50
River and Stream Sediments
2.2
Non-Metals
2.2.1
Total Nitrogen
Potassium persulphate [75], hydrogen peroxide [76], and peroxy-disulphate in alkaline medium [77] have all been used to digest river sediments prior to the determination of total nitrogen. Muhlhauser et al. [76] digested 10 mg sediment with 25 ml
water, 0.2 ml concentrated sulphuric acid and 0.4 ml hydrogen peroxide for 4.5 h at
250°C.
Zink-Nielsen [77] showed that higher total nitrogen contents with lower coefficient
of variation deviations (7.88 ± CV 3.8 mg N g-l dry weight) are obtained when river
sediments are digested under reducing Kjeldahl conditions (salicylic acid and sodium
thiosulphate) than when digestion was carried out using alkaline potassium peroxydisulphate, (6.46 ± CV 8.4 mg N g-l dry weight) indicating that peroxydisulphate is not
a strong enough oxidising agent to convert all organic nitrogen to nitrate nitrogen.
2.2.2
Organic and Total Phosphorus
Olsen et al. [78] have reviewed the determination of inorganic, organic and total
phosphorus in water, soil, and sediments. Determination of total phosphorus in
aqueous samples commonly involves a hot acid oxidation type digestion procedure,
although various other dry-ashing, fusion, and UV irradiation methods have been
reported and evaluated, e. g. Harwood et al. [79], and Osburn et al. [80] Zink-Nielsen
[77] obtained 0.9 ± 5.7 mg P g-l dry weight total phosphorus in a river sediment
following digestion with potassium peroxydisulphate and a higher result with a lower
standard deviation (0.98 ± 3.4 mg P g-l dry weight) by Kjeldahl digestion followed by
spectrophotometric estimation by the molybdate-ascorbic acid method.
Aspila et al. [81] have described a semi-automated method for the determination of
inorganic, organic and total phosphorus in river and lake sediments. Total phosphorus is extracted from sediments with 1 N hydrochloric acid after ignition at a high
temperature (550 0c) (method 1) or by digestion with sulphuric acid-potassium persulphate at 135 °c in a sealed PTFE-lined Parr bomb (Method 2).
Organic phosphorus is determined by the difference in phosphorus content of the
1 N hydrochloric acid extract measured before and after ignition of the dry sediments
at 550 °c. In all instances the orthophosphate is determined by using standard Technicon AutoAnalyzer II techniques. Silica does not interfere.
River and Stream Sediments
2.2
Non-Metals
2.2.1
Total Nitrogen
Potassium persulphate [75], hydrogen peroxide [76], and peroxy-disulphate in alkaline medium [77] have all been used to digest river sediments prior to the determination of total nitrogen. Muhlhauser et al. [76] digested 10 mg sediment with 25 ml
water, 0.2 ml concentrated sulphuric acid and 0.4 ml hydrogen peroxide for 4.5 h at
250°C.
Zink-Nielsen [77] showed that higher total nitrogen contents with lower coefficient
of variation deviations (7.88 ± CV 3.8 mg N g-l dry weight) are obtained when river
sediments are digested under reducing Kjeldahl conditions (salicylic acid and sodium
thiosulphate) than when digestion was carried out using alkaline potassium peroxydisulphate, (6.46 ± CV 8.4 mg N g-l dry weight) indicating that peroxydisulphate is not
a strong enough oxidising agent to convert all organic nitrogen to nitrate nitrogen.
2.2.2
Organic and Total Phosphorus
Olsen et al. [78] have reviewed the determination of inorganic, organic and total
phosphorus in water, soil, and sediments. Determination of total phosphorus in
aqueous samples commonly involves a hot acid oxidation type digestion procedure,
although various other dry-ashing, fusion, and UV irradiation methods have been
reported and evaluated, e. g. Harwood et al. [79], and Osburn et al. [80] Zink-Nielsen
[77] obtained 0.9 ± 5.7 mg P g-l dry weight total phosphorus in a river sediment
following digestion with potassium peroxydisulphate and a higher result with a lower
standard deviation (0.98 ± 3.4 mg P g-l dry weight) by Kjeldahl digestion followed by
spectrophotometric estimation by the molybdate-ascorbic acid method.
Aspila et al. [81] have described a semi-automated method for the determination of
inorganic, organic and total phosphorus in river and lake sediments. Total phosphorus is extracted from sediments with 1 N hydrochloric acid after ignition at a high
temperature (550 0c) (method 1) or by digestion with sulphuric acid-potassium persulphate at 135 °c in a sealed PTFE-lined Parr bomb (Method 2).
Organic phosphorus is determined by the difference in phosphorus content of the
1 N hydrochloric acid extract measured before and after ignition of the dry sediments
at 550 °c. In all instances the orthophosphate is determined by using standard Technicon AutoAnalyzer II techniques. Silica does not interfere.