8 Organic compounds in soils, sediments & sludges
moderately polar pesticides including triazines [116–117] sulphonyl areas [110–112],
organochlorine insecticides [111, 116], flumetron [110] and other herbicides [123].
An example of the application of supercritical carbon dioxide [114] and subcritical (hot) water extraction is the determination of the widely used pre-emergent
herbicide dacthal and its mono and diacid metabolites in soil. These compounds were
sequentially extracted from soils by first performing a supercritical hot water extract
for 15 minutes at 150
◦ C and 500 bar to recover dacthal, followed by a subcritical hot
water extraction to recover the metabolites, which were then trapped in-situ on a strong
anion exchange disc placed over the exit frit of the extraction cell. Dacthal was combined with the metabolites by placing the disc into a gas chromatograph autosampler
vial containing the supercritical fluid extract. The metabolites are then simultaneously
eluted from the disc and derivatised to their ethyl esters by reaction with ethyl iodide
at 100
◦ C. Meyer et al [120] showed that supercritical fluid extraction results can give
recoveries comparable to Soxhlet extraction methods, even for soils with high carbon contents McNally et al [103, 109] have studied factors affecting the supercritical
fluid extraction of soils. It was shown the soil type affects that recovery of moderately
polar analytes. In general the organic carbon content of the soil governs analytical
recovery.
Online coupling of supercritical fluid extraction and high-performance liquid chromatography considerably decreases sample preparation and analysis time [122, 123].
Dunkers et al [76] showed that by using dilute dichloromethane as a static modifier,
20–30 minute supercritical fluid extractions gave results comparable to those obtained
by conventional four-hour sampling methods in soil extractions.
Fahing et al [121] studied the effect of the addition of modifiers such as methanol
and water on the super-critical fluid extraction of organic solutes from soils and clays.
Hawthorne et al [4] compared the application of sub- and supercritical water in the
extractions of organics from soil, and found that both were effective extractants.
Hollender et al [125] compared the efficiencies of supercritical extraction, accelerated solvent extraction, Soxhlet, and ultrasonic extraction in the analysis of polycyclic
aromatic hydrocarbons in soils. Solvents with different polarity were used to extract
the PAHs from two soils, one with high and one with low contamination level.
Accelerated solvent extraction showed good results with all solvents almost independent of the solvent polarity and the best results were obtained with acetone-toluene
(1:1). Ultrasonic extraction with acetone-toluene for the uncontaminated soil and
acetone-ethanolamine was less effective. The PAH recovery obtained by supercritical fluid extraction was related to the soil matrix or the contamination level. The
best extraction conditions (CO 2 /10% pentane) are successful for the soil with a low
contamination level and a high acid content whereas the extractions of the highly
contaminated soil gave poor results irrespective of the solvent used.
REFERENCES
[1] Bowadt, S. & Hawthorne, S.B. (1995) Chromatography A, 703, 549.
[2] Deuster, R., Lubahn, N., Friedrich, C. & Kleiböhmer, W. (1997) Chromatography A,
785, 227.
[3] Richter, B.E., Jones, B.A., Ezzel, J.L., Poter, N.L., Avdalovic, N. & Phol, C. (1996)
Analytical Chemistry, 68, 1033.
moderately polar pesticides including triazines [116–117] sulphonyl areas [110–112],
organochlorine insecticides [111, 116], flumetron [110] and other herbicides [123].
An example of the application of supercritical carbon dioxide [114] and subcritical (hot) water extraction is the determination of the widely used pre-emergent
herbicide dacthal and its mono and diacid metabolites in soil. These compounds were
sequentially extracted from soils by first performing a supercritical hot water extract
for 15 minutes at 150
◦ C and 500 bar to recover dacthal, followed by a subcritical hot
water extraction to recover the metabolites, which were then trapped in-situ on a strong
anion exchange disc placed over the exit frit of the extraction cell. Dacthal was combined with the metabolites by placing the disc into a gas chromatograph autosampler
vial containing the supercritical fluid extract. The metabolites are then simultaneously
eluted from the disc and derivatised to their ethyl esters by reaction with ethyl iodide
at 100
◦ C. Meyer et al [120] showed that supercritical fluid extraction results can give
recoveries comparable to Soxhlet extraction methods, even for soils with high carbon contents McNally et al [103, 109] have studied factors affecting the supercritical
fluid extraction of soils. It was shown the soil type affects that recovery of moderately
polar analytes. In general the organic carbon content of the soil governs analytical
recovery.
Online coupling of supercritical fluid extraction and high-performance liquid chromatography considerably decreases sample preparation and analysis time [122, 123].
Dunkers et al [76] showed that by using dilute dichloromethane as a static modifier,
20–30 minute supercritical fluid extractions gave results comparable to those obtained
by conventional four-hour sampling methods in soil extractions.
Fahing et al [121] studied the effect of the addition of modifiers such as methanol
and water on the super-critical fluid extraction of organic solutes from soils and clays.
Hawthorne et al [4] compared the application of sub- and supercritical water in the
extractions of organics from soil, and found that both were effective extractants.
Hollender et al [125] compared the efficiencies of supercritical extraction, accelerated solvent extraction, Soxhlet, and ultrasonic extraction in the analysis of polycyclic
aromatic hydrocarbons in soils. Solvents with different polarity were used to extract
the PAHs from two soils, one with high and one with low contamination level.
Accelerated solvent extraction showed good results with all solvents almost independent of the solvent polarity and the best results were obtained with acetone-toluene
(1:1). Ultrasonic extraction with acetone-toluene for the uncontaminated soil and
acetone-ethanolamine was less effective. The PAH recovery obtained by supercritical fluid extraction was related to the soil matrix or the contamination level. The
best extraction conditions (CO 2 /10% pentane) are successful for the soil with a low
contamination level and a high acid content whereas the extractions of the highly
contaminated soil gave poor results irrespective of the solvent used.
REFERENCES
[1] Bowadt, S. & Hawthorne, S.B. (1995) Chromatography A, 703, 549.
[2] Deuster, R., Lubahn, N., Friedrich, C. & Kleiböhmer, W. (1997) Chromatography A,
785, 227.
[3] Richter, B.E., Jones, B.A., Ezzel, J.L., Poter, N.L., Avdalovic, N. & Phol, C. (1996)
Analytical Chemistry, 68, 1033.