Chlorine, Free
Chlorine, Free
ChlorineFre_MP_High_DPD_Eng_2400.fm Page 3 of 4
Sampling and Storage
Analyze samples for chlorine immediately after collection. Free chlorine is a
strong oxidizing agent and reacts rapidly with various compounds. Many
factors such as sunlight, pH, temperature and sample composition will influence
decomposition of free chlorine in water.
Avoid plastic containers since these may have a large chlorine demand. Pretreat
glass sample containers to remove any chlorine demand by soaking in a dilute
bleach solution (1 mL commercial bleach to 1 liter of deionized water) for at least
1 hour. Rinse thoroughly with deionized or distilled water. If sample containers
are rinsed thoroughly with deionized or distilled water after use, only occasional
pre-treatment is necessary.
Do not use the same sample cells for free and total chlorine. If trace iodide from
the total chlorine reagent is carried over to the free chlorine test,
monochloramine could interfere. It is best to use separate, dedicated sample cells
for free and total chlorine determinations.
A common error in testing for chlorine is obtaining a representative sample. If
sampling from a tap, let the water flow for at least 5 minutes to ensure a
representative sample. Let the container overflow with the sample several times,
then cap the sample container so there is no headspace (air) above the sample. If
sampling with a sample cell, rinse the cell several times with the sample, then
carefully fill to the 5-mL mark. Proceed with the chlorine test immediately.
Accuracy Check
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 keypad will appear. Enter the
average chlorine concentration shown on the certificate enclosed with the
chlorine voluette ampules. Touch
OK.
3. A summary of the Standard Additions procedure will appear. Touch
OK to
accept the values for standard concentration, sample volume, and spike
volumes as shown. 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. Open a High Range Chlorine PourRite
®
Ampule Standard, 50–70 mg/L.
5. Prepare three sample spikes. Fill three mixing cylinders (Cat. No. 1896-40)
with 5-mL of sample. Using the TenSette
®
Pipet, add 0.1 mL, 0.2 mL and
0.3 mL of standard, respectively, to each sample and mix thoroughly.
Ozone Interferes at all levels
Peroxides May interfere
Extreme sample pH or highly
buffered samples
Adjust to pH 6–7 using acid (Sulfuric Acid, Cat. No. 1270-32) or base (Sodium Hydroxide,
Cat. No. 1045-32).
* Samples treated with sodium arsenite for interferences will be hazardous waste as regulated by the Federal RCRA for arsenic
(D004). For information on pollution prevention and waste management, refer to Section 4.
Interfering Substance Interference Levels and Treatments
To Next Page
Loading...
