Chlorine, Total
Chlorine, Total
ChlorineTot_TNT_Other_DPD_Eng_Ody.fm Page 3 of 4
Sample Collection, Storage and Preservation
Analyze samples for chlorine immediately after collection. Free chlorine and
combined chlorine are strong oxidizing agents and are unstable in natural
waters. Many factors, including reactant concentrations, sunlight, pH,
temperature, and salinity 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 l liter of deionized water) for at least
one 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.
A common error in testing for chlorine is obtaining an unrepresentative 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 containers so there is no headspace (air) above the sample.
Perform the chlorine analysis 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.
Hardness No effect at less than 1,000 mg/L as CaCO
3
Iodine, I
2
Interferes at all levels
Manganese, oxidized
(Mn
4+
, Mn
7+
)
or
Chromium, oxidized (Cr
6+
)
1. Adjust sample pH to 6–7.
2. Add 3 drops Potassium Iodide (30-g/L) (Cat. No. 343-32) to a 25-mL sample.
3. Mix and wait 1 minute.
4. Add 3 drops Sodium Arsenite* (5-g/L) (Cat. No. 1047-32) and mix.
5. Analyze 10 mL of the treated sample as described in the procedure.
6. Subtract the result of this test from the original analysis to obtain the correct
chlorine concentration.
Ozone, O
3
Interferes at all levels
Peroxides May interfere
Extreme sample pH or highly
buffered samples
Adjust to pH 6–7 using acid (Sulfuric Acid, 1.000 N, Cat. No. 1270-32) or base (Sodium
Hydroxide, 1.00 N, Cat. No. 1045-32).
* Samples treated with sodium arsenite for manganese or chromium interferences will be hazardous wastes as regulated by the
Federal RCRA for arsenic (D004). See Section 4 for more information on proper disposal of these materials.
(continued)
Interfering Substance Interference Levels and Treatments
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