Hach DR2400 - Page 294

Formaldehyde
Formaldehyde
Page 4 of 6
Formaldehyde_PP_Other_MBT_Eng_Ody.fm
Standard Additions Method (Sample Spike)
1. After reading test results, leave the sample cell (unspiked sample) in the
instrument.
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 Formaldehyde Voluette
®
Ampule Standard, 4000-mg/
LCH
2
O.
5. Use a TenSette
®
Pipet to add 0.2 mL of the standard to a 100-mL volumetric
Class A flask. Dilute to volume with formaldehyde-free water and mix well.
Prepare daily. This is an 8000-µg/L (8-mg/L) formaldehyde standard.
6. 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 8000-µg/L standard, respectively, to each sample and mix
thoroughly.
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.
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
Prepare a 320-µg/L Formaldehyde Standard Solution by pipetting 1.0 mL of the
8000-µg/L solution from the Accuracy Check into a 50-mL mixing cylinder. Dilute
to 25.0 mL with formaldehyde-free water. Run the test directly on this sample.
Method Performance
Precision
Standard: 300 µg/L CH
2
O
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
See Section 3.4.5 Sensitivity on page 44 for more information.
Summary of Method
Program 95% Confidence Limits of Distribution
200 285–315 µg/L CH
2
O
Portion of Curve ∆Abs ∆Concentration
Entire range 0.010 3 µg/L CH
2
O