Hanna Instruments HI 9828, Instruction Manual, Page: 13 / 60

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1.5.3 pH and pH/ORP sensors
As mentioned before HI 9828 is predisposed for pH and
ORP measurements.
HI 769828PH and HI 769828PHO are probes with pH
and pH/ORP sensors respectively. See the table below for
electrodes specifications.
Reference Junction Electrolyte Tip Body material
p H double cloth gel spheric PEI
O R P double cloth gel Pt PEI
To avoid clogging problems and ensure a fast response, the pH bulb must be
kept moist at any time. Store the electrode with few drops of HI 70300L storage
solution.
To make correct redox measurements the following conditions must prevail:
• The surface of the electrode must be cleaned and smooth.
• The surface of the electrode must undergo a pretreatment in order to respond
quickly.
Because the Pt/PtO system depends on the pH, the pretreatment of the elec-
trode may be determined by the pH and the redox potential values of the solution
to be measured.
As a general rule, if the ORP mV reading corresponding to the pH value of the
solution is higher than the values in the table below, an oxidizing pretreatment is
necessary; otherwise a reducing pretreatment is necessary:
pH mV pH mV pH mV pH mV pH mV pH mV
0 990 1 920 2 860 3 800 4 740 5 680
6 640 7 580 8 520 9 460 10 400 11 340
12 280 13 220 14 160
For reducing pretreatment: immerse the electrode for a few minutes in HI 7091L.
For oxidizing pretreatment: immerse the electrode for a few minutes in HI 7092L.