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Sample Collection, Preservation, and Storage
Accuracy Check
Nitrate_UniCell_Dimeth_Eng_Ody.fm
Ion
2+
2+
2+
2+
3+
Pb
, Zn
, Ni
, Hg
, Fe
2+
2+
Ca
, Cu
2+
2+
Co
, Fe
6+
Cr
–
NO
2
Interfering Substance
COD
Nitrite
Chloride
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.
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
. Touch
Options
additions procedure will appear.
3. Enter 4427 mg/L NO
4. Touch
to accept the default values for sample volume, and spike volumes.
OK
Touch
to change these values. After values are accepted, the unspiked
Edit
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
. Each addition should reflect approximately 100% recovery.
Read
7. After completing the sequence, touch
the standard additions data points, accounting for matrix interferences. Touch
, then select
View: Fit
the sample spikes and the "Ideal Line" of 100% recovery.
See Section 3.2.2 Standard Additions on page 32 for more information.
2+
2+
, Cd
, Sn
,
. A summary of the standard
Standard Additions
(1000-mg/L NO
–N) as the standard concentration.
3
3
Graph
and touch
Ideal Line
OK
Nitrate
No interference up to:
50 mg/L
10 mg/L
5 mg/L
2 mg/L
Interferes above:
200 mg/L (high bias)
2 mg/L (high bias)
500 mg/L (low bias)
to view the best-fit line through
to view the relationship between
Page 3 of 4
Nitrate
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