Environmental Engineering Reference
In-Depth Information
The retention ratio ( R ) in FFF is defi ned by:
t
t r
0
R
(6.6)
=
where t 0 is the void time and t r is the retention time. For highly retained components,
R can be approximated by:
R ≈ 6λ
(6.7)
while R can be estimated as follows for intermediate retention:
(
)
(6.8)
1 2
"
R =
6
λ
coth
2
λ
λ
The fundamental retention parameter (
) is defi ned as the mean distance of the
component from the wall ( l ) divided by the channel thickness ( w ):
λ
l
w
D
Uw
(6.9)
λ ==
where D is diffusion coeffi cient and U is the fi eld induced force on the particles.
Field - fl ow fractionation has been very valuable in environmental studies on
natural colloids using both optical detectors (UV/Vis, Fluorescence and SLS/DLS)
(v.d.Kammer et al. , 2005) and ICP-MS (Beckett and Hart, 1993; Hassellö v et al. ,
2007). In addition, FFF has been applied for characterizing a wide range of manu-
factured NPs including silica, titania, metals, metal oxides, carbon black and carbon
nanotubes (Schimpf et al. , 2000; Siripinyanond and Barnes, 2002; Chen and Selegue,
2002 ; Fraunhofer et al. , 2004 ; Gimbert et al. , 2007 ; Moon et al. , 2004 ). An example
of FFF-ICPMS determination of size distribution in a copper(II) oxide nanopow-
der is shown in Figure 6.8. The obtained size distribution is a mass (or particle
volume) distribution since the ICP-MS is analysing the mass concentration in each
size fraction.
Hydrodynamic diameter (nm)
0
100
200
300
400
40000
20000
500
1000
1500
2000
FFF Retention time (s)
Figure 6.8 An example of a FFF-ICPMS fractionation of engineered nanoparticles (CuO
nanopowder), where the lower x axis is the raw data (retention time) and the upper is the
converted size distribution. The y axis shows the copper signal from ICP-MS.
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