Organic compounds in soils 15
with flame ionisation, electron capture and mass spectrometric detection. Benzenewater extractants were adjusted to pH4, 7 and 10 before the extraction in order to
selectively extract various types of acidic and basic organic compounds in addition to
hydrocarbons.
Thermal desorption mass spectrometry is a rapid technique for determining oil in
soils and sediments [29]. This method exhibited lower analytical variance compared
to Soxhlet extraction, i.e. followed by conventional analysis. The analysis time for wet
soil samples was about 20 minutes.
Weathering of aliphatic hydrocarbons
Risdon et al [30] have described a method for the determination of weathered n C 8
to n C 40 , hydrocarbons in soil. The method covers determination of total petroleum
hydrocarbons including diesel range compounds, kerosene range compounds and mineral oil range compounds in soils. Further modification to the carbon banding may
be made as requested for risk assessment. These include a series of ranges known as
Texas banding (from the Texas Risk Reduction Program) as well as separation of the
aliphatic and aromatic fractions. The method can be routinely used for measuring
hydrocarbons down to 10 mg kg
−1 in soil. Lower limits can be achieved by employing
a suitable solvent concentration step following extraction; however, this would result
in increased cycle time. Detection limits may vary for individual carbon ranges calculated on the percentage of the full range they cover. With an extraction efficiency and
recovery between less than 95% and 99%, this method can be easily positioned as a
good alternative to Soxhlet extraction and shows a good potential for implementation
as a standard method potentially providing further insight to the contaminated land
sector.
2.1.2 Aromatic hydrocarbons
Purge and trap gas chromatography
Kester et al [31] has discussed the application of purge and trap gas chromatography to
the determination of aromatic hydrocarbons such as benzene, ethyl benzene, toluenes
and xylene in soil. In this method, a 4 g portion of the soil is dispersed in methanol and
a methanoic surrogate spike containing deuterated compounds for mass spectrometric
recovery analysis are placed in 15 ml screw capped vial. Volatile compounds are dissolved in the solvent by shaking for 1 minute or by sonicating for 30 minutes. The slurry
is allowed to settle, centrifuging if necessary, and 10 to 100 µl aliquot of the extract
is added to organic-free water and dry pumped an ambient temperature into a Tenax
trap. The purge gases are analysed by gas chromatography using a photoionization
detector or can be analysed by mass spectrometry.
Pyrolysis gas chromatography-mass spectrometry
De Leeuw et al [32] have described a method based on Curie Point flash evaporationpyrolysis gas chromatography-mass spectrometry for the fast screening of anthropogenic aliphatic hydrocarbons in soils. The detection limit is in the low µg kg
−1 range.
Polycyclic aromatic hydrocarbons, heteroaromatic hydrocarbons and haloorganic
compounds and pyrolysis products of polymers can also be screened by this method.
with flame ionisation, electron capture and mass spectrometric detection. Benzenewater extractants were adjusted to pH4, 7 and 10 before the extraction in order to
selectively extract various types of acidic and basic organic compounds in addition to
hydrocarbons.
Thermal desorption mass spectrometry is a rapid technique for determining oil in
soils and sediments [29]. This method exhibited lower analytical variance compared
to Soxhlet extraction, i.e. followed by conventional analysis. The analysis time for wet
soil samples was about 20 minutes.
Weathering of aliphatic hydrocarbons
Risdon et al [30] have described a method for the determination of weathered n C 8
to n C 40 , hydrocarbons in soil. The method covers determination of total petroleum
hydrocarbons including diesel range compounds, kerosene range compounds and mineral oil range compounds in soils. Further modification to the carbon banding may
be made as requested for risk assessment. These include a series of ranges known as
Texas banding (from the Texas Risk Reduction Program) as well as separation of the
aliphatic and aromatic fractions. The method can be routinely used for measuring
hydrocarbons down to 10 mg kg
−1 in soil. Lower limits can be achieved by employing
a suitable solvent concentration step following extraction; however, this would result
in increased cycle time. Detection limits may vary for individual carbon ranges calculated on the percentage of the full range they cover. With an extraction efficiency and
recovery between less than 95% and 99%, this method can be easily positioned as a
good alternative to Soxhlet extraction and shows a good potential for implementation
as a standard method potentially providing further insight to the contaminated land
sector.
2.1.2 Aromatic hydrocarbons
Purge and trap gas chromatography
Kester et al [31] has discussed the application of purge and trap gas chromatography to
the determination of aromatic hydrocarbons such as benzene, ethyl benzene, toluenes
and xylene in soil. In this method, a 4 g portion of the soil is dispersed in methanol and
a methanoic surrogate spike containing deuterated compounds for mass spectrometric
recovery analysis are placed in 15 ml screw capped vial. Volatile compounds are dissolved in the solvent by shaking for 1 minute or by sonicating for 30 minutes. The slurry
is allowed to settle, centrifuging if necessary, and 10 to 100 µl aliquot of the extract
is added to organic-free water and dry pumped an ambient temperature into a Tenax
trap. The purge gases are analysed by gas chromatography using a photoionization
detector or can be analysed by mass spectrometry.
Pyrolysis gas chromatography-mass spectrometry
De Leeuw et al [32] have described a method based on Curie Point flash evaporationpyrolysis gas chromatography-mass spectrometry for the fast screening of anthropogenic aliphatic hydrocarbons in soils. The detection limit is in the low µg kg
−1 range.
Polycyclic aromatic hydrocarbons, heteroaromatic hydrocarbons and haloorganic
compounds and pyrolysis products of polymers can also be screened by this method.