Organic compounds in soils 39
Headspace analysis is the methods of choice for determining volatile organic [216–
223] in soil. A limitation of this method is incomplete desorption of the contaminants
in soil/water mixtures, but this problem can be overcome by the addition of methanol
to the sample [126, 129].
Stuart et al [220] studied the analysis of volatile organic compounds using an
automated static headspace method. Recoveries decreased in the following order:
water, pure sand, sandy soil, clay and topsoil. A full evaporation technique that
uses little or no aqueous phase and higher equilibration temperature gave the most
reproducible analyte recoveries.
Kawata et al [221] have described the effects of headspace conditions on recoveries
of volatile organic compounds from sediments and soil.
Papeafstathion and Luque de Castro et al [222] used pervaporation as an alternative to headspace analysis for the analysis of down to 1 ng/g of volatile organic
compounds in soils.
James and Stack et al [223] found that solid-phase microextraction is an effective
technique for determining volatile organic compounds in landfill sites. The headspace
above the sample was sampled.
Purge and trap analysis
The U.S. EPA-recommended method for measurement of trace levels of volatile organic
compounds in soil, namely purge-trap, measures the readily desorbable organic contaminants from soil pore spaces and external soil surfaces. It does not, however,
measure contamination that has diffused into internal microspores of soil matrix. Thus,
the purge-and-trap method measures only a small fraction of total soil contamination,
especially in long-contaminated soils, where ∼90–99% of contamination may be in
the interior of the soil matrix. Askari et al [225] compared three methods for determination of VOCs in aged field samples: purge-and-trap, methanol immersion, and
hot solvent extraction. Hot solvent extraction proved to be much more effective than
the U.S. EPA-approved purge-and-trap technique. For three long-contaminated soils
containing such volatile organic compounds as trichloroethylene, benzene, toluene,
chloroform, methylene chloride and cis-1, 1-dichloroethylene, recovery from purgeand-trap ranged between 1.5 and 41.3% that of hot solvent extraction. The data
obtained shows that purge-and-trap may not be the best methodology for measuring
soil volatile organic compound concentrations, particularly in aged soils. It is clear
from this and previous studies that the best overall choice for soil volatile organic
compounds measurements is hot solvent extraction. These results also indicate the
inefficiency of purge-and-trap as a method for evaluating vapour extraction remediation technology. These results suggest that the EPA should review the use of the
purge-and-trap method for measuring VOCs concentrations in soils.
Yang and Her et al [224] developed a rapid method for determination of
semivolatile compounds in contaminated soil samples by coupling solid-phase microextraction with attenuated total reflectance (ATR)-Fourier transform infrared (FT-IR)
spectroscopy. A trapezoidal internal reflection element was mounted horizontally in
a flow cell with the inlet port connected to a temperature-controlled glass extraction
chamber. Soil samples were placed inside the glass tube and heated to the desired
temperature. Vaporised semivolatile compounds were carried by a stream of nitrogen
Headspace analysis is the methods of choice for determining volatile organic [216–
223] in soil. A limitation of this method is incomplete desorption of the contaminants
in soil/water mixtures, but this problem can be overcome by the addition of methanol
to the sample [126, 129].
Stuart et al [220] studied the analysis of volatile organic compounds using an
automated static headspace method. Recoveries decreased in the following order:
water, pure sand, sandy soil, clay and topsoil. A full evaporation technique that
uses little or no aqueous phase and higher equilibration temperature gave the most
reproducible analyte recoveries.
Kawata et al [221] have described the effects of headspace conditions on recoveries
of volatile organic compounds from sediments and soil.
Papeafstathion and Luque de Castro et al [222] used pervaporation as an alternative to headspace analysis for the analysis of down to 1 ng/g of volatile organic
compounds in soils.
James and Stack et al [223] found that solid-phase microextraction is an effective
technique for determining volatile organic compounds in landfill sites. The headspace
above the sample was sampled.
Purge and trap analysis
The U.S. EPA-recommended method for measurement of trace levels of volatile organic
compounds in soil, namely purge-trap, measures the readily desorbable organic contaminants from soil pore spaces and external soil surfaces. It does not, however,
measure contamination that has diffused into internal microspores of soil matrix. Thus,
the purge-and-trap method measures only a small fraction of total soil contamination,
especially in long-contaminated soils, where ∼90–99% of contamination may be in
the interior of the soil matrix. Askari et al [225] compared three methods for determination of VOCs in aged field samples: purge-and-trap, methanol immersion, and
hot solvent extraction. Hot solvent extraction proved to be much more effective than
the U.S. EPA-approved purge-and-trap technique. For three long-contaminated soils
containing such volatile organic compounds as trichloroethylene, benzene, toluene,
chloroform, methylene chloride and cis-1, 1-dichloroethylene, recovery from purgeand-trap ranged between 1.5 and 41.3% that of hot solvent extraction. The data
obtained shows that purge-and-trap may not be the best methodology for measuring
soil volatile organic compound concentrations, particularly in aged soils. It is clear
from this and previous studies that the best overall choice for soil volatile organic
compounds measurements is hot solvent extraction. These results also indicate the
inefficiency of purge-and-trap as a method for evaluating vapour extraction remediation technology. These results suggest that the EPA should review the use of the
purge-and-trap method for measuring VOCs concentrations in soils.
Yang and Her et al [224] developed a rapid method for determination of
semivolatile compounds in contaminated soil samples by coupling solid-phase microextraction with attenuated total reflectance (ATR)-Fourier transform infrared (FT-IR)
spectroscopy. A trapezoidal internal reflection element was mounted horizontally in
a flow cell with the inlet port connected to a temperature-controlled glass extraction
chamber. Soil samples were placed inside the glass tube and heated to the desired
temperature. Vaporised semivolatile compounds were carried by a stream of nitrogen