Principle of operation and operating mode of the pH meter

Know the principle, types and procedure of the pH meter used to measure the activity of hydrogen ions (acidity or alkalinity) in solution.

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What is a pH meter?

A pH meter is an automated measuring tool used to determine the pH of a liquid. It is also known as a potentiometric pH meter because it determines the electrical potential difference between a pH electrode and a reference electrode.

You can get a rough idea of ​​pH by using indicators, pH papers, or litmus papers that change color depending on the pH level. These types have limitations in their accuracy and can be difficult to interpret correctly. Therefore, a pH meter is widely used to determine the exact pH of the sample solution.


  1. What is the pH meter?
  2. Principle of operation of the pH meter
  3. Type of pH meter
  4. pH meter procedure
  5. pH meter applications
  6. Advantages of the pH meter
  7. Disadvantages of the pH meter
  8. FAQs

A pH meter consists of an electrode connected to an electronic meter that monitors and displays the correct pH reading. A glass electrode made of a specialized glass membrane is sealed at the end to form a bulb. An internal standard acidity solution, typically 0.1 M hydrochloric acid (HCl), and an internal reference electrode, REin (often an Ag/AgCl wire electrode), are encased in glass. This solution is known as the reference solution, which has a pH of 07.00.

A second electrode, REjob, is inserted into an outer tube soaked in potassium chloride (KCl). Around the first closed glass tube containing the 0.1 M HCl, this outer tube forms a concentric enclosure. This configuration is known as a combination pH electrode.

Principle of operation of the pH meter:

principle of the pH meter

The pH meter works primarily on the assumption that the interface between two liquids produces an electrical potential that can be determined. The principle of operation of the pH meter is based on the exchange of ions from the liquid sample through the glass membrane to the internal solution of a glass electrode. The porosity of the glass membrane decreases with its constant use, which reduces the performance of the probe.

It detects the voltage difference between the two electrodes, i.e. the glass electrode and the reference electrode. When both electrodes are present, the electrode is called a combined electrode and is placed in the solution to be tested.

These two electrodes are immersed in a solution, then the H+ ions of the solution to be tested are exchanged for other positively charged ions present in the crystal ball. Therefore, there is an action between these extra ions in the solution and the H+ ions or positively charged ions present in the glass bulb.

The electric potential difference between the two electrodes is detected by the amplifier. The unit of pH is the difference between these potentials. The electric potential difference between the two electrodes is detected by the amplifier. The difference in potential is known as the unit of pH.

Type of pH meter:

The pH meter ranges from simple and inexpensive pen-shaped devices with computer interfaces to complex and expensive laboratory devices, where many inputs are recorded for indicators and temperature measurements to manage variations in pH due to temperature. The display can be digital and the systems can be battery powered or rely on the power supply.

There are special pH meters which can be used in particular applications allowing the determination of the pH by colorimetry. Commercial pH meters are available based on solid-state electrodes, rather than traditional glass electrodes.

pH meter procedure:

Before starting a pH meter process, we need to recognize the different parts that are essential to complete the process. A pH meter consists of three main parts, such as pH electrode or glass electrode or combination electrode, temperature probe and electronic control unit.

pH electrode:

Glass electrodes are the most commonly used pH electrodes made of special glass. Silver/silver chloride (Ag/AgCl) is the most common form of reference electrode used today.

Temperature sensor:

For accurate pH determination, some pH meters automatically compensate for temperature. This is achieved by means of a meter, temperature probe, which together with the electrode is immersed in the sample solution.

Electronic control unit:

To produce a chemical signal, the electrode reacts to the concentration of hydrogen ions in the sample solution. This signal is then transformed into pH values ​​which are displayed on the screen.

pH measurement procedure:

  • The pH meter should be calibrated with the appropriate buffer solution, such as pH 07.00, 04.00 and 09.20 to confirm the performance of the pH electrode before pH measurement. The process can vary somewhat depending on the pH meter used and the electrode used, but in most cases the process for determining pH is very similar.
  • Clean the electrode and temperature probe with deionized water and wipe gently with soft tissue paper.
  • Immerse the electrode in the sample solution.
  • Press the pH mode key on the panel.
  • The instrument will display the pH.
  • Save the reading or print it if the printer is connected.
  • Restart the instrument and clean the electrode and temperature probe again with distilled water and wipe gently with soft tissue paper.

Applications of the pH meter:

  • The basic application of the pH meter allows us to determine whether a liquid sample is acidic, basic or neutral.
  • pH is mainly used in the pharmaceutical, beverage, chemical and food industries.
  • It is commonly used in chemistry to determine the acidity or basicity of a substance.
  • It is used in production to ensure product quality.
  • pH is widely used in research and development in many fields.
  • pH is very important for checking the consistency of water, soil and pesticides in the agricultural sector.
  • The pH meter is an improved version for pH determination over traditional methods, providing easy and accurate pH.

Advantages of the pH meter:

  • This makes pH measurement quick and easy.
  • The advantage of pH meters is that they are compact and portable (pen pH meter) that you can use in another place.
  • It can be used for a wide variety of applications.
  • This indicator provides an accurate pH value compared to pH paper and indicators.
  • It covers the entire pH range, i.e. from 01 to 14.
  • By using a standard buffer solution, you can calibrate the pH meter to improve consistency.

Disadvantages of the pH meter:

  • Deposit on the membrane of the electrode may cause an error in the results.
  • Due to the fragility of the glass electrodes, there is a risk of breakage.
  • It is often necessary to calibrate the pH meter.
  • To calibrate the pH meter, you need buffer solutions which make it expensive.

Frequently asked Questions:

What is the pH meter?

A pH meter is a device used to determine the acidity or alkalinity of a solution. pH is a measure of hydrogen ion concentration.

What is the basic principle of the pH meter?

A pH meter gives information on the degree of acidity or alkalinity of a solution. Measurement of the concentration of hydrogen ions in the basic principle of the pH meter.

Why calibrate a pH meter?

To avoid drift and maintain the accuracy of the pH meter, it is necessary to periodically calibrate the pH.

Why are buffer solutions used to calibrate the pH meter?

Buffer solutions are used to calibrate a pH meter, avoiding changes in pH. You can adjust the pH value by using the standard buffer solution of known pH.

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