.95 with k = /<2.
• No efficiency losses due to thermal gradients were observed.
• There appears to be NO incentive for using 2.1 mm ID columns to avoid thermal gradients in SFC and 3 mm ID columns should be preferred.
• Several other presumed causes of efficiency loss are disproven.

The concept of peak fidelity was shown to be helpful in modeling tubing and detector cell dimensions. Connection tubing and flow cell variances were modeled to determine appropriate internal ID’s, lengths, and volumes. A low dispersion plumbing configuration, based on these calculations, was assembled to replace the standard plumbing and produced the reported results. The modifications made were straightforward using commercially available parts. The full theoretical efficiency of a 3 × 100 mm column packed with 1.8 μm totally porous particles was achieved for the first time in supercritical fluid chromatography (SFC). Peak fidelity of >0.95 was maintained to below k = 2. A reduced plate height as low as 1.87 was measured. Thus, true “ultra high performance” SFC was achieved, with the results a major improvement from all previous SFC reports.Since there were no efficiency losses, none could be attributed to thermal gradients caused by the expansion of the fluid over large pressure drops, under the conditions used. Similarly, changes in diffusion coefficients caused by significant decreases in density during expansion are apparently balanced by the increase in linear velocity, keeping the ratio between the diffusion coefficient and the linear velocity a constant. Changing modifier concentration to change retention was shown to not be a significant problem. All these issues have been a concern in the past.Diffusion coefficients, and viscosity data needs to be collected at high pressures before the actual limits of SFC can be discovered.