Hach DR2400 - Page 445

Nitrate
Nitrate
Nitrate_UniCell_Dimeth_Eng_Ody.fm Page 3 of 4
Sample Collection, Preservation, and Storage
Analyze samples within three hours after collection for best results. Collect
samples in clean plastic or glass bottles. Store in a cool place. Warm to room
temperature before performing the test. For longer storage periods, add 1 mL of
concentrated sulfuric acid per liter and store at 4 °C.
Before testing the stored sample, warm to room temperature and adjust the
pH to 3–10 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. Enter 4427 mg/L NO
3
(1000-mg/L NO
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 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
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.
Pb
2+
, Zn
2+
, Ni
2+
, Hg
2+
, Fe
3+
, Cd
2+
, Sn
2+
,
Ca
2+
, Cu
2+
50 mg/L
Co
2+
, Fe
2+
10 mg/L
Cr
6+
5 mg/L
NO
2
–
2 mg/L
Ion No interference up to:
Interfering Substance Interferes above:
COD 200 mg/L (high bias)
Nitrite 2 mg/L (high bias)
Chloride 500 mg/L (low bias)