38 Organic compounds in soils, sediments & sludges
and may pose serious health risks. The main emission sources of volatile organic
compounds are industry, traffic and energy production. Serious local contamination
problems often follow from accidents, leakage of petrol and diesel fuel from underground storage tanks, and improper waste treatment. Volatile organic compounds
in soil easily diffuse from the point of emission over wide areas, finding their ways
into groundwater [224] and, through construction or sewerage, into households [225,
226]. The contamination of groundwater is becoming one of the most serious environmental problems. Several water catchments have already had to be closed because
of high concentrations of volatile organic compounds or other organic contaminants.
Intensified research and reconditioning of contaminated areas are needed, as well as
continuous monitoring of the quality of drinking water.
Ultrasonic extraction, methanol extraction [227] and supercritical fluid extraction
have all been applied to the extraction of or the determination of volatile organic
compounds [228, 229] in soils. However, methods based on headspace analysis, purge
and trap analysis or on mass spectrometry are now the methods of choice.
Headspace analysis
Both direct vapour partitioning and solvent extraction methods of sample preparation are commonly used for the characterisation of volatile organic compounds
(VOCs) in soil. These two approaches of recovering VOCs from this matrix, and
other forms of solid waste, are often used interchangeably without any recognition
of how different parameters (environmental and procedural) influence their performance. Hewitt et al [214] compared sample preparation commonly used for the
partitioning headspace methods and three solvent extraction methods of preparing
soil samples for the determination of VOCs without being confounded by volatilisation or biodegradation losses. Soil samples were spiked with five aromatic and four
chlorinated compounds using two different laboratory procedures. Recovery efficiencies for the preparation methods tested depended on soil organic carbon content, the
Octanol-water partition coefficients of specific analytes, and the duration of solvent
extraction. Overall, methanol extraction was the most efficient and robust method for
recovering spiked VOCs. Recovery of VOCs with tetraethylene glycol dimethyl ether
and poly(propylene)glycol, as well as three vapour partitioning headspace methods,
were frequently less than that obtained with methanol.
A combination of headspace sampling and liquid phase microextraction (LPME)
has been successfully developed to solve sensitivity problems in attenuated total
reflection (ATR) infrared determination of volatile compounds (VOCs) [215]. The
headspace sampling facilitates the selective extraction of the target volatile analytes
from the sample matrix, while the liquid phase microextraction allows their preconcentration prior to infrared analysis. The direct determination of extracted analytes
in the acceptor solvent provides high preconcentration factors of the order of 200
with a reduced consumption of organic solvents and a minimum generation of wastes.
The qualitative and quantitative capability of the proposed approach was evaluated
on the basis of two different examples: (i) screening of benzene, toluene and xylene
compounds in soil samples and (ii) quantitative determination of toluene in cosmetic
nail products.
and may pose serious health risks. The main emission sources of volatile organic
compounds are industry, traffic and energy production. Serious local contamination
problems often follow from accidents, leakage of petrol and diesel fuel from underground storage tanks, and improper waste treatment. Volatile organic compounds
in soil easily diffuse from the point of emission over wide areas, finding their ways
into groundwater [224] and, through construction or sewerage, into households [225,
226]. The contamination of groundwater is becoming one of the most serious environmental problems. Several water catchments have already had to be closed because
of high concentrations of volatile organic compounds or other organic contaminants.
Intensified research and reconditioning of contaminated areas are needed, as well as
continuous monitoring of the quality of drinking water.
Ultrasonic extraction, methanol extraction [227] and supercritical fluid extraction
have all been applied to the extraction of or the determination of volatile organic
compounds [228, 229] in soils. However, methods based on headspace analysis, purge
and trap analysis or on mass spectrometry are now the methods of choice.
Headspace analysis
Both direct vapour partitioning and solvent extraction methods of sample preparation are commonly used for the characterisation of volatile organic compounds
(VOCs) in soil. These two approaches of recovering VOCs from this matrix, and
other forms of solid waste, are often used interchangeably without any recognition
of how different parameters (environmental and procedural) influence their performance. Hewitt et al [214] compared sample preparation commonly used for the
partitioning headspace methods and three solvent extraction methods of preparing
soil samples for the determination of VOCs without being confounded by volatilisation or biodegradation losses. Soil samples were spiked with five aromatic and four
chlorinated compounds using two different laboratory procedures. Recovery efficiencies for the preparation methods tested depended on soil organic carbon content, the
Octanol-water partition coefficients of specific analytes, and the duration of solvent
extraction. Overall, methanol extraction was the most efficient and robust method for
recovering spiked VOCs. Recovery of VOCs with tetraethylene glycol dimethyl ether
and poly(propylene)glycol, as well as three vapour partitioning headspace methods,
were frequently less than that obtained with methanol.
A combination of headspace sampling and liquid phase microextraction (LPME)
has been successfully developed to solve sensitivity problems in attenuated total
reflection (ATR) infrared determination of volatile compounds (VOCs) [215]. The
headspace sampling facilitates the selective extraction of the target volatile analytes
from the sample matrix, while the liquid phase microextraction allows their preconcentration prior to infrared analysis. The direct determination of extracted analytes
in the acceptor solvent provides high preconcentration factors of the order of 200
with a reduced consumption of organic solvents and a minimum generation of wastes.
The qualitative and quantitative capability of the proposed approach was evaluated
on the basis of two different examples: (i) screening of benzene, toluene and xylene
compounds in soil samples and (ii) quantitative determination of toluene in cosmetic
nail products.