Evaluation of solvent venting with a gas purge for the introduction of microliter sample volumes in supercritical fluid chromatography

Peak broadening and sample recovery are important considerations when working with large sample volume injections in capillary SFC. To measure possible contribution to peak broadening in the venting valve, a tee coupling was inserted between the retention gap and the column. A standard sample containing glyceryl esters was injected. Based on time variance measurements, the venting valve did not lead to measurable band broadening. Recovery was found to be dependent on the length of the retention gap, the CO2/He ratio in the purge gas, and the temperature of the retention gap. Cryofocusing was needed to increase the recoveries of volatile n‐alkanes. To increase the recoveries of glyceryl esters, an enhanced CO2/He ratio was needed.