TRI-N-BUTYLPHOSPHATE/CO2 AND ACETONE/CO2 PHASE BEHAVIORS AND UTILITIES IN CAPILLARY SUPERCRITICAL-FLUID CHROMATOGRAPHY

Because the phase behavior of the mobile phase must be known before conclusions fr-om supercritical-fluid chromatography (SFC) can be considered reliable, the phase behaviors of tri-n-butylphosphate/CO2 and acetone/CO2 were thoroughly determined in a variable-volume view cell at conditions applicable to SFC (0-20 mol % modifier, 25-140 degrees C, and 80-415 atm). The chromatographic utilities of the binary fluids were determined with test compounds (condensed tannins and steroids). Although the UV-absorbance detector base-line rise was severe with acetone/CO2, chromatographic performance was not compromised. Standard base-line correction methods were used to produce conventional-looking chromatograms. The chromatographic performance with tri-n-butylphosphate/CO2 was unsatisfactory (erratic retention). Static restrictors (integral, frit, crimped Pt/Ir, linear, and valves) produced erratic flow. Heating the restrictors to 250-400 degrees C did not improve performance. Reasons for the compromise in chromatographic performance are proposed.