Non-Metals and Sulphides
71
Determination of total phosphorus in lake sediments by ignition of samples in a
muffle furnace at 550°C, boiling of the residue from ignition in 1 mol I-I hydrochloric
acid, and subsequent determination of orthophosphate gave approximately the same
values as the perchloric acid digestion.
Anderson [213] investigated ignition methods for the determination of total phosphorus in lake sediments and biogenic materials, and compared results with those
obtained by perchloric acid digestion. The organic matter is destroyed by ignition.
Material remaining after ignition is boiled in hydrochloric acid and orthophosphate
determined after dilution. The method generally gave lower results than the perchloric acid digestion method (97.7, 98.7, 94.4, 100.5 and 97.3 % for four sediment samples). The reproducibility of the ignition method was slightly less than that observed
with the perchloric acid method.
Perchloric Acid Method [214]. First, 10 ml of demineralized water and 2 ml of concentrated nitric acid were added to 0.15-0.2 g of dry sediment (predried at 103°C) or
plant material in a 100-ml Erlenmeyer flask. After a preliminary oxidation by evaporation of water and nitric acid on a hot plate, 2 ml of concentrated perchloric acid
were added, and the sample was boiled until clear. After cooling, the sample was
diluted to 100 ml and an aliquot was withdrawn for orthophosphate determination by
the ascorbic acid reduction method of Murphy and Riley [214]. Blanks and standards
were treated as samples.
Ignition Method. Dry sediment or plant material (0.15-0.2 g) was ignited in a muffle
furnace in a porcelain crucible (550°C for 1 h). After cooling, the residue was washed
into a 100-ml Erlenmeyer flask with 25 mll mol I-I hydrochloric acid and boiled for
15 min on a hot plate. The sample was diluted to 100 ml and orthophosphate was
determined as in the perchloric acid method. Standards and blanks were not ignited.
The 95 % confidence limits vary from ± 0.5 to ± 1.4 % of the average for the
perchloric acid method and from ± 1.0 to ±2.1 % for the ignition method. Thus, the
reproducibility of the two methods is similar, but a little better for the perchloric acid
method.
Digestion with perchloric acid has been investigated by other workers, as has fusion
with sodium carbonate [215-217].
Aspila et al. [218] have described a simple, rapid, and semi-automated method for
the determination of inorganic, organic and total phosphorus in lake and river
sediments. Total phosphorus is extracted from sediments with 1 mol I-I hydrochloric
acid after ignition at high temperature (550°C) or by digestion with sulphuric acidpotassium persulphate at 135°C in a sealed PTFE-lined Parr bomb. Organic phosphorus is determined by the difference in phosphorus content of the 1 mol I-I hydrochloric acid extract measured before and after ignition of the dry sediments at 550°C.
Orthophosphate is determined by using standard Technicon AutoAnalyzer II techniques. The interferences caused by silica and variable acid concentrations on the
determination of phosphorus were studied.
Freedom from interferences under the chosen experimental conditions as well as
the good results obtained for recovery and precision indicate that the methods are
suitable for monitoring inorganic, organic, and total phosphorus in sediments.
71
Determination of total phosphorus in lake sediments by ignition of samples in a
muffle furnace at 550°C, boiling of the residue from ignition in 1 mol I-I hydrochloric
acid, and subsequent determination of orthophosphate gave approximately the same
values as the perchloric acid digestion.
Anderson [213] investigated ignition methods for the determination of total phosphorus in lake sediments and biogenic materials, and compared results with those
obtained by perchloric acid digestion. The organic matter is destroyed by ignition.
Material remaining after ignition is boiled in hydrochloric acid and orthophosphate
determined after dilution. The method generally gave lower results than the perchloric acid digestion method (97.7, 98.7, 94.4, 100.5 and 97.3 % for four sediment samples). The reproducibility of the ignition method was slightly less than that observed
with the perchloric acid method.
Perchloric Acid Method [214]. First, 10 ml of demineralized water and 2 ml of concentrated nitric acid were added to 0.15-0.2 g of dry sediment (predried at 103°C) or
plant material in a 100-ml Erlenmeyer flask. After a preliminary oxidation by evaporation of water and nitric acid on a hot plate, 2 ml of concentrated perchloric acid
were added, and the sample was boiled until clear. After cooling, the sample was
diluted to 100 ml and an aliquot was withdrawn for orthophosphate determination by
the ascorbic acid reduction method of Murphy and Riley [214]. Blanks and standards
were treated as samples.
Ignition Method. Dry sediment or plant material (0.15-0.2 g) was ignited in a muffle
furnace in a porcelain crucible (550°C for 1 h). After cooling, the residue was washed
into a 100-ml Erlenmeyer flask with 25 mll mol I-I hydrochloric acid and boiled for
15 min on a hot plate. The sample was diluted to 100 ml and orthophosphate was
determined as in the perchloric acid method. Standards and blanks were not ignited.
The 95 % confidence limits vary from ± 0.5 to ± 1.4 % of the average for the
perchloric acid method and from ± 1.0 to ±2.1 % for the ignition method. Thus, the
reproducibility of the two methods is similar, but a little better for the perchloric acid
method.
Digestion with perchloric acid has been investigated by other workers, as has fusion
with sodium carbonate [215-217].
Aspila et al. [218] have described a simple, rapid, and semi-automated method for
the determination of inorganic, organic and total phosphorus in lake and river
sediments. Total phosphorus is extracted from sediments with 1 mol I-I hydrochloric
acid after ignition at high temperature (550°C) or by digestion with sulphuric acidpotassium persulphate at 135°C in a sealed PTFE-lined Parr bomb. Organic phosphorus is determined by the difference in phosphorus content of the 1 mol I-I hydrochloric acid extract measured before and after ignition of the dry sediments at 550°C.
Orthophosphate is determined by using standard Technicon AutoAnalyzer II techniques. The interferences caused by silica and variable acid concentrations on the
determination of phosphorus were studied.
Freedom from interferences under the chosen experimental conditions as well as
the good results obtained for recovery and precision indicate that the methods are
suitable for monitoring inorganic, organic, and total phosphorus in sediments.