pH meter, pH

1. What is a PH meter?
Theory of operation
Electrode
Operation modes

2. What is a PH meter?
 The pH meter is a laboratory equipment which used to
measure acidity or alkalinity of a solution.
 pH = -log [H+]
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pH = 4.0 acidic solution
pH = 7.0 neutral solution
pH = 10.0 basic solution
0< pH <14
 The pH meter measures the concentration of hydrogen ions
[H+] using an ion-sensitive electrode.

3. Theory of operation
Operation is similar to galvanize cell,

4. Electrode or pH probe

5. Different operating modes
a) Standby mode -In this position the electrodes are protected from
electrical currents. It is the position used for maintaining the
equipment while stored.
b) pH mode- In this position the equipment can take pH
measurements after performing the required calibration procedures
c) Millivolt mode (mV).In this position the equipment is capable
of performing millivoltage readings.
d) ATC mode- The Automatic Temperature Control mode is used
when the pH is measured in solutions for which the temperature
varies. This function requires the use of a special probe. Not all pH
meters have this control.

6. Calibration
a) One point calibration- This is carried out for normal
working conditions and for normal use. It uses one
known pH reference solution.
b) Two point calibration - This is done prior to
performing very precise measurements. It uses two
known pH reference solutions.
 Necessary calibrating steps are described in each
operating manuals and it should be carried out
according to manufacturer instructions.

7. Calibration
One point calibration
Two point calibration
 Adjust the temperature selector
 Adjust the temperature selector to the
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to the environmental
temperature.
Rinse the electrode with distilled
water in an empty beaker.
Dry the electrode
Place electrodes in the
calibration solution. (pH=7.0)
Adjust the meter to read the pH
of the calibration solution using
the button marked Cal
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environmental temperature.
Rinse the electrode with distilled water in
an empty beaker.
Dry the electrode
Place electrodes in the first calibration
solution. (pH=4.0)
Adjust the meter to read the pH of the
calibration solution using the button
marked Cal 1
Rinse the electrode with distilled water
Dry the electrode
Place electrodes in the first calibration
solution. (pH=10.0)
Adjust the meter to read the pH of the
calibration solution using the button
marked Cal 2

8. Measuring the pH of a solution
a)
b)
c)
d)
e)
Rinse the electrode with distilled water and dry it.
Place the electrode in the solution of unknown pH.
Turn the functions selector from the Standby
position to the pH position.
Read the pH of the solution on the meter’s scale or
the screen.
Turn the functions selector again to the Standby
position.

9. General Maintenance
pH Electrode : Every four
 Replace Electrolyte solution (KCl)
month the electrode considering affected
 Clean
pHand evaluate its:general physical
Analyzer’s Every six month
a)

b)
c)
d)
contaminants
General cleaning- Soak the pH electrode
in a 0.1 M HCl solution or 0.1 M HNO3,
for 20 minutes. Rinse with water.
Removal of deposits and bacteria- Soak
the pH electrode in a diluted domestic
bleach solution, for 10 minutes. Rinse
abundantly with water
Cleaning oil and grease- Rinse the pH
electrode with a mild detergent or with
methyl alcohol. Rinse with water.
Cleaning of protein deposits- Soak the
pH electrode in 1% pepsin and 0.1 M HCl
for 5 minutes. Rinse with water.
 Examine the exterior of the equipment
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condition.
Test the connection cable and its
system of connections.
Examine the equipment controls.
Verify that these are in good condition
and activated without difficulty.
Verify the state of the electrode
carrying arm.
Check the batteries (if applicable);
change them if necessary.
Test its function by measuring the pH
of a known solution
Inspect the ground connection and
check for escaping current

10. Basic fault Identification
 1.0 The pH meter shows
unstable readings.
 2.0 The electrode’s response
is slow.

11. 1.0 The pH meter shows unstable readings.
There are air bubbles in
the electrode.
The electrode is dirty.
The electrode is not
immersed.
 Soak the electrode to eliminate the
bubbles.
 Clean the electrode and recalibrate.
 Verify that the sample covers the tip of the
electrode perfectly.
The electrode is broken.

12. 2.0 The electrode’s response is slow.
The electrode is dirty or
greasy.
 Clean the electrode and recalibrate.

13. 3.0 The screen shows a calibration or error message.
There is a calibration
error.
 Recalibrate the pH meter.
The calibration of the
 Verify the buffer values used
buffer value is erroneous.
The electrode is dirty.
 Clean and calibrate the electrode.

14. End of pH Meter