Hach DR2400 - Page 493

Nitrogen, Ammonium
Nitrogen, Ammonium
NitrogenAmm_UniCell_Low_SAL_Eng_Ody.fm Page 3 of 4
Sample, Collection, Storage, and Preservation
Analyze samples within 3 hours after collection for best results. Collect samples
in clean plastic or glass bottles. To preserve samples for longer periods, add 1 mL
of concentrated sulfuric acid per liter and store at 4 °C.
Warm the sample to room temperature before testing. Adjust the pH to 4–9 with
5.0 N sodium hydroxide. Do not use mercury compounds as preservatives.
Correct the test results for volume additions by dividing the total final volume
(acid + base + sample) by the initial sample volume and multiplying the result
by this factor. 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. Enter 128.6 mg/L NH
4
+
(100-mg/L NH
3
–N) as the standard concentration.
4. Touch
OK to accept the default values for 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.
5. Prepare three sample spikes. Fill three 100-mL Mixing Cylinders
(Cat. No. 20886-42) with 100 mL of sample. Use a pipet to add 0.2 mL, 0.4 mL,
and 0.6 mL of (128.6 mg/L NH
4
+
) 100-mg/L NH
3
–N standard, respectively,
to each sample and mix thoroughly.
6. Analyze each sample spike as described in the procedure above, starting with
the 0.2 mL sample spike. Accept each standard additions reading by touching
Read. Each addition should reflect approximately 100% recovery.
7. After completing the sequence, touch
Graph to view the best-fit line through
the standard additions data points, accounting for matrix interferences. Touch
View: Fit, then select Ideal Line and touch OK to view the relationship between
the sample spikes and the “Ideal Line” of 100% recovery.
See Section 3.2.2 Standard Additions on page 32 for more information.
Standard Solution Method
To check accuracy, use the Nitrogen Ammonia Standard Solution, 1.0-mg/L.
Alternatively, dilute 1 mL of 50-mg/L Nitrogen Ammonia Standard Solution to
50 mL with deionized water in a 50-mL volumetric flask.
Note: Make sure that the selected chemical form is NH
4
+
–N.