The
fundamental principles of SFC are essentially the same as those for other modes
of column chromatography. There are, however, significant differences that
require different approaches to experimental work and to data analysis and
interpretation. These differences are due primarily to the compressibility of
the fluid and to the effect of pressure and pressure drop on the retention
factor and plate height. The fluid density, temperature, velocity, and
viscosity all vary as the fluid expands along the column.Modern supercritical
fluid chromatography (SFC) is a high resolution chemical separation technique,
closely related to high performance liquid chromatography (HPLC) and, in fact,
uses most of the same instrumentation, columns, and software. The primary
difference between the two techniques is the replacement of most of the liquid mobile
phase used in HPLC with highly compressed, dense carbon dioxide  CO2 along
with relatively small additions of a polar modifier, such as an alcohol The fundamental
principles of SFC are essentially the same as those for other modes of column
chromatography. The differences are due primarily to the compressibility of the
fluid and to the effect of pressure and pressure drop on the retention factor
and plate height. The fluid density, temperature, velocity, and viscosity all
vary as the fluid expands along the column. The local retention factor is a
function of local temperature and density, and the local plate height can be
written in terms of the mass flow rate, temperature, and density. The kinetic
performance of SFC is superior to that of HPLC when columns are operated near
the optimum velocity.(Berger and Deye,1991). The kinetic performance of SFC is
superior to that of HPLC when columns are operated near the optimum velocity,
but as in HPLC the overall kinetic performance is limited by the maximum
operating pressure and flow rates provided by available instrumentation. There
are, however, significant differences that require different approaches to
experimental work and to data analysis and interpretation. These differences
are due primarily to the compressibility of the fluid and to the effect of
pressure and pressure drop on the retention factor and plate height. The fluid density,
temperature, velocity, and viscosity all vary as the fluid expands along the
column. The local retention factor is a function of local temperature and
density, and the local plate height can be written in terms of the mass flow
rate, temperature, and density. The apparent values of the retention factor and
plate height at the column outlet can then be expressed as the appropriate
temporal and/or spatial averages of the local value