33
INTERFERENCES
A positive interference may be caused by:
Bromine (Br
2
)
Iodine (I
2
)
Oxidized forms of Chromium and Manganese
Ozone (O
3
)
Alkalinity above 250 mg/L CaCO
3
or acidity above 150 mg/L CaCO
3
will
not reliably develop the full amount of color or it may rapidly fade. To
resolve this, neutralize the sample with diluted HCl or NaOH.
In case of water with hardness greater than 500 mg/L CaCO
3
, shake
the sample for approximately 2 minutes after adding the powder
reagent.
Chlorine, Total
48
•
Choose a homogeneous sample. Samples containing settleable solids
need to be homogenized with a blender.
•
Preheat the Hanna Reactor C 9800 to 150 °C (302°F). For correct
use of the reactor follow Reactor Instruction Manual.
Use of the optional HI 740217 safety shield is strongly recommended.
Do not use an oven or microwave because leaking samples can
generate a corrosive and possibly explosive atmosphere.
• Remove the cap from two Reagent Vials.
• Add exactly 2.0 mL of sample to one vial (sample vial), and 2.0
mL of deionized water to the other vial (blank vial), while keeping
the vials at a 45-degree angle. Replace the cap tightly and mix
by inverting each vial a couple of times.
Warning
: as the vials become hot during mixing, be careful in
handling them.
•
Insert the vials into the reactor and
heat them for 2 hours at 150°C.
•
At the end of the digestion period
switch off the reactor. Wait for twenty
minutes to allow the vials to cool to
about 120°C.
• Invert each vial several times while
still warm, then place them in the test
tube rack.
Warning
: as the vials are still hot, be
careful in handling them.
•
Leave the vials in the tube rack to cool
to room temperature. Do not shake or
invert them anymore otherwise the
samples may become turbid.
COD LR