Organic compounds in soils 29
and for domestic purposes for over 50 years. It is well-known that chlorophenols are
toxic at low levels. The more highly chlorinated phenols such as trichlorophenols and
pentachlorophenol are also persistent. Five of the chlorophenols (2-chlorophenol, 2,4dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) have been classified as priority pollutants by the US Environmental Protection
Agency (EPA).
Determining chlorophenols in soil samples usually involves various methods of
liquid-solid extraction, e.g. Soxhlet [137, 138], microwave- or ultrasonically assisted
[139], and accelerated solvent (ASE) [140] extraction with an organic solvent or solvent
mixture followed by both clean-up and preconcentration procedures and subcritical
hot water extraction [141–143].
Wennrich et al [144] investigated the capabilities of coupling accelerated solvent
extraction with water as the extraction solvent and solid-phase microextraction to
determine chlorophenols in polluted soils. Subcritical water extraction was performed
using a commercially available accelerated solvent extractor. This system solves the
problem of the analytes partitioning back to the soil matrix, which can occur in
straightforward subcritical water extraction because in the Wennrich et al method
[144] the aqueous phase and the soil are separated under the extraction conditions.
Gas chromatography-mass spectrometry
Stable-isotope dilution analysis is an analytical technique in which a known quantity of
a stable-labelled isotope is added to a sample prior to extraction, in order to quantitate
a particular compound. The ratio of the naturally abundant and the stable-labelled
isotope is a measure of the naturally abundant compound and can be determined
only by gas chromatography-mass spectrometry since the naturally abundant and the
stable-labelled isotope cannot be completely separated gas chromatographically.
Lopez-Avila et al [145] used a stable isotope dilution gas chromatography-mass
spectrometry technique to determine down to 0.1 ppb of pentachlorophenol (also
atrazine, diazinon and lindane) in soil. Soil samples are extracted with acetone and
hexane, Analysis is performed by high-resolution gas chromatography-mass spectrometry with the mass spectrometer operated in the selected ion monitoring mode. An
accuracy greater than 86% and a precision of better than 8% were demonstrated by
use of spiked samples.
Renberg et al [146] used an ion exchange technique for the determination of
chlorophenols and phenoxyacetic acid herbicides in soil. In this method, the soil
extracts are mixed with Sephadex AQE A-25 anion exchanger and the adsorbed
materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl
or 2-chloroethyl esters for stable isotope dilution gas chromatography. Recoveries
for 2,3,6 trichlorophenol 2,3,4,6 tetrachlorophenol and pentachlorophenol from
fortified samples exceed 97%.
The total acquisition times, total scan times and the dwell times for the various
ions mentioned are shown in Table 2.3.
A method based on spectrophotometry has also been used for the determination
of pentachlorophenol in soil [121].
and for domestic purposes for over 50 years. It is well-known that chlorophenols are
toxic at low levels. The more highly chlorinated phenols such as trichlorophenols and
pentachlorophenol are also persistent. Five of the chlorophenols (2-chlorophenol, 2,4dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) have been classified as priority pollutants by the US Environmental Protection
Agency (EPA).
Determining chlorophenols in soil samples usually involves various methods of
liquid-solid extraction, e.g. Soxhlet [137, 138], microwave- or ultrasonically assisted
[139], and accelerated solvent (ASE) [140] extraction with an organic solvent or solvent
mixture followed by both clean-up and preconcentration procedures and subcritical
hot water extraction [141–143].
Wennrich et al [144] investigated the capabilities of coupling accelerated solvent
extraction with water as the extraction solvent and solid-phase microextraction to
determine chlorophenols in polluted soils. Subcritical water extraction was performed
using a commercially available accelerated solvent extractor. This system solves the
problem of the analytes partitioning back to the soil matrix, which can occur in
straightforward subcritical water extraction because in the Wennrich et al method
[144] the aqueous phase and the soil are separated under the extraction conditions.
Gas chromatography-mass spectrometry
Stable-isotope dilution analysis is an analytical technique in which a known quantity of
a stable-labelled isotope is added to a sample prior to extraction, in order to quantitate
a particular compound. The ratio of the naturally abundant and the stable-labelled
isotope is a measure of the naturally abundant compound and can be determined
only by gas chromatography-mass spectrometry since the naturally abundant and the
stable-labelled isotope cannot be completely separated gas chromatographically.
Lopez-Avila et al [145] used a stable isotope dilution gas chromatography-mass
spectrometry technique to determine down to 0.1 ppb of pentachlorophenol (also
atrazine, diazinon and lindane) in soil. Soil samples are extracted with acetone and
hexane, Analysis is performed by high-resolution gas chromatography-mass spectrometry with the mass spectrometer operated in the selected ion monitoring mode. An
accuracy greater than 86% and a precision of better than 8% were demonstrated by
use of spiked samples.
Renberg et al [146] used an ion exchange technique for the determination of
chlorophenols and phenoxyacetic acid herbicides in soil. In this method, the soil
extracts are mixed with Sephadex AQE A-25 anion exchanger and the adsorbed
materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl
or 2-chloroethyl esters for stable isotope dilution gas chromatography. Recoveries
for 2,3,6 trichlorophenol 2,3,4,6 tetrachlorophenol and pentachlorophenol from
fortified samples exceed 97%.
The total acquisition times, total scan times and the dwell times for the various
ions mentioned are shown in Table 2.3.
A method based on spectrophotometry has also been used for the determination
of pentachlorophenol in soil [121].