Hach DR2400 - Page 506

Nitrogen, Total
Nitrogen, Total
Page 6 of 8
NitrogenTot_TNT_Other_PSD_Eng_Ody.fm
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 an Ammonia Nitrogen Voluette
®
Ampule Standard
Solution, 1000-mg/L as NH
3
–N.
5. Prepare three sample spikes. Fill three mixing cylinders with 50 mL of
sample. Use the TenSette
®
Pipet to add 0.1, 0.2, and 0.3 mL of standard,
respectively, to each sample and mix thoroughly.
6. Add 2 mL of each prepared solution, respectively, to three Total Nitrogen
Hydroxide Reagent Vials.
7. 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. The
nitrogen concentration should increase by approximately 2, 4, and 6 mg/L N,
respectively.
8. 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
1. For proof of accuracy, substitute 2 mL of a 10-mg/L ammonia nitrogen
standard solution for the sample in the procedure. A single analyst should
obtain less than 5% variation on replicates.
2. To adjust the calibration curve using the reading obtained with the
10-mg/L N standard solution, touch
Options on the current program menu.
Touch
Standard Adjust.
3. Touch
On. Touch Adjust to accept the displayed concentration (the value
depends on the selected chemical form). If an alternate concentration is used,
touch the number in the box to enter the actual concentration, then touch
OK.
Touch
Adjust.
See Section 3.2.4 Adjusting the Standard Curve on page 40, for more information.