selection of the solvent; however, extraction efficacy is significantly influenced also
by other parameters, such as pressure, temperature, particle size, agitation, etc.
Working under conditions of elevated pressure facilitates the solvent to penetrate
sample pores. An increase in temperature usually increases solubility of the
extractables in the solvent, diffusion coefficients and solvent’s capacity to disrupt
matrix-solute interactions (Barahona et al. 2019). However, in certain cases the
solvent selectivity towards desired extractable is higher at lower temperatures. The
extraction rate is enhanced with solid particle size reduction. In this context, samples
are crushed, ground, milled, flaked or sliced into thin strips prior to extraction (Berk
2013). This gives an increased surface area per unit volume of solids to be leached
and reduced distance to be traversed within the solid by the solvent and the extract
(Tiwari 1995). The higher extraction yields can be often obtained by agitation which
increases the contact surface between the sorbent and the analyte (Tashakkori et al.
2017). It does not affect extraction rate in case that any variations in extraction yields
can be attributed to the other factors (e.g. heat treatment history) rather than to
kinetic ones (Cogan et al. 1967).
The general solid-liquid extraction procedure is applicable in a range of fields
including environmental monitoring. It can be used to extract a broad range of semivolatile environmental pollutants that partition primarily on soils and sludges, such
as polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs)
and pesticides; it is probably the most widely used procedure in the analysis of
pesticides in solid samples (Barahona et al. 2019). Because of the potential health
effects, identification and quantification of these species is of academic interest and
also widely practiced in the environmental consulting industry and in government
agencies (JoVE 2019).
Solid-liquid extraction includes various techniques based on the contact of a
certain amount of sample with an appropriate solvent (Barahona et al. 2019).
Shaking is a very simple way to extract pollutants bound weakly to the sample;
for strongly bound analytes it might not be effective enough. The method is
applicable to a wide range of soil types and petroleum contaminants (Schwab
et al. 1999). The principle of this method is based on the manual or automatic
shaking of the sample in the presence of solvent for a certain period of time. The
preferable organic water-miscible solvents are acetone, acetonitrile and methanol.
Water-immiscible solvents (e.g. dichloromethane, hexane) can also be used,
depending on the properties of the analyte. In order to make this process more
efficient, shaking can be coupled to UAE. The acoustic cavitation and some
mechanical effects induced by ultrasound enhance the agitation of the solvent and
solute, thus increasing the contact area between solid and liquid phase, resulting in a
better penetration of solvent into sample matrix. Owing to this, extraction times and
the amount of solvents used in the shaking process are considerably reduced (Gutte
et al. 2015; Barahona et al. 2019).
Although first described in 1879, Soxhlet extraction is still one of the most
relevant and frequently used solid-liquid extraction techniques in environmental
analysis. It has been used for an isolation of non-polar and semi-polar trace organic
contaminants from a wide variety of solid materials, such as sediments, soils,
5 The Recent Strategies Employed in Chemical Analysis of Contaminated Waters,. . .
143
by other parameters, such as pressure, temperature, particle size, agitation, etc.
Working under conditions of elevated pressure facilitates the solvent to penetrate
sample pores. An increase in temperature usually increases solubility of the
extractables in the solvent, diffusion coefficients and solvent’s capacity to disrupt
matrix-solute interactions (Barahona et al. 2019). However, in certain cases the
solvent selectivity towards desired extractable is higher at lower temperatures. The
extraction rate is enhanced with solid particle size reduction. In this context, samples
are crushed, ground, milled, flaked or sliced into thin strips prior to extraction (Berk
2013). This gives an increased surface area per unit volume of solids to be leached
and reduced distance to be traversed within the solid by the solvent and the extract
(Tiwari 1995). The higher extraction yields can be often obtained by agitation which
increases the contact surface between the sorbent and the analyte (Tashakkori et al.
2017). It does not affect extraction rate in case that any variations in extraction yields
can be attributed to the other factors (e.g. heat treatment history) rather than to
kinetic ones (Cogan et al. 1967).
The general solid-liquid extraction procedure is applicable in a range of fields
including environmental monitoring. It can be used to extract a broad range of semivolatile environmental pollutants that partition primarily on soils and sludges, such
as polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs)
and pesticides; it is probably the most widely used procedure in the analysis of
pesticides in solid samples (Barahona et al. 2019). Because of the potential health
effects, identification and quantification of these species is of academic interest and
also widely practiced in the environmental consulting industry and in government
agencies (JoVE 2019).
Solid-liquid extraction includes various techniques based on the contact of a
certain amount of sample with an appropriate solvent (Barahona et al. 2019).
Shaking is a very simple way to extract pollutants bound weakly to the sample;
for strongly bound analytes it might not be effective enough. The method is
applicable to a wide range of soil types and petroleum contaminants (Schwab
et al. 1999). The principle of this method is based on the manual or automatic
shaking of the sample in the presence of solvent for a certain period of time. The
preferable organic water-miscible solvents are acetone, acetonitrile and methanol.
Water-immiscible solvents (e.g. dichloromethane, hexane) can also be used,
depending on the properties of the analyte. In order to make this process more
efficient, shaking can be coupled to UAE. The acoustic cavitation and some
mechanical effects induced by ultrasound enhance the agitation of the solvent and
solute, thus increasing the contact area between solid and liquid phase, resulting in a
better penetration of solvent into sample matrix. Owing to this, extraction times and
the amount of solvents used in the shaking process are considerably reduced (Gutte
et al. 2015; Barahona et al. 2019).
Although first described in 1879, Soxhlet extraction is still one of the most
relevant and frequently used solid-liquid extraction techniques in environmental
analysis. It has been used for an isolation of non-polar and semi-polar trace organic
contaminants from a wide variety of solid materials, such as sediments, soils,
5 The Recent Strategies Employed in Chemical Analysis of Contaminated Waters,. . .
143