#### pH Meter

A pH meter is a scientific instrument in pharmaceutical industry that measures the hydrogen-ion activity in a solution, indicating the degree of acidity or alkalinity and expressed as pH. It is measured on a scale of 0 to 14.

#### pH Meter Application in Pharma

pH meter is an important instrument for pH dependent pharmaceutical products. The application of pH meter in pharmaceuticals are mentioned below -

• To identify the pH of a RLD/RS
• To develop a pH dependent product like cream, syrup, eye drops, injection etc.
• To routine check during production of pH dependent product
• To check dissolution media at different pH

#### Principle of pH Meter

A pH meter will be made up of a probe, which itself is made up of two electrodes. This probe passes electrical signals to a meter which displays the reading in pH units. The glass probe has two electrodes because one is a glass sensor electrode and the other is a reference electrode. Some pH meters do have two separate probes in which case one would be the sensor electrode and the other the reference point.

Both electrodes are hollow bulbs containing a potassium chloride solution with a silver chloride wire suspended into it. The glass sensing electrode has a bulb made up of a very special glass coated with silica and metal salts. This glass sensing electrode measures the pH as the concentration of hydrogen ions surrounding the tip of the thin walled glass bulb.

#### Calibration of pH Meter

pH meter calibration is a necessary step of using a pH meter because of how the electrode changes over time.

A 2 or 3 point calibration, using 2 to 3 different buffer solutions is usually sufficient for initial calibration as the meters electronic logic will calculate the pH values in between.

#### FAQS

What is the range of pH meter?

• The range of pH meter fall from 0 to 14

What is pH full form?

• Full form of pH is potential of hydrogen

What does pH stand for?

• pH stand for potential of hydrogen

Which equation is relates to pKa & pH?

• The Henderson-Hasselbalch equation relates pKa and pH.

How do I calculate pH?

• pH = −log [H+]

What is the principle of pH?

• The basic principle of the pH meter is to measure the concentration of hydrogen ions in a solution. Where acids dissolve in water forming positively charged hydrogen ions (H+). The greater this concentration of hydrogen ions, the stronger the acid is.

What is the basic buffer?

• The buffer is prepared by mixing a weak base and its salt with strong acid.

What is the pH of pure water?

• 7.0

Does pH can equal to pKa?

• Yes, it can be. When the pH is equal to the pKa value, the proportion of the conjugate base and conjugate acid are equal to each other.

#### Example of pH Calculation

Find pH for a solution of 0.225 M NaNO2 and 1.0 M HNO2. The pKa value 3.14.

pH = pka + log ([A-]/[HA])

pH = pKa + log([NO2-]/[HNO2])

pH = 3.14 + log(1/0.225)

pH = 3.14 + 0.648 = 3.788