pH Meter | Principle, Calibration, and Working

A pH meter is used to measure the acidity and alkalinity of a solution, or a pH meter is an electronic device used for measuring the pH of any solution. pH Meter Calibration is required at regular intervals or as per the defined frequency to maintain its accuracy.

pH Meter Principle

It measures the voltage between the two electrodes. One is a glass electrode, and the other is a reference electrode. It displays the result of that voltage that is related to the corresponding pH value.

Sometimes, if both electrons are present, it is called the combination electrode, and they are inserted into the solution in which pH is to be tested. These two electrodes are immersed and, after immersing these electrodes in a solution. That H+ ion in the test solution exchange for other positively charged ions presents on the glass ball. So there is an action between these plus ions of the solution and H+ions or positively charged ions present on the glass bulb. The amplifier detects the difference in electric potential between the two electrodes. The contrast of these potentials is called the ph unit.

Why Range of pH (1 to14)

pH always measured between (1 to14). The solution having the pH=1 is called an acidic solution, or generally, it is highly acidic. The solution with the pH=14 is highly alkaline, or it is a natural solution than the solutions having more H+ ion concentration. It is highly acidic, and the solutions with more OH– ion are highly basic or highly alkaline.

Key components or parts of pH instrument

It consists of a probe, typically a three-in-one combination. The electrode has a hydrogen ion-sensitive glass electrode, a reference electrode, and a temperature probe. The temperature probe is used to ensure any temperature variation is corrected automatically.

At the tip of the probe is a sensitive glass bulb that detects the acidity or basicity of the solution and at the other end of the probe is a high input electronic meter that measures and displays the pH.

pH meter parts image credit: http://web.iyte.edu.tr/

It has a voltmeter attached to a pH electrode because whatever those electrodes do respond as per pH, so that’s why these are called pH-responsive electrodes.

Electrode one is here that is the measuring electrode, and it is a tube made of glass. It consists of thin glass with a glass bulb. It consists of a narrow tube or glass with a glass bulb filled with a potassium chloride chemical with a pH of 7.

It also consists of a silver block of silver chloride attached to a silver element and generates the voltage. It is used to measure the pH of the unknown solution. Then the second electrode of the pH meter is the reference electrode.

The references electrode is also a glass tube that consists of a potassium chloride solution. The reference electrode consists of potassium chloride solution, and it is in contact with the mercury chloride block, which is present at the end of potassium chloride. And this reference electrode is used to provide a stable zero-voltage connection and to complete the circuit.

The pH meter has a flexible arm for easy motion of the electrodes in and out of the solutions. When the pH meter is not in use, the electrode is submerged into three molar potassium chloride solutions to prevent it from drying or direct contact with the environment for a long time. Drying of the glass membrane may permanently damage the electrode.

Also Read: Handling of Laboratory Incident in Pharma

Working of a pH meter

Turn on the pH meter and allow adequate time for it to initialize. Remove the electrode from the storage solution gently. Clean the electrode by rinsing it with deionized water under an empty waste beaker. Once rinsed gently, blot dry with non-abrasive Kim wipes or sure wipes to remove the excess water. Do not rub the electrode as it can damage the sensitive membrane around it before taking any sample measurements.

First, calibrating the pH meter takes three color-coded standard buffer solutions of pH 7.0, 4.01, and 9.21 for calibration. The first buffer used for calibration is always the neutral buffer with a pH of 7.0; the second should always be near the expected sample pH, either 4.01 or 9.21.

Bases should be measured with buffers with a pH of 9.21, while acidic samples should be measured with a pH of 4.01. Place the electrodes in the buffer solution with a pH of 7.0 and allow the pH reading to stabilize at 7. if the H+ ion concentration determines the needed pH

suppose the concentration of H+ ions inside the glass membrane electrode and solution of buffer solution present outside the electrode is the same. In that case, the pH equals 7. once the standard with pH 7.0 is calibrated, rinse the electrode with distilled water and blood dry with Kim wipes.

In the next step, if the sample’s expected pH is acidic, select the buffer solution of pH 4.01, place the electrodes in the buffer with a pH value of 4.01 and press the calibrate button. Allows the pH reading to stabilize at 4.01. if the concentration of H+ ions inside the glass membrane electrode is lower than the buffer solution present outside the electrode, pH will be less than 7.

Once the standard with pH 4.01 is also calibrated, rinse the electrode with distilled water and blood dry with Kim wipes. Similarly, you may skip the previous step if the expected pH of the sample is on the alkaline side and follow this step by using the buffer solution of pH 9.21.

Place the electrodes in the buffer with a pH value of 9.21 and press the calibrate button. Allows the pH reading to stabilize at 9.21 if required pH 10 buffer solution can be used. The concentration of H+ inside the glass membrane electrode is higher than the buffer solution present outside the electrode. Now the pH displayed is more than 7. repeat the rinse process just like the previous steps. Now the pH meter is calibrated and ready to determine the pH of the test sample.

Place the electrodes in the given sample, and then press the measure button to leave the electrodes in your sample until the Reading has stabilized. This will be the exact pH value of your solution. Take the electrodes out, rinse them with distilled water and blot dry with Kim wipes. Immerse the probe in three molar potassium chloride solutions for storage like this. Consult your operation manual for optimal storage practices for your specific pH meter.

Application of pH Meter

  • It is used in the agriculture industry to determine the pH of soil.
  • It’s also used to test the quality of municipal drinking water and swimming pools.
  • It is used to measure the pH value of solutions in numerous chemical and pharmaceutical businesses.
  • The pH metre is also used in the food business, particularly for dairy products such as cheese, curds, and yoghurts.

Advantage of pH meter

  • Provide High Accuracy for extended periods
  • Easy to clean
  • Required less space to install
  • Pocket size pH meter is highly reliable and low cost

The disadvantage of the pH meter

  • Electrodes need to be clean timely to remove deposits. It may cause disturbance in Reading.
  • Careful to handling glass rods properly to avoid breakage

Conclusion:

A pH meter is an electronic equipment that is used to determine the pH of liquids and semi-solids. The features of this indicator were used to determine the acidity or alkalinity of diverse substances precisely. Because it provides reliable readings, the pH meter is more beneficial than other pH indicators used to determine the pH of a liquid or a semi-solid substance.

What is the complete form of pH

pH denotes the potential of hydrogen or the power of hydrogen.

What is pH value or pH scale?

The pH scale is used to determine how acidic or basic an aqueous solution is. Lower pH values indicate more acidic solutions, whereas higher pH values indicate more basic or alkaline solutions. The pH scale is logarithmic and shows the concentration of hydrogen ions in a solution in inverse order. At 25 degrees Celsius, a lower pH indicates a higher concentration of hydrogen ions. A pH less than seven is acidic, and solutions with a pH greater than seven are essential.

What is the equation of pH?

The negative logarithm of hydrogen ion activity is used to calculate pH? formula is pH = -log10(aH+).

What are pH indicators

pH indicators are used to measure pH by using the fact that their colour changes with pH. Visual comparison of the color of a test solution with a standard color chart provides a means to measure pH accurate to the nearest whole number. More precise measurements are possible if the color is measured spectrophotometrically using a colorimeter. The universal indication is a blend of indicators that produces a continuous colour change from around pH 2 to pH 10. Universal indicator paper is comprised of absorbent paper that has had a universal indicator injected into it.

What is the design of the electrode?

The design of the electrodes is significant; they are road-like structures, commonly built of glass, with a bulb at the bottom carrying the sensor. The reference electrode is insensitive to the pH of the solution. It is made up of a metallic conductor that connects to the display, which is made up of a voltmeter that displays voltage in pH units.

What is an ideal requirement of buffer solutions

buffer salts of requisite purity can be obtained from the national institute of standards and technology. Other federal authority’s buffer solutions should be stored in appropriate containers that ensure the stability of the pH through the expiry date and fitted with tight closure.

How many methods to calibrate the pH meter

pH meter calibration shall be performed by two-point calibration, multiple-point calibration, and multiple segment calibration.

The temperature range for calibration or verification is typically done as per the united states pharmacopoeia temperature should be 25 degrees Celsius plus or minus 2°C. While as per British pharmacopoeia and European pharmacopoeia, the temperature should be between 20 °C to 25 °C.

What precautions should be taken while using a test sample sensitive to carbon dioxide in the air?

If the test sample’s pH is sensitive to carbon dioxide in the air, use pure water that has recently been boiled and then stored in a container designed to keep carbon dioxide out.

Can we measure the pH of a gas?

The only way to determine the pH of a gas is to dissolve it in distilled water and measure the result.

What’s the best technique to get rid of air bubbles in a pH probe?

The air probe can become stuck in the reference system’s electrolyte solution, resulting in inconsistent and unstable readings and possibly making it impossible to obtain a reading to remove air bubbles. Shake the probe vigorously in a downward motion to move the air bubbles to the probe’s top end.