Chemistry Reference
In-Depth Information
It remains now to translate this polystyrene calibration curve to one that will be
effective in the same apparatus and solvent for other linear polymers. (Branched
polymers and copolymers present complications and are discussed separately
later.) This technique is called a
universal calibration
, although we shall see that
it is actually not universally applicable.
Studies of GPC separations have shown that polymers appear in the eluate in
inverse order of their hydrodynamic volumes in the particular solvent. This forms
the basis of a universal calibration method since
Eq. (3-64)
is equivalent to
ln
ð½η
M
Þ 5
ln
ð
2
:
5
L
Þ 1
ln lim
c-
0
V
(3-94)
]
M
is a direct function of the hydrodynamic volume of the sol-
ute at infinite dilution. Two different polymers that appear at the same elution
volume in a given solvent and particular GPC column set therefore have the same
hydrodynamic volumes and the same [
The product [
η
]
M
characteristics.
The conversion of a calibration curve for one polymer (say, polystyrene, as in
Fig. 3.11
) to that for another polymer can be accomplished directly if the
Mark
η
Sakurada equations are known for both species in the GPC sol-
vent. From
Eq. (3-70)
, one can write
Houwink
K
i
M
a
i
1
1
½η
i
M
i
5
(3-95)
i
10
7
10
6
10
5
10
4
10
3
130
140
Elution volume (mL)
150
160
FIGURE 3.11
Polystyrene calibration curve for GPC, where M is the molecular weight of the anionic
polystyrene standard samples.
