pH METER PRINCIPLE:

pH meter is a scientific instrument which measures the hydrogen-ion activity in solutions, indicating its acidity or basicity(alkalinity) expressed as pH. ph meter principle is pH value is the concentration of hydrogen ions in the solution e.g. It is the negative logarithm of an Hydrogen ion. pH range of solutions varies between 1 to 14, where 1 is the highest in acidic nature.

The pH meter measures the difference in electrical potential between a pH electrode and the reference electrode, that is why the pH meter is sometimes referred to as a “potentiometric pH meter”.

Calibration of pH Meter:

Calibration of pH meter is a very important function which should be performed every day before performing any test on the meter.

Preparation of Standard Buffer

Buffer Solution pH 4.00 (200C) Transfer the content of buffer capsule or tablet pH 4.00 into a 100 ml volumetric flask. Dissolve in about 80 ml of purified water, make up the volume to 100 ml with purified water & mix.

Buffer Solution pH 7.00 (200C) Transfer the content of buffer capsule or tablet pH 7.00 into a 100 ml volumetric flask. Dissolve in about 80 ml of purified water, make up the volume to 100 ml with purified water & mix.

Buffer Solution pH 9.20 (200C) Transfer the content of buffer capsule or tablet pH 9.2 into a 100 ml volumetric flask. Dissolve in about 80 ml of purified water, make up the volume to 100 ml with purified water & mix.

Calibration of pH meter:

Operate the pH meter and electrode system according to the manufacturer’s instructions or according to the applicable SOPs. All measurements should be made at the same temperature of 20° to 25°. The apparatus is calibrated with the buffer solution of potassium hydrogen phthalate (primary standard) (buffer pH 4.0) and one other buffer solution of different pH, preferably buffer pH 9.2. The measured pH of a third buffer pH 7.0 must not differ by more than 0.05.

Calibration Procedure:

  • The instrument is calibrated to pH 4, 7 or 9.2 but remembers to calibrate pH 7 first.
  • Dip the electrode in standard Buffer Solution of 7.00 pH value. 
  • Measure the temperature of the solution and place the temperature knob accordingly.
  • Bring the Function Switch of pH Mode.
  • Adjust the “Calibrate” control so that the display reads 7.00
  • Now again turn the Function Switch into Standby Mode.
  • Remove the electrode from 7 pH buffer solution and wash it with distilled water, soak & dry it.
  • Put the electrode in 4 pH buffer solution.
  • Bring the Function Switch in pH Mode and Adjust the “Slope %” (Right side of the instrument) so that the display reads 4.00.
  • Remove the electrode from 4 pH buffer solution and wash it with distilled water.
  • Always keep the Function Switch at standby Mode after measuring the pH value.

Procedure and operation of pH Meter

  • Ensure the temperature of Liquid being examined to 200-250C.
  • Immerse the glass electrode in the liquid to be examined.
  • Turn off the knobs to pH Checking & note.
  • When measuring the pH above 10, ensure that the electrode is suitable for use under alkaline conditions & apply any correction that is necessary.
  • Record the pH of the solution used to standardise the meter and electrodes at the end of a set of measurements. If the difference between this reading and the original value is greater than 0.05, the set of measurements must be repeated.

Types of pH meters

  1. Traditional pH Meter
  2. pen-like devices
  3. pH strips
  4. Holographic pH sensors
  5. Solid-state electrodes pH Meter
  6. Voltmeter display device.

SUMMARY:

pH meter is an essential part of the chemical industry, Food Industry, Pharmaceutical Industry and Agriculture sector. It allows us to know the nature of the solvent and therefore provides insights to take further actions accordingly. If a product has low pH then the manufacturer can raise its pH with some alkali solutions. However, pH meter looks a very simple scientific instrument but it’s functionality put it at the top position of Chemio-physics instruments. pH meter is a physics instrument but it’s working is chemistry oriented.