Self-Assembly of Synthetic and Biological Polymeric Systems of ...

microscope, there are two polarized filters, the polarizer and the analyzer. The polarizer is
situated below the specimen stage, and the analyzer is situated above the objectives and can
be moved in and out of the light path as required. When both the analyzer and polarizer are in
the optical path, in a crossed configuration, no light passes through the system and a dark field
of view is present in the eyepieces.
Figure 2.29. Polarized light optical microscope configuration.
2.11.3.- Emission spectroscopy
Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is a widespread technique
for elemental analysis of a sample (56). In Figure 2.30, a scheme of an ICP-AES instrument is
shown. A plasma source is used to make specific elements to emit light, after which a
spectrometer separates this light in their characteristic wavelengths. This technique is
especially suited for direct analysis of liquid samples. The sample solution is transformed into
an aerosol by a nebuliser. Small droplets (1-10 μm) are transferred by an argon plasma. When
the aerosol droplets enter the hot area of plasma, they are converted into salt particles. These
salt particles are split into individual molecules that will subsequently fall apart to atoms and
ions. In the plasma, even more energy is transferred to the atoms and ions, promoting the
excitation of their electrons. When these excited atoms and ions back to a lower excitation
state or to their ground state they will emit electromagnetic radiation in the ultra-violet/visible
range of the spectrum. The classical approach for ICP-AES measurement is to collect and
measure the emitted radiation radially, i.e. the optical axis is orthogonal to the central channel
of the ICP. The limit of detection is in de order of ca. ng/ml.
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