3.2 Dissolved
Organic Phosphorus
from Total Phosphorus
Measurements
The procedure follows that of Koroleff [4].
1. Prepare 4.5 mol/l sulfuric acid solution (see Sect. 3.1).
2. Prepare oxidizing reagent by diluting 15 ml of 4.5 mol/l
sulfuric acid to 100 ml with ultrapure water. Dissolve 5 g
potassium peroxodisulfate in the solution. Store in a polyethylene bottle protected from light at room temperature (stable for
about 1 week).
3. Prepare molybdate solution (see Sect. 3.1).
4. Prepare tartrate solution (see Sect. 3.1).
5. Prepare reagent I (ascorbic acid solution) by dissolving 7.0 g
ascorbic acid in 100 ml ultrapure water. Store in an amber glass
bottle in a refrigerator (stable for at least 1 month, usable as
long as almost colorless).
6. Prepare reagent II (mix reagent) (see Sect. 3.1).
7. Prepare phosphate standard 310 μg P/ml (see Sect. 3.1).
8. On the day of analysis, prepare suitable working solutions of
phosphate (0–600 μg P/l) for calibration by diluting the standard stock solution (see Sect. 3.1) with ultrapure water (e.g.,
0.2 ml in 100 ml ultrapure water for 620 μg P/l solution).
9. Measure 35 ml of each calibration standard and 35 ml of ultrapure water for blanks with graduated cylinder to reaction flasks.
10. Add 2 ml oxidizing reagent solution to the flasks and dissolve
by swirling. Close the flasks and place in the autoclave. Autoclave for 30 min and allow to cool to room temperature.
11. Prepare analyzer for analyses according to the operation manual (see Note 1). Dilute the reagents 1:10 for analyzer.
12. Place standards in the autosampler of an analyzer, or measure
the standards manually by a spectrophotometer for a calibration curve and linearity test (see Note 2).
13. For manual analyses, add 1 ml of reagent I (see step 5) to
standards and blanks. Mix well by swirling.
14. Add 1 ml of reagent II (see step 6) to standards and blanks. Mix
well by swirling and allow to react for 10 min.
15. Measure the absorbance of blanks and standards in a 5 cm
cuvette at 880 nm for a calibration curve (see Note 2).
16. Filter the sample with the syringe and syringe filter. Rinse the
syringe with the sample before filtering. Prepare filter blank by
filtering ultrapure water.
17. Collect the samples in polyethylene bottles and analyze the samples immediately after collection (within 2 h).
18. Measure 35 ml of the sample with a graduated cylinder to
reaction flasks.
Determining Phosphorus Concentration
91
Organic Phosphorus
from Total Phosphorus
Measurements
The procedure follows that of Koroleff [4].
1. Prepare 4.5 mol/l sulfuric acid solution (see Sect. 3.1).
2. Prepare oxidizing reagent by diluting 15 ml of 4.5 mol/l
sulfuric acid to 100 ml with ultrapure water. Dissolve 5 g
potassium peroxodisulfate in the solution. Store in a polyethylene bottle protected from light at room temperature (stable for
about 1 week).
3. Prepare molybdate solution (see Sect. 3.1).
4. Prepare tartrate solution (see Sect. 3.1).
5. Prepare reagent I (ascorbic acid solution) by dissolving 7.0 g
ascorbic acid in 100 ml ultrapure water. Store in an amber glass
bottle in a refrigerator (stable for at least 1 month, usable as
long as almost colorless).
6. Prepare reagent II (mix reagent) (see Sect. 3.1).
7. Prepare phosphate standard 310 μg P/ml (see Sect. 3.1).
8. On the day of analysis, prepare suitable working solutions of
phosphate (0–600 μg P/l) for calibration by diluting the standard stock solution (see Sect. 3.1) with ultrapure water (e.g.,
0.2 ml in 100 ml ultrapure water for 620 μg P/l solution).
9. Measure 35 ml of each calibration standard and 35 ml of ultrapure water for blanks with graduated cylinder to reaction flasks.
10. Add 2 ml oxidizing reagent solution to the flasks and dissolve
by swirling. Close the flasks and place in the autoclave. Autoclave for 30 min and allow to cool to room temperature.
11. Prepare analyzer for analyses according to the operation manual (see Note 1). Dilute the reagents 1:10 for analyzer.
12. Place standards in the autosampler of an analyzer, or measure
the standards manually by a spectrophotometer for a calibration curve and linearity test (see Note 2).
13. For manual analyses, add 1 ml of reagent I (see step 5) to
standards and blanks. Mix well by swirling.
14. Add 1 ml of reagent II (see step 6) to standards and blanks. Mix
well by swirling and allow to react for 10 min.
15. Measure the absorbance of blanks and standards in a 5 cm
cuvette at 880 nm for a calibration curve (see Note 2).
16. Filter the sample with the syringe and syringe filter. Rinse the
syringe with the sample before filtering. Prepare filter blank by
filtering ultrapure water.
17. Collect the samples in polyethylene bottles and analyze the samples immediately after collection (within 2 h).
18. Measure 35 ml of the sample with a graduated cylinder to
reaction flasks.
Determining Phosphorus Concentration
91