pH meter- Instrumentation,Calibration and operation,types and applications

1. pH Meter
Dr Sumitha J
Associate Professor
JBAS College for Women,Chennai-18

2. The scienti
fi
c instrument that measures the hydrogen-ion
concentration in solutions.
The solutions with a pH less than 7 are termed acidic and when it is
more than 7, it is called alkaline.
The pH meter measures the difference in electrical potential between a
pH electrode and a reference electrode

3. pH meters measure the voltage between two electrodes
It consists of pair of electrodes or a combination electrode, an
ampli
fi
er to read the potential difference and a display unit.
The electrodes are usually glass and reference electrodes separately
or combined.
The electrodes are inserted into the test solution and the purpose of
the electrode is to measure changes in the potential on the respective
side of the glass membrane.
The resulting voltage will be the potential difference between the two
sides of the glass membrane

5. Glass Electrode
These are rod-like structures usually made of glass, with a bulb
containing the sensor at the bottom.
The glass electrode for measuring the pH has a glass bulb
speci
fi
cally designed to be selective to hydrogen-ion concentration.
On immersion in the solution to be tested, hydrogen ions in the test
solution exchange for other positively charged ions on the glass
bulb, creating an electrochemical potential across the bulb.
The electronic ampli
fi
er detects the difference in electrical potential
between the two electrodes generated in the measurement and
converts the potential difference to pH units

6. Reference Electrode
The reference electrode is insensitive to the pH of the solution,
composed of a metallic conductor, which connects to the display.
This conductor is immersed in an electrolyte solution, typically
potassium chloride, which comes into contact with the test solution
through a porous ceramic membrane.

7. Combination Electrode
Many pH meters use a combination probe, constructed
with the glass electrode and the reference electrode
contained within a single probe.

8. Calibration & Operation
Calibration is performed with two standard buffer solutions that span the
range of pH values to be measured.
Buffers at pH 4.00 and pH 10.00 are suitable for general laboratory
purposes
The pH meter has two calibration controls to set the meter reading equal
to the value of the
fi
rst and second standard buffers.
More precise measurements sometimes require calibration at three
different pH values.

9. Calibration & Operation
A third control allows the temperature to be set. Standard buffer sachets
are used to measure the temperature dependence of the buffer control.
Some pH meters provide built-in temperature-coef
fi
cient correction, with
temperature thermocouples in the electrode probes.
The calibration process correlates the voltage produced by the probe
(approximately 0.06 volts per pH unit) with the pH scale.
After each measurement, the probes are rinsed with distilled
water or deionized water to remove any traces of the solution being
measured, blotted with a wipe to absorb any remaining water to prevent
dilution of the further test sample, and then immersed in a storage solution
suitable for the particular probe type.

10. Types of pH meters
Benchtop pH meters are often used in laboratories and are used to
measure samples which are brought to the pH meter for analysis.
Portable, or
fi
eld pH meters, are handheld pH meters that are used to take
the pH of a sample in a
fi
eld or production site.[19]
In situ pH meters or pH analyzers, are used to measure pH continuously in
a process which could either stand-alone, or be connected to a higher-
level control information system for process control

11. The application of pH meters is wide-ranging from laboratories to R&D
divisions
Chemical Industries
Soil Analysis
Water Analysis
Food Industries
Brewing Industries
Healthcare