Nitrogen, Ammonia
Nitrogen, Ammonia
NitrogenAmm_None_Other_NES_Eng_Ody.fm Page 3 of 6
Interferences
Sample Collection, Storage, and Preservation
Collect samples in clean glass or plastic bottles. If chlorine is present, add one
drop of 0.1 N Sodium Thiosulfate (Cat. No. 323-32) for each 0.3 mg/L Cl
2
in a
1-liter sample. Preserve the sample by reducing the pH to 2 or less with sulfuric
acid (at least 2 mL). Store at 4 °C (39 °F) or less. Preserved samples may be stored
up to 28 days. Warm samples to room temperature and neutralize with 5 N
Sodium Hydroxide (Cat. No. 2450-32) before analysis. Correct the test result for
volume additions; see Section 3.1.3 Correcting for Volume Additions on page 29.
Accuracy Check
Standard Additions Method (Sample Spike)
1. After reading test results, leave the sample cell (unspiked sample) in the
instrument.
2. Touch
Options. Touch Standard Additions. A summary of the standard
additions procedure will appear.
3. Touch
OK to accept the default values for standard concentration, sample
volume, and spike volumes. Touch
Edit to change these values. After values
are accepted, the unspiked sample reading will appear in the top row. See
Standard Additions in the instrument manual for more information.
4. Snap the neck off a Nitrogen Ammonia Voluette
®
Ampule Standard,
50-mg/L NH
3
–N.
5. Prepare three sample spikes. Fill three mixing cylinders (Cat. No. 1896-40)
with 25 mL of sample. Use the TenSette
®
Pipet to add 0.1 mL, 0.2 mL,
and 0.3 mL of the 50 mg/L standard, respectively, to each sample and mix
thoroughly.
6. Analyze each sample spike as described in the procedure above, starting with
the 0.1 mL sample spike. Accept each standard additions reading by touching
Read. Each addition should reflect approximately 100% recovery.
Interfering Substance Interference Levels and Treatments
Chlorine
Remove residual chlorine by adding 2 drops of sodium arsenite for each mg/L Cl from a 250 mL
sample. Sodium thiosulfate can be used in place of sodium arsenite. See Sample Collection,
Storage, and Preservation below.
Hardness
A solution containing a mixture of 500 mg/L CaCO
3
and 500 mg/L Mg as CaCO
3
does not
interfere. If the hardness concentration exceeds these concentrations, add extra
Mineral Stabilizer.
Iron Interferes at all levels by causing turbidity with Nessler Reagent.
Seawater
May be analyzed by adding of 1.0 mL (27 drops) of Mineral Stabilizer to the sample before
analysis. This complexes the high magnesium concentrations found in sea water, but the
sensitivity of the test is reduced by 30 percent due to the high chloride concentration. For best
results, perform a calibration, using standards spiked to the equivalent chloride concentration, or
distill the sample as described below.
Sulfide Interferes at all levels by causing turbidity with Nessler Reagent.
Glycine, various aliphatic and
aromatic amines, organic
chloramines, acetone,
aldehydes and alcohols
May cause greenish or other off colors or turbidity. Distill the sample if these compounds
are present.
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