pH meter or pH tester is an electrical and analytical device used to measure the acidity or alkalinity of liquids and semi-solids.
pH is a common unit that measures the acidity or alkalinity of a solution using a logarithmic scale.
The solution becomes neutral if the value of pH is 7 where lower values are more acidic, and higher ones are more alkaline.
It is defined as the negative logarithm of hydrogen ion concentration [H+] which gives in moles per liter (c).
pH = -log10 [H+]
The product of hydrogen ion concentration[H+] and hydroxyl ion concentration [OH-] is constant in an aqueous solution and the pH is equal to the negative logarithm of the concentration of hydrogen ions.
pH Meter
A pH meter or pH tester is one kind of scientific instrument and statistical tool that measures the hydrogen-ion activity in water-based solutions and determines its acidity or alkalinity expressed as pH. It measures the pH in the solution on a scale of 0 to 14. This meter is also called as a “potentiometric pH meter” since it gauges the difference in electrical potential between a pH electrode and a reference electrode.
It is very essential to monitor the pH for manufacturing specific foods, the culture medium, soil, chemical solutions, quality control, etc.
The working principle of pH Meter
The digital pH meter working activities depend on the ions exchange from the sample solution which is tested to the inner solution of the glass electrode via the glass membrane. The probe of the pH meter conducts the electrical signals which then display the pH value of the solution. One solution is filled with a buffer pH 7 and the other with saturated potassium chloride solution. The sensor of the electrode bulb contains a porous glass membrane which coated with metal salts and silica.
The pH probe must be submerged in a sample solution for measuring the pH. Then hydrogen ions build up around the electrode bulb and take the place of the metal ions. Some of the metal ions made up around the bulb and take the place of the metal ions. A small amount of transfer takes place of metal ions from the glass (sensor) electrode to the sample solution for lower sensitivity to pH changes or complete insensitivity to pH changes, the reference electrode potential offers a constant voltage.
As a result, some electricity production takes place which is captured by the silver wire by generating potential difference (hydrogen-ion activity). The pH meter can convert the voltage of this electric flow into pH value by helping the generated voltage to the reference electrode.
The voltage can be raised at the time of increasing the solution’s acidity resulting in a higher concentration of hydrogen ions. It may reduce the voltage and raises the pH reading on a pH meter if the concentration of hydroxyl ions increases.
The instrumentation of the pH meter
A pH meter consists of the following three basic elements:
Input impedance meter
It is a very important part that holds the microprocessor. It processes extremely small electrode voltages and displays measurements in pH units on display. A microchip in this meter reads the pH of the solution, calculates the measurement temperature, and helps to translate the amplifier voltage value.
The combined electrode
This part of the pH meter comprises two electrodes, where the actual measurement takes place. This is the most expensive, sensitive, and consumable component of this pH meter that needs to be handled properly and carefully. A measuring electrode or sensor electrode and a reference electrode submerged in the same solution, make up the combination electrode. It requires stable voltage for the reference electrode to produce a defined pH value of the measured solution.
Reference electrode
This electrode is made from a reference material such as mercury, mercury chloride, and a saturated solution of potassium chloride that is submerged in a definite electrolyte solution which needs to be reacting with the measured solution most frequently through a porous ceramic junction, has a low electrical resistance due to having a high ion concentration and adequate stability across a broad temperature range.
pH glass electrode
This part also known as a sensor electrode or indicator electrode consists of a glass bulb sensitive to hydrogen ions, and when the relative concentration of hydrogen ions within and outside the bulb changes, so does the mili volt output.
Amplifier
This part of the pH meter also known as a voltage amplifier, plays an important role in measuring pH value. It will increase the accuracy of the pH reading in the same way that a thermometer increases calculations concerning temperature. It ensures the amount of acidity, basicity, and neutrality in a solution in the pH range of 0–14.
Thermometer probe
There have some pH meters that can measure the temperature of the solution being sampled and incorporate that information into the meter reading. This modern system is termed “Automatic Temperature Compensation (ATC)”.
Applications of pH meter
A pH meter is a very important analytical instrument for assessing soil in the agricultural sector. It requires because major crops need an alkaline climate. Moreover, they can be utilized to gauge the pH of the soil, which will aid in maximizing returns and yields from the soil. This testing instrument is essential to monitor the pH level in water treatment facilities and RO water purifiers. There have various chemical industries use pH meters to neutralize wastewater from the steel, pharmaceutical, pulp, paper, biotech, and petrochemical industries.
This instrument determines the pH value of chemical compounds and food products to ensure us their safety and quality. It is a very emergency tool in the context of dairy products in the food industry. It helps to measure the pH of biological fluids such as blood, urine, gastric acid, etc. for various biological conditions. The pH meter is very useful for the manufacturing of detergent.
Advantages of using pH Meter
This analytical tool is well-matched for continuous automatic recording and control of industrial and commercial processes. It produces rapid and reproducible measurements to control and operate.
It is very much used for both oxidizing and reducing solutions without creating any effect. This tool is suitable for use in colloidal, turbid, and colorful solutions. We get the most accurate and precise value of pH from this device. Anyone can be easily used everywhere while traveling because it is portable.
Disadvantages of using pH Meter
It requires cleaning regularly to avoid possible contamination of the tested samples. It will get damaged if exposed to corrosive chemicals. The output readings of the pH meter show various problems if a higher temperature exists. It should be calibrated before use to get accurate results unless our results may be distorted. It requires a buffer solution to calibrate the pH meters.
References
1.McLean, A. J. (2017). pH meter. Academic Psychiatry, 41, 769-769.
2.Pecsok, R. L. (1951). An experiment for the pH meter. Journal of Chemical Education, 28(5), 252.
