Environmental Engineering Reference
In-Depth Information
10.3 Dry Samples
Samples like dry or fresh leaves (among them also spices, tea, etc.), flour, lyoph-
ilized food (powder), potato chips, etc., are particularly easy to observe. They can
just be put on the adhesive Carbon disc of the stub and studied as such or, when they
are relatively large and their surface is irregular, they can be cut. In that case, both
sides of the sections must be examined. If incidental or engineered nanosized
particles are on the samples or embedded in it, they can be spotted by difference
of atomic density with the surrounding matrix. The morphology of fresh samples
(for instance, a leaf) must be observed at low energy, down to 5 keV (Fig.
10.1
). On
the
y
-axis of the EDS spectra there is the intensity of the signal in counts while on
the
x
-axis is the energy in keV.
Some problems can be met with some industrial snack foods because of
their very high content of Sodium chloride, a compound that dwarfs all the particles
that may be present. So, much patience is required by the operator to tell kitchen
salt from other particles. Some relevant results are presented in Figs.
10.2
and
10.3
.
Another difficulty is the analysis of rubbery matrices like chewing gum. If the
analysis is carried out using a high-energy beam (at 30 keV), the sample is spoilt
and the results nullified. It is therefore necessary to work at lower voltage, for
instance 10-15 kV. But such a low energy is not enough to get the elemental
spectrum because of the underestimation of the elements with the peaks at high
energy. With the combination of the two modes, information on both morpholog-
ical and chemical nature of the particles can be obtained.
a
b
c
Ti
C
Mn
Si
O
C
Fe
O
Si
P
AI
K
AI
Ca
Ca
Mg
K
Fe
0.80 1.60 2.40 3.20 4.00 4.80
5.60
6.40 7.20
1.00 2.00 3.00 4.00 5.00 6.00
7.00 8.00 9.00
Fig. 10.1 The SEM image shows the skin of a peach with small debris coming from environ-
mental pollution. The debris are metallic alloys composed of: (b) Titanium, Silicon, Aluminum,
Calcium, Magnesium, Potassium, Iron; and (c) Manganese, Silicon, Iron, Phosphorus, Aluminum,
Potassium, Calcium. Potassium and Calcium are elements belonging to the skin, while the other
elements belong to industrial environmental pollution deposited on the peach
s skin
'
