Hach DR2400 - Page 483

Nitrogen, Ammonia
Nitrogen, Ammonia
NitrogenAmm_TNT_Low_SAL_Eng_Ody.fm Page 3 of 6
Sample Collection, Storage, and Preservation
Collect samples in clean plastic or glass bottles. Best results are obtained with
immediate analysis. If chlorine is known to be present, add one drop of
0.1 N Sodium Thiosulfate (Cat. No. 323-32) for each 0.3 mg/L Cl
2
in a one liter
sample. Preserve the sample by reducing the pH to 2 or less with at least 2 mL of
Hydrochloric Acid (Cat. No. 134-49). Store at 4 °C (39 °F) or less. Preserved
samples may be stored up to 28 days. Before analysis, warm samples to room
temperature and neutralize to pH 7.0 with 5.0 N Sodium Hydroxide (Cat. No.
2450-26). 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 an Ammonia Nitrogen Ampule Standard,
50-mg/L as 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 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.
pH
Acidic or basic samples should be adjusted to approximately pH 7. Use 1 N Sodium Hydroxide
Standard Solution (Cat. No. 1045-32) for acidic samples and 1 N Hydrochloric Acid Standard
Solution (Cat. No. 23213-53) for basic samples.
Sulfate 300 mg/L as SO
4
2–
Sulfide
1. Measure about 350 mL of sample in a 500-mL Erlenmeyer flask.
2. Add the contents of one Sulfide Inhibitor Reagent Powder Pillow (Cat. No. 2418-99).
Swirl to mix.
3. Filter the sample through a Folded Filter Paper (Cat. No. 1894-57) in a Filter Funnel
(Cat. No. 1083-67).
4. Use the filtered solution in step 3.
Other
Less common interferences such as hydrazine and glycine will cause intensified colors in the
prepared sample. Turbidity and color will give erroneous high values. Samples with severe
interferences require distillation. Hach recommends the distillation procedure using the Hach
General Purpose Distillation Set (Cat. No. 22653-00).
(continued)
Interfering Substance Interference Levels and Treatments