Analysis and Characterization of Manufactured Nanoparticles in Aquatic Environments - Environmental and Human Health Impacts of Nanotechnology - page 231

In addition to size characterization, shape information has also been demon-
strated for FFF in combination with microscopy or light scattering methods (Beckett
et al. , 1997; v.d.Kammer, 2005; Baalousha and Lead, 2007).
The main advantages of FFF are the relatively mild fractionation, wide operating
size range (1-800 nm for Flow FFF and 30-800 nm for Sedimentation FFF) and
versatility in terms of the detector possibilities both on-line and off-line (Hassellö v
and v.d.Kammer, 2005). The main limitation of FFF is that the versatility comes
with a rather high complexity. The key to successful FFF analysis is proper optimi-
zation of the carrier composition for a new sample in order to minimize particle-
particle and particle-wall interactions, while still allowing particles to approach the
accumulation wall almost infi nitely close.

6.2.5.5 Size Exclusion Chromatography

Size exclusion chromatography (SEC) is a size fractionation method where parti-
cles are separated through a column with a porous packing material that has a
distribution of pores in the size range of particles to be fractionated (Barth and
Boyes, 1992). The particles are separated based on to their hydrodynamic volume
(size and shape) according to their ability to enter the porous structure of the
packing materials. Larger particles enter pores to a lesser extent than smaller par-
ticles. Each SEC column has a certain operating size (or molar mass) window
depending on its pore size distribution. The fi rst eluting, oversized particles are
those outside the operating window, then comes the fractionated particles and
fi nally the ' salt peak ' containing ions and molecules that have passed through the
complete pore volume. SEC has been applied to carbon nanotubes and fullerenes
and, as described in a later section, to natural organic and inorganic nanomaterials
(Duesberg et al. , 1998 ; Perminova et al. , 2003 ; Vogl and Heumann, 1997 ; Jackson
et al. , 2005 ).

6.2.5.6 Hydrodynamic Chromatography

Hydrodynamic chromatography (HDC) is a size fractionation method where the
separation takes place in narrow open capillaries, or in wider capillaries with non-
porous packing materials that form capillary paths. Due to physical size restrictions,
the centre of mass of a particle cannot come infi nitely close to the walls, while a
smaller particle can approach the wall closer than a larger one. Since the fl ow veloc-
ity is higher away from the wall, the elution order is the same as in SEC (larger
particles fi rst then small). The separation effi ciency of HDC is very poor, but the
operating size range is very good ( 5 -300 nm). HDC has been successfully applied

for the fractionation of NPs (Williams et al. , 2002 ; Tiede, 2008 ).

∼

6.2.5.7 Electrophoresis and Capillary Electrophoresis

Electrophoresis is a group of fractionation methods using the fact that charged
particles will move in an electric fi eld. The media can be a gel (Gel Electrophoresis
or Capillary Gel Electrophoresis) or an electrolyte. The particles travel at a velocity
(v), which is proportional to the applied electric fi eld (E), and the coeffi cient is