Hach DR2400 - Page 757

Surfactants, Anionic (Detergents)
Surfactants, Anionic (Detergents)
Detergents_None_Other_CVI_Eng_Ody.fm Page 3 of 4
Interferences
Sample Collection, Storage, and Preservation
Collect samples in clean plastic or glass bottles. Analyze samples as soon as
possible, but they may be stored at least 24 hours by cooling to 4 °C (39 °F).
Warm to room temperature before testing.
Accuracy Check
Standard Additions Method (Sample Spike)
1. After reading test results, leave the sample cell (unspiked sample) in the
instrument. Verify that the units displayed are in mg/L.
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 Detergent Voluette
®
Ampule Standard, 60-mg/L LAS.
5. Prepare three sample spikes. Fill three beakers with 300 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.
Note: The anionic surfactant reading should increase 0.02 mg/L for every 0.1 mL of
standard added.
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.
Interfering Substance Interference Levels and Treatments
Chloride
High amounts of chloride, such as those levels found in brines
and seawater, will cause low results.
Perchlorate ions Interferes at all levels.
Periodate ions Interferes at all levels.