13. Prepare POP reagent II (mix reagent; as in Sect. 3.1 reagent II,
except 100 ml 4.5 mol/l H 2 SO 4 and no water).
14. Prepare phosphate standard 310 μg P/ml (see Sect. 3.1).
15. Prepare 0.2 mol/l HCl solution. Carefully add 16.6 ml concentrated HCl to 500 ml of ultrapure water, cool, and make up
to 1000 ml with ultrapure water. Store in a glass bottle at room
temperature (stable for months).
16. Prepare working standards of phosphate (0–600 μg P/l) for
calibration by diluting the standard stock solution with ultrapure water (e.g., 0.2 ml in 100 ml for 620 μg P/l solution).
17. Pipette 10 ml calibration solution and 10 ml ultrapure water
for blanks to scintillation vials, and add 200 μl of 0.17 mol/l
MgSO 4 .
18. Standards and blanks are put in warm cabinet at 95
C until
solution has dried completely.
19. Put in oven at 450
C for 2 h.
20. Add 5 ml 0.2 mol/l HCl and add lids.
21. Place in water bath, 80
C for 30 min, and cool to room temperature.
22. Add 5 ml ultrapure water, and leave for 10 min.
23. Prepare analyzer for analyses according to the operation manual (see Note 1). Dilute the reagents 1:10 for analyzer.
24. 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).
25. For manual analyses, add 300 μl of POP reagent I and mix by
swirling. Add 300 μl POP reagent II. Mix well by swirling and
allow to react for 10 min.
26. Measure the absorbance of standards and blanks in a 2 cm cuvette
at 880 nm for a calibration curve and linearity test (see Note 2).
27. When measuring samples, start by adding 2 ml 0.017 mol/l
MgSO 4 . Prepare 0.017 mol/l MgSO4 solution by diluting
0.17 mol/l solution with ultrapure water.
28. Put in warm cabinet at 95
C until solution has dried.
29. Put in oven at 450
C for 2 h (see Note 8).
30. Add 5 ml 0.2 mol/l HCl and add lids.
31. Place in water bath, 80
C for 30 min, and cool to room temperature.
32. Add 5 ml ultrapure water.
33. Place samples in the autosampler of an analyzer, or perform
manual analyses with a spectrophotometer. Verify proper operation of the instrument with certified reference material, and
include ultrapure water blanks in the run (see Note 3).
34. For manual analyses, add 300 μl POP reagent I and mix by
swirling. Add 300 μl POP reagent II mix well by swirling, and
allow to react for 10 min.
Determining Phosphorus Concentration
93
except 100 ml 4.5 mol/l H 2 SO 4 and no water).
14. Prepare phosphate standard 310 μg P/ml (see Sect. 3.1).
15. Prepare 0.2 mol/l HCl solution. Carefully add 16.6 ml concentrated HCl to 500 ml of ultrapure water, cool, and make up
to 1000 ml with ultrapure water. Store in a glass bottle at room
temperature (stable for months).
16. Prepare working standards of phosphate (0–600 μg P/l) for
calibration by diluting the standard stock solution with ultrapure water (e.g., 0.2 ml in 100 ml for 620 μg P/l solution).
17. Pipette 10 ml calibration solution and 10 ml ultrapure water
for blanks to scintillation vials, and add 200 μl of 0.17 mol/l
MgSO 4 .
18. Standards and blanks are put in warm cabinet at 95
C until
solution has dried completely.
19. Put in oven at 450
C for 2 h.
20. Add 5 ml 0.2 mol/l HCl and add lids.
21. Place in water bath, 80
C for 30 min, and cool to room temperature.
22. Add 5 ml ultrapure water, and leave for 10 min.
23. Prepare analyzer for analyses according to the operation manual (see Note 1). Dilute the reagents 1:10 for analyzer.
24. 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).
25. For manual analyses, add 300 μl of POP reagent I and mix by
swirling. Add 300 μl POP reagent II. Mix well by swirling and
allow to react for 10 min.
26. Measure the absorbance of standards and blanks in a 2 cm cuvette
at 880 nm for a calibration curve and linearity test (see Note 2).
27. When measuring samples, start by adding 2 ml 0.017 mol/l
MgSO 4 . Prepare 0.017 mol/l MgSO4 solution by diluting
0.17 mol/l solution with ultrapure water.
28. Put in warm cabinet at 95
C until solution has dried.
29. Put in oven at 450
C for 2 h (see Note 8).
30. Add 5 ml 0.2 mol/l HCl and add lids.
31. Place in water bath, 80
C for 30 min, and cool to room temperature.
32. Add 5 ml ultrapure water.
33. Place samples in the autosampler of an analyzer, or perform
manual analyses with a spectrophotometer. Verify proper operation of the instrument with certified reference material, and
include ultrapure water blanks in the run (see Note 3).
34. For manual analyses, add 300 μl POP reagent I and mix by
swirling. Add 300 μl POP reagent II mix well by swirling, and
allow to react for 10 min.
Determining Phosphorus Concentration
93