Chemistry Reference
In-Depth Information
the components will be according to
CRYSTAF rather than TREF elution
temperatures, as separation occurred in
the crystallization and not in the dissolution
process.
Proper analysis by this technique
demands that the temperature range of
the polymer components to be separated,
D
T
p
is within the crystallization temperature
range
where the dynamic crystallization cycle, at a
crystallization solvent flow of F
c
, is followed
by the temperature rising elution cycle,
with a solvent flow F
e
as in TREF. The new
process is known as crystallization elution
fractionation (CEF), as it combines the
separation obtained in the crystallization
step with the one obtained in the elution
cycle; this is schematically represented in
Figure 1.c by the extended separation of the
three components at the exit of the column
in CEF analysis as compared to the TREF
approach.
It is quite interesting that the separation
power of CRYSTAF (obtained by dynamic
crystallization) and TREF are combined in
CEF when both systems are based on the
same crystallizability principles, and when
TREF requires both cycles
D
T
c
, and the full power of the dynamic
crystallization analysis will be obtained when
D
T
p
is equal to the
D
T
c
used, resulting in the
components crystallizing along the whole
length of the column. When the range of
D
T
p
is narrower and within the range of
D
T
c
, only
a fraction of the separation power, equiva-
lent to the ratio of the two temperature
ranges, will be obtained.
. On the
other hand, one could expect that analysis
of particular blends where differences in
supercooling result in separation of the
components during crystallization in an
opposite direction to the one obtained by
elution-melting would result in poor CEF
separation.
per se
Crystallization Elution Fractionation
Once dynamic crystallization was devel-
oped as a new separation process, it was
easy to realize the possibility to combine
this crystallization step with a final elution
cycle as in TREF to obtain a new
extended
separation. This is represented in Figure 1.c
Figure 2.
Schematic diagram of the combined CEF, dynamic crystallization and TREF instrument.
