Chemistry Reference
In-Depth Information
Figure 3.
IR detector signal and TREF oven temperature collected during a full cross-fractionation run.
chromatogram of one of the TREF frac-
tions; therefore the MWD of each narrow-
CCD fraction is obtained.
The dissolution and injection processes
are illustrated in Figure 4, with an expanded
view of the temperature and IR absorbance
recorder signals plot. The dashed horizon-
tal arrow indicates the dissolution time of
the polymer fraction within the TREF
column. The solid downwards arrow shows
the injection. Solvent flows through the
TREF column for a time long enough to
elute all the species dissolved at that
temperature. The injection valve is closed
as indicated by the solid upwards arrow.
At that time, the TREF oven tempera-
ture is increased to that of the next
fractionation step. Meanwhile, the TREF
polymer fraction travels through the GPC
columns, being fractionated by molar mass,
producing the peak in the IR detector signal
indicated by the circle in Figure 4.
An interesting improvement has been
implemented in this system to allow for the
injection of one fraction before the pre-
vious one has completely exited the GPC
columns, hence reducing the overall ana-
lysis time. In Figure 5, a direct comparison
of standard and overlapped injection ana-
lyses is provided. In a period of three hours,
Figure 4.
Detailed view of the injection process.
