INVESTIGATION OF RETENTION AND SELECTIVITY IN HIGH-TEMPERATURE, HIGH-PRESSURE, OPEN-TUBULAR SUPERCRITICAL-FLUID CHROMATOGRAPHY WITH CO2 MOBILE-PHASE

We studied solute retention for n-hydrocarbons, (low-molecular-weight) polystyrenes, an ethoxylated surfactant, and a selectivity test mix o n open-tubular columns with methyl-, biphenyl-, and cyanopropyl-substi tuted stationary phases for pressures up to 680 atm and temperatures u p to 240-degrees-C. The solute elution range varied tremendously with column choice, with the least retentive stationary phases providing th e highest elution range. However, the best resolution and largest anal ysis range were obtained with the most retentive stationary phase and the highest pressures. Increasing the temperatures above 160-degrees-C did not cause a large increase in elution pressure for the solutes us ed in this study. Exceptionally large shifts in selectivity with tempe ratures up to about 160-degrees-C occurred for the biphenyl and cyanop ropyl stationary phases. The availability of pressures higher than 680 atm, coupled with adequately retentive stationary phases used at opti mal temperatures, would further increase the analysis scope of open-tu bular supercritical fluid chromatography.