Hach DR/850, Procedures Manual, Page: 120 / 460

120
Sampling and Storage
Analyze samples for chlorine immediately after collection. Free
chlorine is a strong oxidizing agent, and it is unstable in natural
waters. It reacts rapidly with various inorganic compounds and
more slowly oxidizes organic compounds. 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 1
hour. Rinse thoroughly with deionized or distilled water. If
sample containers are rinsed thoroughly with deionized or
distilled water after use, only occasional pretreatment 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 into the
free chlorine determination, monochloramine will interfere. It is
best to use separate, dedicated sample cells for free and total
chlorine determinations.
9.
Press:
READ
The cursor will move to
the right, then the result
in mg/L chlorine will
be displayed.
Note: Standard Adjust may
be performed using a
prepared standard
(see Section 1).
Note: If the sample
temporarily turns yellow
after reagent addition, or
the display flashes “limit”,
it is due to high chlorine
levels. Dilute a fresh
sample and repeat the test.
A slight loss of chlorine
may occur during dilution.
Multiply the result by the
dilution factor; see
Section 1.
CHLORINE, FREE
continued