4 Organic compounds in soils, sediments & sludges
extraction techniques [41, 42]. However, only 36 to 72% of phenoxyacetic acid herbicides acid were recovered by this technique from clay, loam and sand. A further
limitation of the accelerated solvent extraction technique, which is shared by several
of the other newer extraction techniques reviewed here, is that selective extraction
of organics based on their polarities is difficult. For example, the case of the extraction of soil with a high organic content (9.6%) at 100
◦ C with methanol or acetone
as such or acidified with phosphoric acid with each of the extractants, large amounts
of wax-like subtances – presumably cellulose, lignin and waxes from plant cells –
were coextracted with the herbicides considered. The presence of these high molecular weight compounds in soil extracts caused interference in the final analytical finish
employed to determine the herbicides and can only be avoided in some, not all, cases
by tedious and time-consuming clean-up procedures. To a lesser extent these species
are also present in soils with a lower organic content. Subcritical water extraction
overcomes this difficulty and will be discussed further below [43].
The range of materials for which the technique is proposed includes semi-volatile
compounds, including polycyclic aromatic hydrocarbons, organochlorine pesticides,
organophosphorus pesticides, chlorinated herbicides and polychlorinated byphenyls.
Siam et al [44] investigated the interdependence of selected operating parameters
on the recovery of 16 polycyclic aromatic hydrocarbons from nine highly contaminated
soils, including a range of pressure from 1000–2400 psi, operating temperature from
40–200
◦ C, and extraction times from 2 to 16 minutes.
At the 95% confidence internal, no significance in terms of the three operating
parameters was found when considering the total polycyclic aromatic hydrocarbon
recovery. However, recoveries of some individual polycyclic aromatic hydrocarbons
were found to be dependent on operating variables. In particular, low operating
temperature of 40
◦ C were very significant for naphthalene, chrysene and benzo (b)
fluoranthene.
Wennrich et al [45] have described a method for the determination of nine
chlorophenols in soil using accelerated solvent extraction with water as the solvent
combined with solid-phase microextraction and gas chromatography-mass spectrometry. An extraction temperature of 125
◦ C and ten minute extractions were
optimal.
Hofler et al [46] also studied the application of accelerated solvent extraction with
an organic solvent, followed by clean-up and preconcentration procedures.
Hubert et al [47] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic
extraction and, in some cases, supercritical fluid extraction is an exceptionally effective
extraction technique. Hubert et al [47] studied the effect of operating variables such as
choice of solvent and temperature on the solvent extraction of a range of accelerated
persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX,
polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures of
between 20 and 180
◦ C were studied. The optimum extraction conditions use two
extraction steps at 80 and 140
◦ C with static cycles (extraction time 35 minutes) using
toluene as a solvent and at a pressure of 15 MPa.
Pyle and Marcus et al [48] achieved low ppb detection for the determination of
organochlorine insecticides in soil using accelerated solvent extraction followed by
gas chromatography ion tandem mass spectrometry. Richter et al [36] showed that
extraction techniques [41, 42]. However, only 36 to 72% of phenoxyacetic acid herbicides acid were recovered by this technique from clay, loam and sand. A further
limitation of the accelerated solvent extraction technique, which is shared by several
of the other newer extraction techniques reviewed here, is that selective extraction
of organics based on their polarities is difficult. For example, the case of the extraction of soil with a high organic content (9.6%) at 100
◦ C with methanol or acetone
as such or acidified with phosphoric acid with each of the extractants, large amounts
of wax-like subtances – presumably cellulose, lignin and waxes from plant cells –
were coextracted with the herbicides considered. The presence of these high molecular weight compounds in soil extracts caused interference in the final analytical finish
employed to determine the herbicides and can only be avoided in some, not all, cases
by tedious and time-consuming clean-up procedures. To a lesser extent these species
are also present in soils with a lower organic content. Subcritical water extraction
overcomes this difficulty and will be discussed further below [43].
The range of materials for which the technique is proposed includes semi-volatile
compounds, including polycyclic aromatic hydrocarbons, organochlorine pesticides,
organophosphorus pesticides, chlorinated herbicides and polychlorinated byphenyls.
Siam et al [44] investigated the interdependence of selected operating parameters
on the recovery of 16 polycyclic aromatic hydrocarbons from nine highly contaminated
soils, including a range of pressure from 1000–2400 psi, operating temperature from
40–200
◦ C, and extraction times from 2 to 16 minutes.
At the 95% confidence internal, no significance in terms of the three operating
parameters was found when considering the total polycyclic aromatic hydrocarbon
recovery. However, recoveries of some individual polycyclic aromatic hydrocarbons
were found to be dependent on operating variables. In particular, low operating
temperature of 40
◦ C were very significant for naphthalene, chrysene and benzo (b)
fluoranthene.
Wennrich et al [45] have described a method for the determination of nine
chlorophenols in soil using accelerated solvent extraction with water as the solvent
combined with solid-phase microextraction and gas chromatography-mass spectrometry. An extraction temperature of 125
◦ C and ten minute extractions were
optimal.
Hofler et al [46] also studied the application of accelerated solvent extraction with
an organic solvent, followed by clean-up and preconcentration procedures.
Hubert et al [47] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic
extraction and, in some cases, supercritical fluid extraction is an exceptionally effective
extraction technique. Hubert et al [47] studied the effect of operating variables such as
choice of solvent and temperature on the solvent extraction of a range of accelerated
persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX,
polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures of
between 20 and 180
◦ C were studied. The optimum extraction conditions use two
extraction steps at 80 and 140
◦ C with static cycles (extraction time 35 minutes) using
toluene as a solvent and at a pressure of 15 MPa.
Pyle and Marcus et al [48] achieved low ppb detection for the determination of
organochlorine insecticides in soil using accelerated solvent extraction followed by
gas chromatography ion tandem mass spectrometry. Richter et al [36] showed that