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WARNING!
CORROSIVE SUBSTANCE
The solution used during the following check is an acid and should be handled with care.
Follow the manufacturer's directions. Wear the proper protective equipment. If contact with
skin or clothing is made, immediately rinse with plenty of clean water.
Type 2: A second ORP standard solution can be prepared from the following recipe:
Procedure
1.
2.
3.
This standard ORP solution, although not as simple to prepare as the quinhydrone recipe,
is much more stable and will maintain its millivolt value for approximately one year when
stored in glass containers. This solution (ferric/ferrous ammonium sulfate) produces a
nominal ORO of 476 +20 mV at 25 ºC when used with a saturated KCL/AgCl reference
electrode and platinum measuring electrode. Some tolerance in mV values is to be
expected due to the rather large liquid reference junction potentials that can arise when
measuring this strongly acidic and concentrated solution. However, if measuring
electrodes are kept clean and in good operating condition, consistently repeatable
calibrations can be carried out using this standard solution.
4.3.2
Cleaning Platinum Electrode
To restore the electrode to normal operation, clean the platinum electrode with baking
soda. Polish it by rubbing it with a damp paper towel and baking soda until a bright, shiny
appearance is attained.
Instruction Manual
Dissolve 39.2 grams of reagent grade ferrous ammonium sulfate, Fe(NH
6H
O and 48.2 grams of reagent grade ferric ammonium sulfate, FeNH
2
H
O in approximately 700 ml of water (distilled water is preferred but tap water is
2
acceptable).
Slowly and carefully add 56.2 ml of concentrated sulfuric acid.
Add sufficient water to bring the total solution volume up to 1000 ml.
Maintenance
●
)
(SO
)
4
2
4
2
● 12
(SO
)
4
4
2
29
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