Chemistry Reference
In-Depth Information
Elution vol. (cm
3
)
Molecular weight of the polystyrene standards
Mol. Wt. of PP
10,000
160
2,500
50,000
145
12,000
100,000
132
23,000
500,000
120
105,000
14.0
13.0
12.0
PS
11.0
10.0
9.0
PP
8.0
7.0
110
120
130
140
150
160
170
Elution volume (cm
3
)
The molecular weight of the fraction of the unknown PP sample showing an elution vol-
ume of 150 cm
3
is
6000.
B
Note that the universal calibration relations apply to polymeric solutes in very
dilute solutions. The component species of whole polymers do indeed elute effec-
tively at zero concentration but sharp distribution fractions will be diluted much
less as they move through the GPC columns. Hydrodynamic volumes of solvated
polymers are inversely related to concentration and thus elution volumes may
depend on the concentration as well as on the molecular weights of the calibration
samples. To avoid this problem, the calibration curve can be set up in terms of
hydrodynamic volumes rather than molecular weights. A general relation
[20]
is
4
π½η
M
V
5
(3-98)
μ1
4
π
Lc
ð½η 2 ½η
θ
Þ
Here
c
is set equal to the concentration of the solution of a sharp distribution
calibration standard used to establish the calibration curve, and [
η
]
θ
(
Eq. 3-40
)
