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242
biopolymers contain tightly bound water (even after drying), or other
impurities.
Light scattering normally requires that the samples do not absorb light at the
wavelength of the laser. Any absorption of incident and scattered light must
be corrected for if it cannot be avoided.
Also, fluorescence may impair the measurements, as fluorescence can be
much stronger than the scattering. Polymers such as lignosulfonates face this
problem. Fluorescence (emission) can be eliminated by using special optical
filters (‘narrow band pass’). The filters eliminate fluorescence at wavelengths
other than for the scattered light itself.
6.2.10.
Light
scattering
in practise.
Light scattering with modern instruments is quite straightforward. Here is a
brief description.
1.
Prepare samples with different known concentrations, e.g. 0.2 – 1.0
mg/ml (varies with M
w
and A
2
)
2.
Samples must be free of particles and aggregates (filtration or
ultracentrifugation)
3.
(dn/dc) and n
0
must be known (tabulated or measured separately)
⇒
K
4.
Measure i
θ
at different angles for all concentrations, calculate the
Rayleigh factor (R
θ
), and obtain a matrix of raw data. :
Conc.
c
1
c
2
c
j
Angle
θ
1
i
1,1
→
Kc
1
/R
1,1
i
1,2
→
Kc
2
/R
1,2
i
1,j
→
Kc
j
/R
1,j
θ
2
i
2,1
→
Kc
1
/R
2,1
i
2,2
→
Kc
2
/R
2,2
i
2,j
→
Kc
j
/R
2,j
θ
i
i
i,1
→
Kc
1
/R
i,1
i
i,2
→
Kc
2
/R
i,2
i
i,j
→
Kc
j
/R
i,j
c
1
c
2
c
3
c
4
c
0
= 0
(blank)