Hach DR2400 - Page 441

Nitrate
Nitrate
Nitrate_TNT_High_CHA_Eng_Ody.fm Page 3 of 4
Sample Collection, Preservation, and Storage
Collect samples in clean plastic or glass bottles. Store at 4 °C (39 °F) or lower if
the sample is to be analyzed within 24 to 48 hours. Warm to room temperature
before running the test. For longer storage periods (up to 14 days), adjust sample
pH to 2 or less with Concentrated Sulfuric Acid, ACS (about 2 mL per liter)
(Cat. No. 979-49). Sample refrigeration is still required.
Before testing the stored sample, warm to room temperature and neutralize with
5.0 N Sodium Hydroxide Standard Solution (Cat. No. 2450-26).
Do not use mercury compounds as preservatives.
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. Verify the chemical form.
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 High Range Nitrate Nitrogen Voluette
®
Ampule Standard,
500 mg/L NO
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.
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
Use a 10.0-mg/L Nitrate Nitrogen Standard Solution to check test accuracy.
See Section 3.2.1 Standard Solutions on page 31 for more information.