252 Organic compounds in soils, sediments & sludges
is discussed. The main organotin compounds detected in various samples are butylins;
cyclohexyl- and phenyltins were identified in some of the sediment and sewage sludge
samples. Methylbutyltins and tetrabutyltin were not detected. Concentrations were
found to be in a low mg kg
−1 range in sewage sludge.
Miscellaneous
A standard UK procedure discusses the determination of organic, inorganic and total
tin in sludges and sediments [3].
11.3 ORGANOMERCURY COMPOUNDS
Van Ettekoven et al [4] has described a direct semi-automatic scheme based on ultraviolet light absorption for the determination of total mercury in water and sewage sludge.
The full determination is about 10 minutes. The lower limit of detection of mercury
in water is 0.03 µg L
−1 and 0.2 mg L
−1 (mg kg
−1 dry matter) in sewage sludge.
The Department of the Environment (UK) [5] has described a method for determining total organic plus inorganic mercury in non-saline sewage and effluents. All
forms of mercury are converted to inorganic mercury using prolonged oxidation with
potassium permanganage [9]. Solid samples require a more prolonged and vigorous
oxidation to bring the mercury completely into solution in the organic form. A modification of the Uthe digestion procedure is used for such samples [10]. The inorganic
mercury is determined by the flameless atomic absorption spectrophotometric technique using a method similar to that described by Osland et al [8]. Acid stannous
chloride is added to the sample to produce elemental mercury.
Hg
2+
+ Sn
2+
→ Hg
0
+ Sn
4+
The mercury vapour is carried by a stream of air or oxygen into a gas curvette
placed in the path of the radiation from a mercury hollow cathode lamp and the
absorption of this radiation at 253.7 nm by the mercury vapour is measured. Detection
levels in the range 0.1–0.2 µg were achieved by this method. Many of the potential interferences in the atomic absorption procedure are removed by the preliminary
digestion/oxidation procedure. The most significant group of interfering substances is
volatile organic compounds which absorb radiation in the ultraviolet. Most of these
are removed by the pre-treatment procedure used and the effects of any that remain are
overcome by pre-aeration. Bromide and iodide ions may cause interference. Substances
which are reduced to the elemental state by stannous chloride and then form a stable
compound with mercury may cause interference, e.g. selenium, gold, palladium and
platinum. The effects of various anions, including bromide and iodide, were studied.
These are likely to be important interferers.
Farey et al [6] have discussed ultraviolet photochemical systems for the decomposition of organomercury compounds prior to analysis by cold vapour atomic fluorescence
spectroscopy. These workers compared the effectiveness of a bromination treatment for
the liberation of mercury from organomercury compounds and it with a pre-treatment
procedure involving oxidation with a permanganate-sulphuric acid mixture. The basis
of the bromination technique in which a bromate-bromide reagent in hydrochloric acid
is discussed. The main organotin compounds detected in various samples are butylins;
cyclohexyl- and phenyltins were identified in some of the sediment and sewage sludge
samples. Methylbutyltins and tetrabutyltin were not detected. Concentrations were
found to be in a low mg kg
−1 range in sewage sludge.
Miscellaneous
A standard UK procedure discusses the determination of organic, inorganic and total
tin in sludges and sediments [3].
11.3 ORGANOMERCURY COMPOUNDS
Van Ettekoven et al [4] has described a direct semi-automatic scheme based on ultraviolet light absorption for the determination of total mercury in water and sewage sludge.
The full determination is about 10 minutes. The lower limit of detection of mercury
in water is 0.03 µg L
−1 and 0.2 mg L
−1 (mg kg
−1 dry matter) in sewage sludge.
The Department of the Environment (UK) [5] has described a method for determining total organic plus inorganic mercury in non-saline sewage and effluents. All
forms of mercury are converted to inorganic mercury using prolonged oxidation with
potassium permanganage [9]. Solid samples require a more prolonged and vigorous
oxidation to bring the mercury completely into solution in the organic form. A modification of the Uthe digestion procedure is used for such samples [10]. The inorganic
mercury is determined by the flameless atomic absorption spectrophotometric technique using a method similar to that described by Osland et al [8]. Acid stannous
chloride is added to the sample to produce elemental mercury.
Hg
2+
+ Sn
2+
→ Hg
0
+ Sn
4+
The mercury vapour is carried by a stream of air or oxygen into a gas curvette
placed in the path of the radiation from a mercury hollow cathode lamp and the
absorption of this radiation at 253.7 nm by the mercury vapour is measured. Detection
levels in the range 0.1–0.2 µg were achieved by this method. Many of the potential interferences in the atomic absorption procedure are removed by the preliminary
digestion/oxidation procedure. The most significant group of interfering substances is
volatile organic compounds which absorb radiation in the ultraviolet. Most of these
are removed by the pre-treatment procedure used and the effects of any that remain are
overcome by pre-aeration. Bromide and iodide ions may cause interference. Substances
which are reduced to the elemental state by stannous chloride and then form a stable
compound with mercury may cause interference, e.g. selenium, gold, palladium and
platinum. The effects of various anions, including bromide and iodide, were studied.
These are likely to be important interferers.
Farey et al [6] have discussed ultraviolet photochemical systems for the decomposition of organomercury compounds prior to analysis by cold vapour atomic fluorescence
spectroscopy. These workers compared the effectiveness of a bromination treatment for
the liberation of mercury from organomercury compounds and it with a pre-treatment
procedure involving oxidation with a permanganate-sulphuric acid mixture. The basis
of the bromination technique in which a bromate-bromide reagent in hydrochloric acid