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PROCEDURE :
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PRECAUTION
Use
only tissue paper to wipe the glass electrode.
Ensure
that the electrode is always dipped in tap water.
Do not
dip pH electrode in distilled water as this will cause ions to leach out of
the glass membrane of electrolyte, causing a slow and sluggish response.
Keep
the switch of the instrument on 'Stand by' mode when the instrument is not in
use.
Prepare
the buffer solutions weekly + 2 days.
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OPERATION:
pH
meter Instrument Consists of following units,
1. The
main Digital
Instrument.
2. The
Electrode (Glass and Reference Electrode in single
entity).
Switch
ON the mains supply, Press ON/OFF button once to start the meter.
Ensure
that the instrument is calibrated.
Remove
the electrode from tap water.
Clean
the electrode with distilled water 2 to 3 times.
Rinse
electrode in a waste beaker.
Soak
the excess water with tissue paper.
Avoid
rubbing the electrode as it has a sensitive membrane around it.
Adjust
the `Temperature' knob to Room Temperature.
Immerse
the electrode in sample solution which is to be tested and Stir the solution.
Push
the second switch for `Read'
mode.
Allow
stabilizing the pH and then record the pH.
The
display shows the pH of sample solution.
After
completion of pH measurement rinse the electrode with distilled water.
Dip
the electrode in tap water.
After
measurement enter details in usage log book.
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CALIBRATION
PROCEDURE:
Calibrate
the pH meter with Standard buffer solutions.
Prepare
standard Buffer solutions from buffer capsules.
Buffer Solution
pH 4.00 :
Open a
capsule by twisting and pulling apart.
Dissolve
the content in 10 ml of distilled water.
Make up
the volume up to 100 ml with distilled water.
This
solution will have pH 4.00 + 0.05.
Buffer
Solution pH 7.00 :
Prepare
the buffer solution pH 7.00 same as above.
This
solution will have pH 7.00 + 0.05.
Buffer
Solution pH 9.20 :
Prepare
the buffer solution pH 9.20 same as above.
This
solution will have pH 9.20+ 0.05.
Pour
the buffer solutions into individual bottles for calibration and label it.
Calibrate
the pH meter with above Buffer solutions at 25°C
(±2°C).
The
first will be a “Neutral” buffer with a pH of 7.00.
Immerse
the electrode in buffer solution pH 7.00.
Push
the second switch for `Read' mode and adjust the pH 7.0(Limit: 6.95 to 7.05)
with the help of 'STAND (pH 7)' knob.
Remove
the electrode from the buffer solution pH 7.00.
Rinse
the electrode with Distilled water and wipe with tissue paper.
Immerse
the electrode in buffer solution pH 4.00.
Push
the second switch for `Read' mode and check if display indicates 4.00 pH. If
there is an error, adjust the 'SLOPE' knob to read 4.00 pH(Limit: 3.95 to
4.05).
Repeat
the steps 5.3.7 and 5.3.10 till the instrument reads 7.00 pH and 4.00 pH.
Rinse
the electrode with Distilled water and wipe with tissue paper after
both pH adjusted.
Check
the buffer solution pH 9.20(Acceptance Criteria: + 0.05).
Note
down all observed pH in format for daily pH calibration.
After
completion of pH measurement rinse the electrode with distilled water and
dip the electrode in tap water.
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REGENERATION
OF ELECTRODE:
The pH
glass membrane, the probe tip, is the sensitive part of electrode. If the
glass membrane dries out during storage and sometimes after a rough cleaning
procedure gets damaged so it is necessary to restore the hydrated glass
layer. which is restored by Regeneration.
For the
Regeneration follow the procedure given
below,
Soak
the pH electrode in 0.1 M HCl for 12 hours.
Rinse
the electrode carefully with distilled water.
Soak
the electrode in buffer pH 4.00 for about one hour.
Rinse
the electrode with distilled water and deep the electrode in tap water.
Do
Regeneration half monthly + 2 days.
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