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251
c)
The software performs a regression analysis to extrapolate to
θ
= 0
(sin
2
(
θ
/2) = 0) and finds Kc
i
/R
θ
=0
, which obeys the simple equation:
Kc
R
θ
=
0
=
1
M
w
+
2
A
2
c
+
...
⎛
⎝⎜
⎞
⎠⎟
We need to know A
2
(from separate experiments or literature) in order to allow
further calculations.
This is generally the case for SEC-MALLS
. In practise,
we often operate at such low concentrations (typically 1 – 10
µ
g/ml). Thus,
2A
2
c
i
<< 1/M
w
and the 2A
2
c term can in practise be neglected
46
. Thus, M
w,I
is
found.
The process is then repeated for all 1000-5000 slices.
d)
The software also calculates the slope of the fitted line, which gives the
radius of gyration (R
G,i
), at each slice since (generally):
46
This may not be true in cases where a large amount of material is injected (typically for low
molecular weights). The influence of A
2
can easily be checked by changing the value in the
software and observe to which extent it changes the molecular weight.