Nitrate
Nitrate
Nitrate_PP_Low_CDR_Eng_Ody.fm Page 3 of 6
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 48 hours at 4 °C. To preserve samples for longer periods,
add 2 mL of Concentrated Sulfuric Acid (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.
13. Place the prepared
sample into the cell
holder.
14. Touch Read.
Results will appear in
mg/L NO
3
–
–N.
Interfering Substance Interference Levels and Treatments
Calcium 100 mg/L
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 All levels
Nitrite
All levels: This method measures both the nitrate and nitrite in the sample. If nitrite is present,
the nitrite nitrogen test (Program #371) should be done on the sample. Pretreat the nitrate
nitrogen sample with the following pretreatment. Then subtract the amount of nitrite found from
the results of the LR nitrate nitrogen test.
1. Add 30-g/L Bromine Water (Cat. No. 2211-20) dropwise to the sample in step 3 until a yellow
color remains. Mix after each drop.
2. Add one drop of 30-g/L Phenol Solution (Cat. No. 2112-20) to destroy the color.
3. Proceed with the LR Nitrate procedure.
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
10 mL
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