Analysis and Characterization of Manufactured Nanoparticles in Aquatic Environments - Environmental and Human Health Impacts of Nanotechnology - page 220

6.2.2 Sampling, NP Extraction, Sample Preparations

Environmental colloidal systems are dynamic and consist of continuous particle
formation and dissolution, removal and adsorption of organic matter and microbial
degradation (Chen and Buffl e, 1996b). It is well known that natural NPs in the
colloidal state are easily disturbed in water, groundwater, soil and sediment during
sampling, handling and storage (Backhus et al. , 1993 ; Puls, 1990 ; Citeau et al. , 2006 ).
Changes can include agglomeration, microbial growth, degradation or adhesion to
containers. It is, therefore, desirable to use in situ techniques that remove the sam-
pling step (Ledin et al. , 1994; Kim and Walther, 2007; Maldiney and Mouchel, 1995),
but there are almost none available that can provide more than very basic
information. Instead, efforts have been put into sampling of the colloids as gently
as possible, minimizing handling and storage to avoid perturbations (Chen and
Buffl e, 1996a; Lead et al. , 1997; Chanudet and Filella, 2006). These procedures opti-
mized for natural NPs should be suitable also for manufactured NPs in the same
matrices.
Most of the analytical techniques being discussed in this chapter are applicable
to dispersed NPs. Although free NPs and suspended aggregates are the most impor-
tant fractions in many applications, deposited or adhered NPs are also important
in some matrices (e.g. soil and sediments). Therefore, it is important to consider
methods to extract or detach NPs from solid matrices, as well as methods to char-
acterize the attached NPs. Such detachment methods can include addition of dis-
persion agents (e.g. sodium pyrophosphate) and sonication prior to analysis. The
same considerations also apply to the interaction of manufactured NPs as they do
with the interactions of natural NPs, whether the manufactured NPs should be
extracted/detached from natural materials or analysed as present. Sonication is
often used to deliver energy to an agglomerated system to break apart reversibly
agglomerated particles. It does not provide stabilization, but only the de-
agglomeration energy. Similarly, dispersion agents alone are usually not suffi cient
to de-agglomerate and stabilize agglomerated NPs. A drawback of sonication as a
dispersion tool is that sonication increases drastically the collision rate between
NPs and can thus lead to an induced agglomeration instead, depending on the
particles, media and sonication conditions. Fullerenes can be chemically extracted
with solvents (Fortner et al. , 2005; Nowack and Bucheli, 2007). In hazard assessment
of nanopowders it is important to take into account the representative sampling of
the powders (Powers et al. , 2007 ).

6.2.3 Light Scattering Methods

A coherent electromagnetic wave of laser light will interact with matter and induce
an oscillating electric dipole in a particle. These induced dipoles will in turn
re-radiate light. This is the basic principle of light scattering. Light scattering
phenomena can be used in several different characterization techniques to deter-
mine different size related properties and also concentration. In addition to light
scattering, interaction of light with the particles can also lead to absorption,
fl uorescence, refraction and diffraction, which are partly covered in the spectros-
copy section.