MOBILE FLUID INTERACTION WITH THE STATIONARY PHASE IN SUPERCRITICAL FLUID CHROMATOGRAPHY

The mass spectrometric tracer pulse chromatography (MSTPC) method is used to study the effect of methanol as a mobile fluid additive on the partition behavior of n-pentane into 5% phenylmethylsilicone stationary phase under conditions of capillary supercritical fluid chromatography (SFC). The partition isotherms of n-pentane are measured in the presence of 0, 0.5, 1.0, and 5.0% methanol in supercritical n-pentane at 220°, 260°, and 300°C and pressures between 500 and 850 psi. The addition of methanol does not cause significant change in the partition behavior of the n-pentane fluid into the stationary phase. The data obtained show that mobile fluid uptake by the stationary phase decreases with increasing temperature and pressure, indicating that the stationary phase swelling phenomenon in SFC could be largely due to stationary phase thermal expansion or relaxation.