214 Organic compounds in soils, sediments & sludges
Miscellaneous
The UK Department of the Environment standard has published methods [6] involving
carbon tetrachloride extraction for the determination of the extractable hydrocarbon
oils and greases in sewage. The first method consists of solvent extraction using carbon
tetrachloride following by gravimetric determination of the extractable material. The
second method partially fractionates this material according to the type of material
using chromatographic techniques. Separation on a silica gel column with an upper
layer of Florasil is used to remove aromatic and polar compounds respectively, while
the eluate contains the aliphatic hydrocarbon ingredients.
10.1.2 Polycyclic aromatic hydrocarbons
Trably et al [7] has developed statistical tools for the optimisation of a very reproductable method for the analysis of polycyclic aromatic hydrocarbons in sludge
samples.
The aim of this study was to develop and optimise an analytical method for the
determination of 14 priority polycyclic aromatic compounds in sludge samples based
on accelerated solvent extraction coupled to RP-HPLC/fluorescence detection. Statistical tools were used to demonstrate the influence of the parameters during the
optimisation steps. The final parameters were selected to provide analytical errors statistically as low as possible. First, couples of excitation/emission detection wavelength
were tested and some were finally selected to provide errors lower than 2%. It was
then demonstrated that polycyclic aromatic hydro extraction efficiencies are not statistically influenced by the polycyclic aromatic compound parameters. It was also found
that the polycyclic aromatichydro compound extraction from sludge samples provides
statistically similar results to those obtained with traditional Soxhlet extraction, but
with a lower reproducibility error. After optimisation, the accuracy of the method
was validated with a certified sludge. An optimised analytical procedure is proposed
to monitor polycyclic aromatic hydrocarbons during lab-scale experiments requiring
highly repeatable and accurate results from a low sample volume contaminated by
polycyclic aromatic hydrocarbons at trace levels.
Figure 10.1 shows the polycyclic aromatic hydrocarbons chromatograms
obtained. The PAH peaks can be readily identified either in the standard solution
or in the sludge extract. The chromatograms exhibit only a few interfering peaks due
to the high specificity of the fluorescence detection in contract with mass-spectrometry
detection chromatograms.
High performance liquid chromatography
This technique has been applied to the determination of polycyclic aromatic hydrocarbons in sewage amounts down to 2 µg L
−1 [8–10].
Sweetman et al [10] has described a method based on steam distillation coupled
with HPLC fraction and GC FID for the determination of n-alkanes, linear alkyl benzenes, polycyclic aromatic hydrocarbons and 4-nonylphenol in digested sewage sludge.
Bersek et al [11] used supercritical fluid extraction to extract polycyclic aromatic hydrocarbons, polychloro biphenyls and organochlorine pesticides in sewage
sludge, supercritical fluid extraction was efficient, fast and partially selective in this
application.
Miscellaneous
The UK Department of the Environment standard has published methods [6] involving
carbon tetrachloride extraction for the determination of the extractable hydrocarbon
oils and greases in sewage. The first method consists of solvent extraction using carbon
tetrachloride following by gravimetric determination of the extractable material. The
second method partially fractionates this material according to the type of material
using chromatographic techniques. Separation on a silica gel column with an upper
layer of Florasil is used to remove aromatic and polar compounds respectively, while
the eluate contains the aliphatic hydrocarbon ingredients.
10.1.2 Polycyclic aromatic hydrocarbons
Trably et al [7] has developed statistical tools for the optimisation of a very reproductable method for the analysis of polycyclic aromatic hydrocarbons in sludge
samples.
The aim of this study was to develop and optimise an analytical method for the
determination of 14 priority polycyclic aromatic compounds in sludge samples based
on accelerated solvent extraction coupled to RP-HPLC/fluorescence detection. Statistical tools were used to demonstrate the influence of the parameters during the
optimisation steps. The final parameters were selected to provide analytical errors statistically as low as possible. First, couples of excitation/emission detection wavelength
were tested and some were finally selected to provide errors lower than 2%. It was
then demonstrated that polycyclic aromatic hydro extraction efficiencies are not statistically influenced by the polycyclic aromatic compound parameters. It was also found
that the polycyclic aromatichydro compound extraction from sludge samples provides
statistically similar results to those obtained with traditional Soxhlet extraction, but
with a lower reproducibility error. After optimisation, the accuracy of the method
was validated with a certified sludge. An optimised analytical procedure is proposed
to monitor polycyclic aromatic hydrocarbons during lab-scale experiments requiring
highly repeatable and accurate results from a low sample volume contaminated by
polycyclic aromatic hydrocarbons at trace levels.
Figure 10.1 shows the polycyclic aromatic hydrocarbons chromatograms
obtained. The PAH peaks can be readily identified either in the standard solution
or in the sludge extract. The chromatograms exhibit only a few interfering peaks due
to the high specificity of the fluorescence detection in contract with mass-spectrometry
detection chromatograms.
High performance liquid chromatography
This technique has been applied to the determination of polycyclic aromatic hydrocarbons in sewage amounts down to 2 µg L
−1 [8–10].
Sweetman et al [10] has described a method based on steam distillation coupled
with HPLC fraction and GC FID for the determination of n-alkanes, linear alkyl benzenes, polycyclic aromatic hydrocarbons and 4-nonylphenol in digested sewage sludge.
Bersek et al [11] used supercritical fluid extraction to extract polycyclic aromatic hydrocarbons, polychloro biphenyls and organochlorine pesticides in sewage
sludge, supercritical fluid extraction was efficient, fast and partially selective in this
application.