Supercritical fluid chromatography is a powerful technique for
analysis, and it also provides a useful tool for
the measurement of thermodynamic properties. For any application,
the method involves equilibration between
the mobile supercritical fluid phase and the polymeric stationary
phase. The mobile-phase properties are
often modified substantially with the addition of polar or protic
cosolvents, but these adducts also cause
changes in the stationary phases. In situ FTIR spectroscopy and
the swelling of poly(dimethylsiloxane) (PDMS)
are combined to quantify these changes due to partitioning of the
cosolvent into and the swelling of the
polymeric stationary phase as a function of fluid pressure. These
results are used to evaluate the magnitude
of the corrections for the changes in retention time of analytes, which
affects both analytical methods and
thermophysical property measurement.