Organic compounds in soils 41
87% using headspace gas chromatography. Levels of trifluoracetic acid in soil down
to 0.2 ng/g can be determined by the procedure.
Yang and Chen et al [239] constructed a reflection-absorption infrared sensing
device for the detection of semi-volatile aromatic compounds in soils.
Hiatt et al [238] shows that the role of internal standards of their interaction
with soils have an impact on the accuracy of volatile organics determinations. The
workers describe an IR-sensing device for the examination of chlorinated aromatic
compounds in soils. To prepare this sensing device, a 20-mL glass vial modified for
use in the analysis of soil samples by conventional Fourier-transform infrared (FT-IR)
spectroscopy. In this sampling device, an aluminium plate coated with a hydrophobic film was placed on top of the cap of the sample vial to absorb the analytes that
evaporated from the soil matrix. After this absorption process was complete, the cap
was placed in an FT-IR spectrometer, and the absorbed analytes were detected in the
reflection-absorption (RA) mode. To accelerate the rate of evaporation of the analytes,
the soil samples were heated to various temperatures. Other factors, such as the moisture content, sampling time, thickness of the hydrophobic film, and the volatilities
and concentrations of the analytes, were also examined to optimise the analytical conditions. The results indicated that the time required to reach equilibrium conditions
was short, and evaporation/absorption could be achieved within 10 min. With a water
content of 10% (v/w) or less, the intensities of the analytical signals were increased
greatly when compared with those of dry samples; when the water content was above
10% (v/w), these intensities decreased, partially as a result of the heating efficiency.
After examining the compounds that had different vapour pressures, the analytical
results indicated that this method was applicable to the examination of compounds
that had vapour pressures below 1.0 Torr. Using the optimal conditions determined in
this study, the detection limits for semivolatile aromatic compounds were lower than
100 ng/g, and the regression coefficients of the standard curves for compounds that
had a vapour pressure lower than 1.0 Torr were larger than 0.99 in the concentration
range of 1–100 µg/g.
2.7 POLYCHLORODIBENZO-p-DIOXINS
AND POLYCHLORODIBENZOFURANS
Polychlorodibenzo dibenzo-p-dioxins, polychlorinated dibenzofurans and orthounsubstantiated polychlorinated biphenyls (non-ortho polychlorobiphenyls) are three
structurally and toxicologically related families of anthropogenic chemical compounds
that have in recent years been shown to have the potential to cause serious environmental contamination due to their extreme toxicities [240–245]. These substances are
trace-levels components or by-products in several large-volume and widely used synthetic chemicals, principally polychlorobiphenyls and chlorinated phenols [246, 247]
and can also be produced during combustion processes [248–250] and by photolysis
[251, 252]. In general, polychlorodibenzo-p-dioxins and dibenzofurans and non-ortho
polychlorobiphenyls are classified as highly toxic substances [253] although the toxicities are dramatically dependent on the number of positions of the chlorine substituents
[254]. About ten individual members of a total of 216 polychlorodibenzo-p-dioxins
87% using headspace gas chromatography. Levels of trifluoracetic acid in soil down
to 0.2 ng/g can be determined by the procedure.
Yang and Chen et al [239] constructed a reflection-absorption infrared sensing
device for the detection of semi-volatile aromatic compounds in soils.
Hiatt et al [238] shows that the role of internal standards of their interaction
with soils have an impact on the accuracy of volatile organics determinations. The
workers describe an IR-sensing device for the examination of chlorinated aromatic
compounds in soils. To prepare this sensing device, a 20-mL glass vial modified for
use in the analysis of soil samples by conventional Fourier-transform infrared (FT-IR)
spectroscopy. In this sampling device, an aluminium plate coated with a hydrophobic film was placed on top of the cap of the sample vial to absorb the analytes that
evaporated from the soil matrix. After this absorption process was complete, the cap
was placed in an FT-IR spectrometer, and the absorbed analytes were detected in the
reflection-absorption (RA) mode. To accelerate the rate of evaporation of the analytes,
the soil samples were heated to various temperatures. Other factors, such as the moisture content, sampling time, thickness of the hydrophobic film, and the volatilities
and concentrations of the analytes, were also examined to optimise the analytical conditions. The results indicated that the time required to reach equilibrium conditions
was short, and evaporation/absorption could be achieved within 10 min. With a water
content of 10% (v/w) or less, the intensities of the analytical signals were increased
greatly when compared with those of dry samples; when the water content was above
10% (v/w), these intensities decreased, partially as a result of the heating efficiency.
After examining the compounds that had different vapour pressures, the analytical
results indicated that this method was applicable to the examination of compounds
that had vapour pressures below 1.0 Torr. Using the optimal conditions determined in
this study, the detection limits for semivolatile aromatic compounds were lower than
100 ng/g, and the regression coefficients of the standard curves for compounds that
had a vapour pressure lower than 1.0 Torr were larger than 0.99 in the concentration
range of 1–100 µg/g.
2.7 POLYCHLORODIBENZO-p-DIOXINS
AND POLYCHLORODIBENZOFURANS
Polychlorodibenzo dibenzo-p-dioxins, polychlorinated dibenzofurans and orthounsubstantiated polychlorinated biphenyls (non-ortho polychlorobiphenyls) are three
structurally and toxicologically related families of anthropogenic chemical compounds
that have in recent years been shown to have the potential to cause serious environmental contamination due to their extreme toxicities [240–245]. These substances are
trace-levels components or by-products in several large-volume and widely used synthetic chemicals, principally polychlorobiphenyls and chlorinated phenols [246, 247]
and can also be produced during combustion processes [248–250] and by photolysis
[251, 252]. In general, polychlorodibenzo-p-dioxins and dibenzofurans and non-ortho
polychlorobiphenyls are classified as highly toxic substances [253] although the toxicities are dramatically dependent on the number of positions of the chlorine substituents
[254]. About ten individual members of a total of 216 polychlorodibenzo-p-dioxins