Chemistry Reference
In-Depth Information
mechanical shaking, Soxhlet distillation, ultrasonic baths or probe devices. These procedures use large
solvent volumes, are tedious, and the extracts must be handled before analyzing them, which can result in a
low percent recovery for the analyte being assessed [11, 14]. Using harmful chemicals and large volumes of
solvents cause environmental pollution, health hazards to laboratory personnel and extra operational costs for
waste treatment. Ideally, sample preparation techniques should be fast, easy to use, inexpensive and compatible
with a range of analytical instruments; therefore, the current trend is towards simplification and miniaturization
of the sample preparation steps and decreasing the quantities of organic solvents used [18]. Some green
solvent extraction techniques for the analysis of solid matrices have been developed to shorten the analytical
procedures and minimize waste solvents, requiring much smaller volumes of solvents; in some techniques,
no solvent or virtually no solvent is used, which are called solventless [7] (see Section 2.2.2).
Table 22.5 presents some relevant environmental analytical methods applied for sediment samples, which
present the green characteristics mentioned above.
22.4.3 Wastes
Waste management must be faced under the principles of minimization, recovery, reuse and recycling. Taking
into account that one of the main aspects of the Green Analytical Chemistry is to avoid waste generation, the
best way to overcome this target is relatively simple in principle: the best waste is the one that is not generated.
Therefore, in-field direct sample analysis is the ideal choice because no reagents are used [126]. However, it
is usually impossible to avoid waste generation in industrial, teaching and analytical procedures. Many of
these are official and certified methods adopted by environmental organisms [127]. Due to this aspect, a new
green alternative must be developed, validated and certified.
Similar to analyses of sediments and soils, solid waste analysis can become greener if some strategies are
adopted [126, 127]:
(1)
miniaturization and automation of analytical methods;
(2)
development of less-consuming energy and reagent methods;
(3)
the use of less toxic (or even non-toxic) solvents and reagents; and
(4)
on-line decontamination of wastes.
Strategies (1) through (3) are applicable for teaching laboratories. This is of utmost importance because
students will be given an opportunity to discover Green (Analytical) Chemistry long before reaching their
first job. Also, an important difference between industrial and laboratory waste is the amount generated in
each case: the former is generated in much higher amounts.
Waste characterization demands many analytical tools. Supercritical fluid extraction, solid-phase extraction,
microwave- and ultrasound-assisted extraction, pressurized fuel extraction, CG-MS, HPLC-MS, and MS-MS
are currently in use for the analysis of biodegradable and non-degradable wastes [127-129]. Heavy metals,
phenols, chlorophenols, linear alkylbenzene sulfonates, antibiotics, aromatic hydrocarbons and fluorinated
compounds have been successfully analyzed by these techniques with minimum waste generation. Solid
waste analysis follows the same tendencies for sediment and soil analyses, but it appears that solid waste
management remains an interesting field to develop green analytical procedures because there are apparently
few green procedures currently in use.
However, what should be done when dealing with waste? The availability of areas for landfills are
limited and subjected to increasing environmental restraints. The options are numerous, and the choice
depends on the nature of the waste. Thermal degradation is a classic final destination for organic compounds.
Incineration and co-processing are common alternatives, but the latter is better from an environmental
viewpoint. It accepts a wide variety of waste for energy recovery during clinker manufacturing. Also,
