Extraction of organic compounds from soil 7
passing the extract through a small disc of solid sorbent. The solid sorbents discussed to
date include carbon graphitised black [43] styrene-divinyl benzene [71], Carbograph-4
[74] and polyisobutylene [54].
An example of the application of subcritical water extraction-solid-phase microextraction is that of Crescenzi et al [69] (see above).
Water extraction is also occasionally combined with solid-phase microextraction.
Thus Wennrich et al [74] determined chlorophenols in soil by using accelerated water
extraction to remove the chlorophenols from the soil followed by adsorption onto a
solid sorbent for ten minutes at 125
◦ C. Low ppb detection limits were thus achieved.
Other applications of subcritical water extraction-solid-phase microextraction are
the determination of terbuthylazine and its metabolites [43] polycyclic aromatic hydrocarbons [71, 73] and polychlorobiphenyls [5]. Yang and Her et al [73] collected
1-chloronaphthylene, nitrobenzene and 2-chlorotoluene in soil on a hydrophobic polyisobutylene disc prior to analysis by attenuated total reflectance Fourier transform
infrared spectroscopy.
The toxic glycoalkaloids a-solanine and a-chaconine are produced in all parts of
the plant, and post-harvest potato tubers may represent a source of soil and water
contamination. Jensen et al [124] developed a method for extraction and purification
of a-solanine in soil samples. Soil samples were extracted with tetrahydrofuran, water,
acrylonitrile acetic acid (50:30:20:1) and the extract purified by SPE before HPLC
determination of a-solanine. The limit of detection was 2.4 mg, of a-solanine kg soil.
The procedure was used for determination of a-solanine in spiked soils with varying
content of organic matter and texture. Recovery for soil samples spiked with a-solanine
1 h before extraction was 61–68% for soils low in organic carbon (<2.2% C), and to
47% for soil high in organic carbon. Similar recoveries were obtained for a-chaconine.
The reproducibility of the method shown by the relative standard deviation varied
from 1.7 to 10.1% depending on the soil type. No decrease in extractable a-solanine
was observed until day 17 for soil samples spiked with a pure a-solanine kept at 5
◦ C,
while the content in samples spiked with potato materials showed a faster decline.
This indicates that the degradation and/or ageing processes proceed relatively slowly
for glycoalkaloids in soil matrices.
1.7 SUPERCRITICAL FLUID EXTRACTION
This is an attractive technique for recovering organic compounds from soils. Carbon
dioxide is currently the fluid of choice, due to its low toxicity and environmental acceptability. The physicochemical properties of supercritical fluids, including low viscosity,
variable solvent strength and high diffusivity, contributes to faster extractions compared to conventional extraction techniques such as Soxhlet extraction or sonication.
Supercritical fluid extraction methods have been successfully developed for nonpolar
compounds that exhibit solubilities in carbon dioxide, such as aromatic compounds
[76–82], polychloro biphenyls, triacryl chlorodioxins [82–90] and trialkyl phosphates
[94], amines [92], pyridinel [93, 94], hydrocarbons [95], volatile organic compounds
[96–99], phenols [100], organic acids [101], entero viruses [104], organochlorine pesticides [103] and miscellaneous herbroides and pesticides [104–114]. With methanol
as modifier, supercritical carbon dioxide becomes more amenable to the extraction of
passing the extract through a small disc of solid sorbent. The solid sorbents discussed to
date include carbon graphitised black [43] styrene-divinyl benzene [71], Carbograph-4
[74] and polyisobutylene [54].
An example of the application of subcritical water extraction-solid-phase microextraction is that of Crescenzi et al [69] (see above).
Water extraction is also occasionally combined with solid-phase microextraction.
Thus Wennrich et al [74] determined chlorophenols in soil by using accelerated water
extraction to remove the chlorophenols from the soil followed by adsorption onto a
solid sorbent for ten minutes at 125
◦ C. Low ppb detection limits were thus achieved.
Other applications of subcritical water extraction-solid-phase microextraction are
the determination of terbuthylazine and its metabolites [43] polycyclic aromatic hydrocarbons [71, 73] and polychlorobiphenyls [5]. Yang and Her et al [73] collected
1-chloronaphthylene, nitrobenzene and 2-chlorotoluene in soil on a hydrophobic polyisobutylene disc prior to analysis by attenuated total reflectance Fourier transform
infrared spectroscopy.
The toxic glycoalkaloids a-solanine and a-chaconine are produced in all parts of
the plant, and post-harvest potato tubers may represent a source of soil and water
contamination. Jensen et al [124] developed a method for extraction and purification
of a-solanine in soil samples. Soil samples were extracted with tetrahydrofuran, water,
acrylonitrile acetic acid (50:30:20:1) and the extract purified by SPE before HPLC
determination of a-solanine. The limit of detection was 2.4 mg, of a-solanine kg soil.
The procedure was used for determination of a-solanine in spiked soils with varying
content of organic matter and texture. Recovery for soil samples spiked with a-solanine
1 h before extraction was 61–68% for soils low in organic carbon (<2.2% C), and to
47% for soil high in organic carbon. Similar recoveries were obtained for a-chaconine.
The reproducibility of the method shown by the relative standard deviation varied
from 1.7 to 10.1% depending on the soil type. No decrease in extractable a-solanine
was observed until day 17 for soil samples spiked with a pure a-solanine kept at 5
◦ C,
while the content in samples spiked with potato materials showed a faster decline.
This indicates that the degradation and/or ageing processes proceed relatively slowly
for glycoalkaloids in soil matrices.
1.7 SUPERCRITICAL FLUID EXTRACTION
This is an attractive technique for recovering organic compounds from soils. Carbon
dioxide is currently the fluid of choice, due to its low toxicity and environmental acceptability. The physicochemical properties of supercritical fluids, including low viscosity,
variable solvent strength and high diffusivity, contributes to faster extractions compared to conventional extraction techniques such as Soxhlet extraction or sonication.
Supercritical fluid extraction methods have been successfully developed for nonpolar
compounds that exhibit solubilities in carbon dioxide, such as aromatic compounds
[76–82], polychloro biphenyls, triacryl chlorodioxins [82–90] and trialkyl phosphates
[94], amines [92], pyridinel [93, 94], hydrocarbons [95], volatile organic compounds
[96–99], phenols [100], organic acids [101], entero viruses [104], organochlorine pesticides [103] and miscellaneous herbroides and pesticides [104–114]. With methanol
as modifier, supercritical carbon dioxide becomes more amenable to the extraction of