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Exercise 7
4. Sulfanilamide solution: Dissolve 5 g of sulfanilamide in a solution of 50 ml of
concentrated HCI (sp. gr. 1.18) and 300 ml of distilled water. Dilute with water to
500ml.
5. N-(1-naphthyl) ethylene diamine dihydrochloride solution: Dissolve 0.5 g of dihydrochloride in 500 ml distilled water. Store in amber or low actinic glass bottle;
renew once a month or earlier if dark brown coloration develops.
6. Nitrate standard: Dissolve 0.722 g ofKN0 3 (dried for 1 h at 110°C) in distilled water
and make to 1 liter:
1.00ml = 100,ug N0 3 -N.
7. Nitrite standard: Dissolve 0.4929 g of NaN0 2 (dried for 1 h at 110°C) in distilled
water and make to 1 liter:
1.00ml = 100,ugN0 2 -N
Procedures for Nitrate Nitrogen
1. Prepare duplicate aliquots of nitrate standard to yield 50 ml from each Cd-Cu
reduction column. The concentrations used should approximate those of the
samples to be analyzed and include concentrations both lower and higher than
those of the samples.
2. Place 50 ml of distilled water (blank), nitrate standards, and samples into
graduated cylinders. Add 5 ml of buffer solution and mix thoroughly (with
stoppered cylinders, invert; if baseless cylinders are used, a vortex mixer is very
effective and rapid).
3. Add 10 ml of the buffered sample to the column, allow it to run through, and
discard the effiuent.
4. Add the remainder of the buffered solution to the column, collect 2 ml of effiuent in
the same cylinder, rinse the walls ofthe cylinder, discard the effiuent, and shake the
cylinder as dryas possible. Collect exactly 25 ml of the column effiuent. A distilled
water blank and a standard solution must be carried through each column used.
5. As soon as possible, and 0.5 ml of the sulfanilamide solution to the 25-ml sample of
effiuent from the column and mix well.
6. After 5 min, but not exceeding 8 min, add 0.5 ml of the naphthyl ethylenediamine
solution and mix immediately.
7. Between 10 min and 2 h later, measure the extinction coefficient at a wavelength of
543 nm ofthe solution in a 1-cm (or longer) cell. Use distilled water as a reference.
When the extinction coefficient is greater than about 1.2, dilute by exactly one-half
with distilled water and remeasure. Remember to double the value obtained from
the one-half-strength solution. Path lengths of 1 cm, 5 cm, and 10 cm are
appropriate for nitrate concentrations of about 60 to 300, 30 to 60, and 0 to 30,ug
N0 3 -N/l, respectively.
If the samples of water have a visible natural coloration, a sample blank without
the addition of naphthyl ethylenediamine reagent should be processed.
The following extinction values then are obtained:
OD b = absorbance of distilled water plus reagents; the "blank"
00 0 = absorbance of samples without naphthyl ethylenediamine reagent (if
brown coloration exists)
ODs = absorbance of standards or samples plus reagents
8. Intersperse water samples, standards, and blanks. At least three standard solutions
should be used and the range of the samples should be bracketed.
Exercise 7
4. Sulfanilamide solution: Dissolve 5 g of sulfanilamide in a solution of 50 ml of
concentrated HCI (sp. gr. 1.18) and 300 ml of distilled water. Dilute with water to
500ml.
5. N-(1-naphthyl) ethylene diamine dihydrochloride solution: Dissolve 0.5 g of dihydrochloride in 500 ml distilled water. Store in amber or low actinic glass bottle;
renew once a month or earlier if dark brown coloration develops.
6. Nitrate standard: Dissolve 0.722 g ofKN0 3 (dried for 1 h at 110°C) in distilled water
and make to 1 liter:
1.00ml = 100,ug N0 3 -N.
7. Nitrite standard: Dissolve 0.4929 g of NaN0 2 (dried for 1 h at 110°C) in distilled
water and make to 1 liter:
1.00ml = 100,ugN0 2 -N
Procedures for Nitrate Nitrogen
1. Prepare duplicate aliquots of nitrate standard to yield 50 ml from each Cd-Cu
reduction column. The concentrations used should approximate those of the
samples to be analyzed and include concentrations both lower and higher than
those of the samples.
2. Place 50 ml of distilled water (blank), nitrate standards, and samples into
graduated cylinders. Add 5 ml of buffer solution and mix thoroughly (with
stoppered cylinders, invert; if baseless cylinders are used, a vortex mixer is very
effective and rapid).
3. Add 10 ml of the buffered sample to the column, allow it to run through, and
discard the effiuent.
4. Add the remainder of the buffered solution to the column, collect 2 ml of effiuent in
the same cylinder, rinse the walls ofthe cylinder, discard the effiuent, and shake the
cylinder as dryas possible. Collect exactly 25 ml of the column effiuent. A distilled
water blank and a standard solution must be carried through each column used.
5. As soon as possible, and 0.5 ml of the sulfanilamide solution to the 25-ml sample of
effiuent from the column and mix well.
6. After 5 min, but not exceeding 8 min, add 0.5 ml of the naphthyl ethylenediamine
solution and mix immediately.
7. Between 10 min and 2 h later, measure the extinction coefficient at a wavelength of
543 nm ofthe solution in a 1-cm (or longer) cell. Use distilled water as a reference.
When the extinction coefficient is greater than about 1.2, dilute by exactly one-half
with distilled water and remeasure. Remember to double the value obtained from
the one-half-strength solution. Path lengths of 1 cm, 5 cm, and 10 cm are
appropriate for nitrate concentrations of about 60 to 300, 30 to 60, and 0 to 30,ug
N0 3 -N/l, respectively.
If the samples of water have a visible natural coloration, a sample blank without
the addition of naphthyl ethylenediamine reagent should be processed.
The following extinction values then are obtained:
OD b = absorbance of distilled water plus reagents; the "blank"
00 0 = absorbance of samples without naphthyl ethylenediamine reagent (if
brown coloration exists)
ODs = absorbance of standards or samples plus reagents
8. Intersperse water samples, standards, and blanks. At least three standard solutions
should be used and the range of the samples should be bracketed.