218 Organic compounds in soils, sediments & sludges
Standard Method [30]. The total amount of organic acids determined according to the
Standard Method is higher than that found by the Narkis and Henfield-Furie method.
On average between 85 and 98% of the organic acids determined by the standard
methods procedure were found to be volatile acids by the direct injection method.
Abbaticchio et al [31] have described a procedure for the determination of individual volatile fatty acids in sewage, which overcomes problems associated with direct
aqueous injections on a gas chromatograph, such as frequent cleaning, column ageing and flame ionisation detection. The chromatographic determination is preceded by
steam distillation. The recoveries for volatile fatty acid concentrations of 50–200 mg l
−1
were 97.6–99.0% and almost stoichiometric. The precision and accuracy of the method
are good.
Salicyclic acid has been determined in sewage works effluent [32]. Abel et al [33]
determined nonyl phenoxy carboxylic acids in sewage effluent by high resolution gas
chromatography-mass spectrometry and high performance liquid chromatography.
The predominant compounds were nonyl (phenoxy) acetic acid. Nonyl(phenoxy)
(ethoxy) acetic acid concentrations down to 1 µg l
−1 could be determined.
Column chromatography
Methods have been described for the determination of total fatty acids in raw sewage
sludge. These methods [34–36] require a concentration step such as simple distillation,
steam distillation, evaporation, or extraction [37–39] which resulted in great losses of
the volatile matter [40–41].
Straight distillation or steam distillation of volatile acids and the chromatographic
separation have been proposed in Standard Methods [30] for the organic acids in
sludge. In this method an acidified aqueous sample, containing relatively high concentrations of organic acids, is adsorbed on a column of silicic acid and the acids are eluted
with n-butanol in chloroform. The elute is collected and titrated with standard base. All
short chain (1–6 carbon) organic acids are eluted, but so are crotonic, adipic, pyruvic,
phthalic, fumaric, lactic, succinic, malonic, aconitic and oxalic acids, as well as alkyl
sulphates and alkyl-aryl sulphonates. No information on the individual volatile acids is
obtained by the method and the results are reported collectively as total organic acids.
Various chromatographic methods, such as paper [39, 40], and gel chromatography
[36], have been used for the analysis of sludge digester liquor. Mueller et al [41] have
modified the indirect chromatographic method for samples of raw sewage and river
water involving tedious concentration steps, leading to losses. In paper chromatography individual volatile acid concentrations should be higher than 600 mg L
−1 , while
in other methods the minimum detectable level is 1000 mg L
−1 [42, 43].
Peu et al [44] developed a method based on high performance liquid chromatography for the determination of volatile fatty acids in pig slurry. The acids are isolated
with a cation column for carbohydrates using an isocratic phosphate eluent coupled with an ultraviolet detector in series. Centrifuged and filtered samples can be
injected directly into the liquid chromatographic system. The accuracy of this liquidchromatographic procedure using spiked solutions ranging between 20 and 5000 mg/L
of volatile fatty acid standard solution varied from 87 to 124%. The precision of the
procedure, expressed as variability, was between 9.2 and 0.6% for a spiked solution
concentration of 20 and 5000 mg/L, respectively.
Standard Method [30]. The total amount of organic acids determined according to the
Standard Method is higher than that found by the Narkis and Henfield-Furie method.
On average between 85 and 98% of the organic acids determined by the standard
methods procedure were found to be volatile acids by the direct injection method.
Abbaticchio et al [31] have described a procedure for the determination of individual volatile fatty acids in sewage, which overcomes problems associated with direct
aqueous injections on a gas chromatograph, such as frequent cleaning, column ageing and flame ionisation detection. The chromatographic determination is preceded by
steam distillation. The recoveries for volatile fatty acid concentrations of 50–200 mg l
−1
were 97.6–99.0% and almost stoichiometric. The precision and accuracy of the method
are good.
Salicyclic acid has been determined in sewage works effluent [32]. Abel et al [33]
determined nonyl phenoxy carboxylic acids in sewage effluent by high resolution gas
chromatography-mass spectrometry and high performance liquid chromatography.
The predominant compounds were nonyl (phenoxy) acetic acid. Nonyl(phenoxy)
(ethoxy) acetic acid concentrations down to 1 µg l
−1 could be determined.
Column chromatography
Methods have been described for the determination of total fatty acids in raw sewage
sludge. These methods [34–36] require a concentration step such as simple distillation,
steam distillation, evaporation, or extraction [37–39] which resulted in great losses of
the volatile matter [40–41].
Straight distillation or steam distillation of volatile acids and the chromatographic
separation have been proposed in Standard Methods [30] for the organic acids in
sludge. In this method an acidified aqueous sample, containing relatively high concentrations of organic acids, is adsorbed on a column of silicic acid and the acids are eluted
with n-butanol in chloroform. The elute is collected and titrated with standard base. All
short chain (1–6 carbon) organic acids are eluted, but so are crotonic, adipic, pyruvic,
phthalic, fumaric, lactic, succinic, malonic, aconitic and oxalic acids, as well as alkyl
sulphates and alkyl-aryl sulphonates. No information on the individual volatile acids is
obtained by the method and the results are reported collectively as total organic acids.
Various chromatographic methods, such as paper [39, 40], and gel chromatography
[36], have been used for the analysis of sludge digester liquor. Mueller et al [41] have
modified the indirect chromatographic method for samples of raw sewage and river
water involving tedious concentration steps, leading to losses. In paper chromatography individual volatile acid concentrations should be higher than 600 mg L
−1 , while
in other methods the minimum detectable level is 1000 mg L
−1 [42, 43].
Peu et al [44] developed a method based on high performance liquid chromatography for the determination of volatile fatty acids in pig slurry. The acids are isolated
with a cation column for carbohydrates using an isocratic phosphate eluent coupled with an ultraviolet detector in series. Centrifuged and filtered samples can be
injected directly into the liquid chromatographic system. The accuracy of this liquidchromatographic procedure using spiked solutions ranging between 20 and 5000 mg/L
of volatile fatty acid standard solution varied from 87 to 124%. The precision of the
procedure, expressed as variability, was between 9.2 and 0.6% for a spiked solution
concentration of 20 and 5000 mg/L, respectively.