Chemistry Reference
In-Depth Information
that are safer for the environment. Significant environmentally friendly method innovations have been
developed in the field of environmental analysis for determining trace elements and organic contaminants
in soil [8, 9, 21, 58].
Instrumental methods that can manage solid samples for direct analysis, such as electrothermal atomic
absorption spectrometry (ET AAS), glow discharge-mass spectrometry (GD-MS), laser ablation-mass
spectrometry (LA-MS), electrothermal vaporization (ETV), X-ray fluorescence spectrometry (XFS), and
laser-induced breakdown spectroscopy (LIBS) are good examples of the environmentally friendly analytical
approaches for determining trace elements and major constituents in soil samples. The main advantage of these
methods is avoiding sample pre-treatments, such as chemical decomposition and dissolution. If sample pre-
treatment is mandatory for trace metal analysis, the utilization of microwave- and ultrasonic-assisted treatments
could be interesting due to the use of reduced quantities of acids and solvents coupled with energy conservation.
Most methods for sample treatment and further separation of organic compounds use organic solvents, and
this is the main source of organic waste. An ultimate goal in green chemistry is to eliminate or minimize the
use of volatile organic solvents [78]. Thus, a variety of solvent reduction, replacement and elimination has
been developed to extract and concentrate analytes [5, 9, 27, 78]. These include pressurized fluid extraction
(PFE), also known as accelerated solvent extraction (ASE) [79], ultrasound extraction (USE), microwave
assisted extraction (MAE), and supercritical fluid extraction (SFE) [9]. The main characteristic of these
techniques is the reduction of organic solvents and speed of extraction times compared to traditional liquid-
liquid extractions [8]. An example of an analytical procedure used for environmental analysis is the extraction
of pesticides from soil samples using ASE. This procedure can take minutes rather than the hours required for
Soxhlet extraction [80]. Ultrasound extraction uses high frequency acoustic waves to create microscopic
bubbles in liquids [8]. Ultrasonic irradiation may have a strong effect on several sample treatments.
Microwave-assisted extraction is an alternative method, in which digestion or extraction can be sped up by
introducing energy to heat the sample in the form of microwaves. Microwaves allow reaction times to be
significantly reduced [9]. SFE applied to solid environmental matrices containing trace pollutants has become
a routine method. The most useful supercritical fluids to green chemists are water and carbon dioxide, which
are renewable and non-flammable. SFE has been employed in a great number of soil applications covering
many organic pollutants, such as polychlorinated biphenyls [80], polycyclic aromatic hydrocarbons [81],
chlorinated benzenes (CB) and hexachlorocyclohexanes (HCH) [82].
Different analytical practices are developing rapidly. In this context, new measuring techniques and
methods have been widely used for the identification and determination of major constituents, trace elements
and organic contaminants in soil samples. The evolution of new methods for soil sample analysis include
solid-phase extraction (SPE), molecularly imprinted polymers (MIP), cloud-point extraction (CPE), ion
chromatography-inductively coupled plasma-sector field mass spectrometry (IC-ICP-SFMS), thermal
extraction cone penetrometry and immunoassays (IA), that is, enzyme-linked immunosorbent assay (ELISA).
Table 22.4 presents some relevant green analytical methods for determining major constituents, trace
elements and organic contaminants in soil samples.
22.4.2 Sediments
Sediment is any particulate matter that can be transported by fluid and that eventually is deposited as a layer
of solid particles on the bed or bottom of a body of water or other liquid.
Sample pretreatment is the most critical stage of the analytical process, mainly when solid matrices are
analyzed. Although there are references in the literature for several fast separation and detection methods,
many of these involve time-consuming sample pre-treatment, commonly, extraction procedures. The
extraction step has been the critical part in developing approaches for solid and semi-solid samples. The more
usual, simple and classic extraction procedures are based on solvents and/or diluted acids assisted by
