Hach DR/850, Procedures Manual, Page: 102 / 460

102
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 which may have a large chlorine
demand.
•
Pretreat glass sample containers to remove chlorine demand
by soaking in a dilute bleach solution (1 mL of commercial
bleach to 1 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.
•
Use separate, dedicated sample cells for free and total
chlorine determinations. If trace iodide from the total
chlorine reagent is carried over to the free chlorine test,
monochloramine could interfere.
5.
Press:
ZERO
The cursor will move to
the right, then the
display will show:
0.0 mg/L Cl
2
6.
Remove the sample
cell from the cell holder
and add the contents of
one 25-mL DPD Free
Chlorine Reagent pillow
to the sample. Cap and
shake the sample cell
about 20 seconds to
dissolve.
Proceed immediately to
step 7 .
Note: A pink color will
develop if chlorine is
present.
7.
Place the sample cell
into the instrument.
Cover the sample cell
tightly with the
instrument cap.
Note: Place the sample cell
into the cell holder as
illustrated. The sample cell
tab should be at the 6-
o’clock position and
completely seated in the
cell holder slot.
8.
Within one minute
after reagent addition,
press:
READ
.
The cursor will move
to the right. The result in
mg/L chlorine (as Cl
2
)
will be displayed.
Note: See “Interferences”
on page 104 for samples
with high monochloramine
concentrations.
Tab
Slot
CHLORINE, FREE, Ultra-high Range, continued