D6423_9
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Turn on the pH meter and
allow it to warm up thoroughly
in accordance with the
manufacturer's instructions.
Note the temperature of
the sample to be tested.
If the temperature
compensation is to be manual,
adjust the temperature
dial of the meter
to correspond to the temperature
of the sample to be tested.
And allow time for all buffers,
solutions, and the electrode
to equilibrate thermally.
Clean or rehydrate the
electrode after every 10 samples
and new electrodes
before first use
by alternately soaking four
times in 1 molar sodium
hydroxide solution and
1 molar sulfuric acid,
or 1 molar hydrogen chloride
for about 30 seconds each.
Remove the electrode
and rinse it
with distilled water
into a waste container.
Calibrate the pH
meter to pH 7.00,
with a water-based pH
7.00 buffer solution.
Remove the electrode
and rinse it
with distilled water
into a waste container.
Calibrate the pH
meter to pH 4.00,
with a water-based pH 4.00
buffer solution using the slope
adjustment.
The slope shall be in
the 95% to 100% range,
or the electrode will have
to be cleaned or replaced.
Remove the electrode
and rinse it
with distilled water
into a waste container.
Return the electrode
to the pH 7.00 buffer.
And if the measured pH is
not between 6.90 and 7.10,
then return to subsection
9.2 of the written standard.