Nitrate
Nitrate
Page 4 of 6
Nitrate_AVPP_HR_CDR_Eng_Ody.fm
Interferences
Sample Collection, Storage, and Preservation
More reliable results are obtained when samples are analyzed as soon as possible
after collection. If prompt analysis is impossible, store samples in clean plastic or
glass bottles for up to 24 hours at 4 °C. To preserve samples for longer periods,
add 2 mL of Concentrated Sulfuric Acid (H
2
SO
4
) (Cat. No. 979-49) per liter and
store at 4 °C.
Before analysis, warm the sample to room temperature and adjust the pH to 7
with 5.0 N Sodium Hydroxide Standard Solution (Cat. No. 2450-53). Do not use
mercury compounds as preservatives. Correct the test result for volume
additions by dividing the total volume (acid + base + sample) by the original
sample volume and multiplying the test result by this factor.
9. Within one minute
after the timer beeps,
wipe the ampule and
place into the cell holder.
10. Touch Read.
Results will appear in
mg/L NO
3
–
–N.
Interfering Substance Interference Levels and Treatments
Chloride
Chloride concentrations above 100 mg/L will cause low results. The test may be used at high
chloride concentrations (seawater) but a calibration must be done using standards spiked to the
same chloride concentration.
Ferric iron Interferes at all levels
Nitrite
Interferes at all levels
Compensate for nitrite interference as follows:
a) Before performing step 3, add 30-g/L Bromine Water (Cat. No. 2211-20) dropwise to the
sample until a yellow color remains.
b) Add one drop of 30-g/L Phenol Solution (Cat. No. 2112-20) to destroy the color.
Proceed with step 3. Report the results as total nitrate and nitrite.
pH
Highly buffered samples or extreme sample pH may exceed the buffering capacity of the
reagents and require sample pretreatment.
Strong oxidizing and
reducing substances
Interfere at all levels
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