9. Pipette 5 ml of each calibration standard and 5 ml of ultrapure
water for blanks to reaction flasks (see Note 4).
10. Add 5 ml oxidizing reagent solution to each flask and close the
flask. Mix by swirling, autoclave for 30 min, and allow to cool
to room temperature.
11. Prepare spectrophotometer or analyzer for analyses according
to the operation manual (see Note 5).
12. Perform manual analyses with a spectrophotometer, or place
standards in the autosampler of an analyzer for a calibration
curve and linearity test (see Note 6).
13. For manual analyses, pipette 0.5 ml of the oxidized standards
and blanks to reaction tubes. Add 3 ml TN mix reagent to each
tube, and close the tubes. Mix well by swirling, incubate for 1 h
at 45
C, and allow to cool to room temperature.
14. Measure the absorbance of blanks and standards with a spectrophotometer in a 1 cm cuvette (or flow-through cuvette) at
545 nm for a calibration curve (see Note 6).
15. Collect the samples in glass bottles or polyethylene bottles, and
analyze the samples immediately after collection. The sample
can be stored in a glass bottle in a refrigerator for a day.
16. Pipette 5 ml of sample (or diluted sample; see Note 7) to
reaction flasks.
17. Add 5 ml oxidizing reagent to each flask and close the flasks.
Add 5 ml oxidizing reagent to three empty flasks for reagent
blanks (see Note 8). Mix by swirling, autoclave for 30 min, and
allow to cool to room temperature.
18. Add 5 ml ultrapure water to the reagent blanks, close the flasks,
and mix well.
19. Perform manual analyses with a spectrophotometer, or place
the samples and reagent blanks in the autosampler of an analyzer. Verify proper operation of the instrument with certified
reference material, and include ultrapure water blanks in the
run (see Note 9).
20. For manual analyses, pipette 0.5 ml of the oxidized samples
and reagent blanks to reaction tubes. Add 3 ml TN mix reagent
to each tube and close the tubes. Mix well by swirling, incubate
1 h at 45
C, and allow to cool to room temperature.
21. Measure the absorbance of the reagent blanks and samples with
a spectrophotometer in a 1 cm cuvette (or flow-through
cuvette) at 545 nm, and calculate the total nitrogen concentration by the calibration curve (see Note 10).
84
Jaana Koistinen et al.
water for blanks to reaction flasks (see Note 4).
10. Add 5 ml oxidizing reagent solution to each flask and close the
flask. Mix by swirling, autoclave for 30 min, and allow to cool
to room temperature.
11. Prepare spectrophotometer or analyzer for analyses according
to the operation manual (see Note 5).
12. Perform manual analyses with a spectrophotometer, or place
standards in the autosampler of an analyzer for a calibration
curve and linearity test (see Note 6).
13. For manual analyses, pipette 0.5 ml of the oxidized standards
and blanks to reaction tubes. Add 3 ml TN mix reagent to each
tube, and close the tubes. Mix well by swirling, incubate for 1 h
at 45
C, and allow to cool to room temperature.
14. Measure the absorbance of blanks and standards with a spectrophotometer in a 1 cm cuvette (or flow-through cuvette) at
545 nm for a calibration curve (see Note 6).
15. Collect the samples in glass bottles or polyethylene bottles, and
analyze the samples immediately after collection. The sample
can be stored in a glass bottle in a refrigerator for a day.
16. Pipette 5 ml of sample (or diluted sample; see Note 7) to
reaction flasks.
17. Add 5 ml oxidizing reagent to each flask and close the flasks.
Add 5 ml oxidizing reagent to three empty flasks for reagent
blanks (see Note 8). Mix by swirling, autoclave for 30 min, and
allow to cool to room temperature.
18. Add 5 ml ultrapure water to the reagent blanks, close the flasks,
and mix well.
19. Perform manual analyses with a spectrophotometer, or place
the samples and reagent blanks in the autosampler of an analyzer. Verify proper operation of the instrument with certified
reference material, and include ultrapure water blanks in the
run (see Note 9).
20. For manual analyses, pipette 0.5 ml of the oxidized samples
and reagent blanks to reaction tubes. Add 3 ml TN mix reagent
to each tube and close the tubes. Mix well by swirling, incubate
1 h at 45
C, and allow to cool to room temperature.
21. Measure the absorbance of the reagent blanks and samples with
a spectrophotometer in a 1 cm cuvette (or flow-through
cuvette) at 545 nm, and calculate the total nitrogen concentration by the calibration curve (see Note 10).
84
Jaana Koistinen et al.