Chemistry Reference
In-Depth Information
22.5.2 Particulates
Particles are of great interest in atmospheric analysis because of their impact on human health. Most particle
analyses fall into two categories: mass determination and chemical composition [130, 133].
Particles are collected based on filtration, gravitational and centrifugal sedimentation, inertial impaction
and impingement, diffusion, interception or electrostatic or thermal precipitation. The choice of the method
depends on parameters such as composition and size of the particles.
After collection, the mass of the collected particles can be determined by gravimetric methods,
-ray
attenuation, piezoelectric microbalance and oscillating microbalance. Particle size is also of great interest.
Optical methods, atomic force microscopy, scanning tunneling microscopy, electrical mobility analyzers,
diffusion separators, aerodynamic particle size and condensation particle counters are the choices for analysis
[130]. Currently, there is no technique capable of measuring the size distribution of the atmospheric aerosols.
A combination of methods must be used for such analysis.
Chemical composition of the particles may be determined by numerous methods. The choice depends
primarily on the nature of these particles (inorganic and organic components).
Colorimetric methods were extensively used in the past to determine inorganic elements [130] but have
been replaced by other characterization techniques [130, 131]. The main reason is that these methods are
subject to interferences, particularly in the case of complex environmental samples. Although this replacement
was not based on green aspects, one of the consequences of the abandonment of colorimetric methods was to
develop greener methods of analysis for particulates. These methods fall into two categories: X-ray
fluorescence (XRF), particle-induced X-ray emission (PIXE), neutron activation (NA), X-ray photoelectron
spectroscopy (XPS); and mass spectrometry (MS), which do not require leaching of the sample prior to
analysis, making them more green procedures. Atomic absorption spectrometry (AAS), optical emission
spectrometry (OES), inductively coupled plasma spectroscopy (ICP), and anodic stripping voltammetry
(ASV) require the extraction of elements into a solution that is analyzed.
Inorganic ions present in particulates are analyzed by colorimetric methods, ion chromatography, and
selective ion electrodes. These methods require solubilization of the sample. Infrared, Raman spectroscopy
and mass spectrometry do not require previous solubilization [130].
Organic elemental carbon can be determined by thermal, optical, digestion and extraction techniques.
Digestion has not shown to present clear advantages over thermal methods, but all of the above procedures
may be subjected to serious errors. Speciation of organic compounds may be performed by thermal desorption
or solvent extraction followed by GC-MS or HPLC. Solvent extraction may require the use of toxic solvents
and inevitably generates liquid waste [130]. A green approach was to replace ordinary solvents by supercritical
fluids, such as CO
2
[131, 132]. Thus, the use of large volumes of solvent is avoided, and it is not necessary to
concentrate the extract (in this step losses of analytes may occur). Supercritical fluids can be used at lower
temperatures, thus minimizing thermal decomposition and/or formation of artifacts that may take place using
thermal desorption techniques [131, 132]. The new green techniques have potential applications in atmospheric
analysis [133].
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References
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Practical Environmental Analysis
, The Royal Society of Chemistry,
Cambridge.
2. Rocha, F.R.P.; Nóbrega, J.A. and Fatibello-Filho, O. (2001) Flow analysis strategies to greener Analytical Chemistry.
An overview,
Green Chem
.,
3
, 216-220.
3. de la Guardia, M. and Ruzicka, J. (1995) Guest editorial. Towards environmentally conscientious Analytical
Chemistry through miniaturization, containment and reagent replacement,
Analyst
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