Hach DR2400 - Page 436

Nitrate
Nitrate
Page 4 of 6
Nitrate_PP_Low_CDR_Eng_Ody.fm
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 Nitrate Nitrogen Voluette
®
Ampule Standard, 12.0-mg/L
NO
3
–
–N (Cat. No. 14333-10).
5. Prepare three sample spikes. Fill three mixing cylinders (Cat. No. 1896-40)
with 15 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
1. To test accuracy, use a 0.20-mg/L NO
3
–
–N standard in place of the sample
and perform the procedure as described. Prepare this standard by diluting
2.00 mL of a 10-mg/L Nitrate Nitrogen Standard Solution to 100.0 mL with
deionized water.
2. To adjust the calibration curve using the reading obtained with the
0.20-mg/L nitrate nitrogen standard, 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.