final total volume of 100 ml. Store in a glass bottle in a refrigerator (stable about 1 month).
6. On the day of analyses, prepare working solutions of nitrate
(0–100 μg/l) for calibration by diluting the standard stock
solution (see Step 5) with ultrapure water (e.g., 1 ml to
100 ml for 1400 μg/l solution and then, e.g., 7.143 ml of
this dilution to 100 ml ultrapure water for 100 μg/l solution).
7. Prepare analyzer for analyses according to the operation manual (see Note 1).
8. 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).
9. For manual analyses, pipette three, e.g., 2 ml portions of each
working standard and three 2 ml aliquots of ultrapure water as
blanks to reaction flasks and add 2 ml mix reagent to standards
and blanks. Close the flasks, mix well by swirling, and incubate
for 1 h at 45
C. Measure the absorbance of blanks and standards with a spectrophotometer in a 1 cm cuvette at 540 nm
(see Note 2).
10. Collect the samples in glass bottles or polyethylene bottles and
analyze the samples immediately after collection (within 1 h).
The sample can be stored in a glass bottle in a refrigerator for
about 5 h.
11. 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).
12. For manual analyses, pipette 2 ml aliquot of each sample with a
pipette to a reaction flask, add 2 ml mix reagent to the flask,
close, mix well by swirling, and incubate 1 h at 45
C. Measure
the absorbance of the sample in a 1 cm cuvette at 540 nm
and calculate the nitrate concentration by the calibration curve
(see Notes 4 and 5).
3.2 Ammonium
Perform analyses in a well-ventilated room where no ammoniacal
solutions are stored. The procedure follows that of Koroleff in the
first edition of [1] and [4].
1. Prepare 0.5 mol/l sodium hydroxide solution by dissolving
20 g sodium hydroxide in ultrapure water, and then add ultrapure water to a final total volume of 1000 ml. Store in a
polyethylene bottle.
2. Prepare reagent II (Phenol solution) by dissolving 38 g phenol
and 400 mg disodium nitroprusside dihydrate in ultrapure
water (protect from light by wrapping the bottle in aluminum
foil) and add ultrapure water to a final volume of 1000 ml.
Determining Inorganic and Organic Nitrogen
75
6. On the day of analyses, prepare working solutions of nitrate
(0–100 μg/l) for calibration by diluting the standard stock
solution (see Step 5) with ultrapure water (e.g., 1 ml to
100 ml for 1400 μg/l solution and then, e.g., 7.143 ml of
this dilution to 100 ml ultrapure water for 100 μg/l solution).
7. Prepare analyzer for analyses according to the operation manual (see Note 1).
8. 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).
9. For manual analyses, pipette three, e.g., 2 ml portions of each
working standard and three 2 ml aliquots of ultrapure water as
blanks to reaction flasks and add 2 ml mix reagent to standards
and blanks. Close the flasks, mix well by swirling, and incubate
for 1 h at 45
C. Measure the absorbance of blanks and standards with a spectrophotometer in a 1 cm cuvette at 540 nm
(see Note 2).
10. Collect the samples in glass bottles or polyethylene bottles and
analyze the samples immediately after collection (within 1 h).
The sample can be stored in a glass bottle in a refrigerator for
about 5 h.
11. 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).
12. For manual analyses, pipette 2 ml aliquot of each sample with a
pipette to a reaction flask, add 2 ml mix reagent to the flask,
close, mix well by swirling, and incubate 1 h at 45
C. Measure
the absorbance of the sample in a 1 cm cuvette at 540 nm
and calculate the nitrate concentration by the calibration curve
(see Notes 4 and 5).
3.2 Ammonium
Perform analyses in a well-ventilated room where no ammoniacal
solutions are stored. The procedure follows that of Koroleff in the
first edition of [1] and [4].
1. Prepare 0.5 mol/l sodium hydroxide solution by dissolving
20 g sodium hydroxide in ultrapure water, and then add ultrapure water to a final total volume of 1000 ml. Store in a
polyethylene bottle.
2. Prepare reagent II (Phenol solution) by dissolving 38 g phenol
and 400 mg disodium nitroprusside dihydrate in ultrapure
water (protect from light by wrapping the bottle in aluminum
foil) and add ultrapure water to a final volume of 1000 ml.
Determining Inorganic and Organic Nitrogen
75