Karl Fischer titration is a titrimetric method commonly used in a pharmaceutical industry for the determination of water content in different substances. Because water content determination is a critical parameter to ensure product quality and to assure the chemical and physical properties of the product.

A German scientist, Karl Fischer discovers this method for quantitative chemical analysis in 1935. Nowadays, The Karl Fischer titrator is a modern automated apparatus that can execute such titrations.

Karl Fischer titration is a titration technique that determines the amount of water contained in a given sample of analyte by using volumetric or coulometric titration. 

 

The selection of the appropriate technique is based on the estimated water content in the sample:

Volumetric Karl Fischer Titration

  • Iodine is added by a burette during titration.
  • Suitable for samples where water is present as a major component: 100 ppm - 100%


Coulometric Karl Fischer Analysis

  • Iodine is generated electrochemically during titration.
  • Suitable for samples where water is present in trace amounts: 1 ppm - 5%


Influence of pH on the Karl Fischer reaction

Since the maximum rate of the Karl Fischer titration is in the pH range 5.5 to 8, pH values less than 4 and greater than 8 should be avoided in practice. With acidic or basic samples, you should adjust the pH value to the ideal range by adding buffering agents (for acids: imidazole, and for bases: salicylic acid).


Karl Fischer Titration Interview Questions and Answers

What is Karl Fischer titration used for?

Karl Fischer titration is widely used for the measurement of water content as a reliable and robust method.

What is KF in pharma?

KF titration method is widely used in pharmaceutical industries as a most reliable and accurate method for water content determination.

What is the principle of Karl Fischer titration?

I2 + SO2 + H2O → 2HI + SO3

The principle of Karl Fischer titration is based on the oxidation reaction between sulphur dioxide and iodine . Water reacts with sulphur dioxide and iodine to form hydrogen iodide and sulphur trioxide. An endpoint is reached when all the water is consumed.

Which reagent is used in Karl Fischer titration?

Karl Fischer reagent consists of iodine, sulfur dioxide and a solvent.

Why methanol is used in KF?

Methanol is used as solvent, which is the most volatile alcohol and is a more polar solvent.

What is the limit of KF factor?

The relative Standard deviation between two average KF factors of water and DST determined consecutively should not be more than 3.0 %

What is KF water factor?

The water equivalence factor F is determined according to the formula 0.1566 x w / v in mgs of H2O per ml of reagent, where W is the sodium tartrate weight in mgs, and V is the reagent volume in ml.

Does Karl Fischer measure bound water?

Yes, karl fischer titration can measure bound water even the tightly “bound” water.

Why pyridine is used in Karl Fischer titration?

As a buffering agent pyridine may used.

Is it require to conduct KF titration in separate room?

Modern KF titrators are automated and closed to atmosphere. There is no need for a separate room.


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