240 Organic compounds in soils, sediments & sludges
of preconcentrating the organics in the sample, for example, by solvent extraction or
freeze drying a very large factor (10
4 –10
5 ) in order to achieve the required analytical
sensitivity. However, all earlier work suffered from the disadvantage that due to the
complexity of the gas chromatograms obtained and the inherent risks of relying on
retention data for component identification, many difficulties were encountered. Only
when capillary gas chromatography coupled with mass spectrometric identification
were introduced were the resolution and positive compound identification problems
made less formidable.
An early gas chromatographic method [207] used direct gas chromatography of
the sewage and achieved detection limits of only 0.2 g l
−1 . Baird et al [208] tabulated gas chromatography data on the occurrence of selected trace organics in sewage.
These include volatile halogenated organics, polynuclear hydrocarbons, chlorinated
pesticides and polychlorinated biphenyls. Preconcentration techniques include the use
of XAD-2 resins and ether-hexane extraction.
Roeraade et al [209] used continuous flow extraction of the sewage sample
together with on-line capillary gas chromatography to identify and determine organics.
Continuous extraction was performed in a fused silica capillary tube with n-pentane as
extractant, and phase separation using a semi-permeable PTFE membrane. The extract
flowed through a fused silica sample loop connected to a fused silica capillary column
or pre-column. Analysis was by gas chromatography with flame ionization detection
and the system was controlled by a programmable timer.
The system was evaluated using water samples containing aromatic and aliphatic
hydrocarbons, or trace amounts of a naphtha fraction, and samples from a municipal
sewage works. Results were comparable with those using a batch extraction procedure although better reproducibility was obtained with the flow extraction procedure.
Owing to absorption effects prior to extraction, a short length of capillary tubing was
recommended for connecting the sample and segmenting device.
The Water Research Centre [210] freeze dried 60 batches of sewage effluent to
produce a powder containing about 5% organic matter. This material was extracted
with various polar organic solvents and the extracts concentrated by evaporation. The
residues of organic matter extracted by each solvent were then treated with a suitable reagent in order to form the more volatile silyl derivatives (bis-(trimethylsiyl)
acetamine) of the reactive compounds present before injection into the gas chromatograph. Various fatty acids, cholesterol and coprostanol were determined by this
procedure.
Ellison and Wallbank et al [211] extended the technique slightly by applying
infrared and ultraviolet spectroscopy to solvent extracts of the sewage. However, this
finger-print approach to the problem frequently did not yield successful identifications
and lacked sensitivity.
10.9.2 Gas chromatography-mass spectrometry
Several works have discussed the application of this technique to the analysis of sewage
samples [212]. Warner et al [213] have described a systematic procedure for the determination of 54 semi-volatile organic constituents, designated as priority pollutants
in US federal regulations. The procedure involves extraction of the sludge sample
with methylene chloride or chloroform followed by column clean-up and detection of
of preconcentrating the organics in the sample, for example, by solvent extraction or
freeze drying a very large factor (10
4 –10
5 ) in order to achieve the required analytical
sensitivity. However, all earlier work suffered from the disadvantage that due to the
complexity of the gas chromatograms obtained and the inherent risks of relying on
retention data for component identification, many difficulties were encountered. Only
when capillary gas chromatography coupled with mass spectrometric identification
were introduced were the resolution and positive compound identification problems
made less formidable.
An early gas chromatographic method [207] used direct gas chromatography of
the sewage and achieved detection limits of only 0.2 g l
−1 . Baird et al [208] tabulated gas chromatography data on the occurrence of selected trace organics in sewage.
These include volatile halogenated organics, polynuclear hydrocarbons, chlorinated
pesticides and polychlorinated biphenyls. Preconcentration techniques include the use
of XAD-2 resins and ether-hexane extraction.
Roeraade et al [209] used continuous flow extraction of the sewage sample
together with on-line capillary gas chromatography to identify and determine organics.
Continuous extraction was performed in a fused silica capillary tube with n-pentane as
extractant, and phase separation using a semi-permeable PTFE membrane. The extract
flowed through a fused silica sample loop connected to a fused silica capillary column
or pre-column. Analysis was by gas chromatography with flame ionization detection
and the system was controlled by a programmable timer.
The system was evaluated using water samples containing aromatic and aliphatic
hydrocarbons, or trace amounts of a naphtha fraction, and samples from a municipal
sewage works. Results were comparable with those using a batch extraction procedure although better reproducibility was obtained with the flow extraction procedure.
Owing to absorption effects prior to extraction, a short length of capillary tubing was
recommended for connecting the sample and segmenting device.
The Water Research Centre [210] freeze dried 60 batches of sewage effluent to
produce a powder containing about 5% organic matter. This material was extracted
with various polar organic solvents and the extracts concentrated by evaporation. The
residues of organic matter extracted by each solvent were then treated with a suitable reagent in order to form the more volatile silyl derivatives (bis-(trimethylsiyl)
acetamine) of the reactive compounds present before injection into the gas chromatograph. Various fatty acids, cholesterol and coprostanol were determined by this
procedure.
Ellison and Wallbank et al [211] extended the technique slightly by applying
infrared and ultraviolet spectroscopy to solvent extracts of the sewage. However, this
finger-print approach to the problem frequently did not yield successful identifications
and lacked sensitivity.
10.9.2 Gas chromatography-mass spectrometry
Several works have discussed the application of this technique to the analysis of sewage
samples [212]. Warner et al [213] have described a systematic procedure for the determination of 54 semi-volatile organic constituents, designated as priority pollutants
in US federal regulations. The procedure involves extraction of the sludge sample
with methylene chloride or chloroform followed by column clean-up and detection of