Karl Fischer Titration: Procedure, Advantages, and Applications

Karl Fischer titration is a titration method that determines the quantity of water present in a given analyte using volumetric or coulometric titration.

• Karl Fischer, a German scientist, invented this method for quantitative chemical analysis in 1935.
• To perform such titrations, specialist titrators (known as Karl Fischer titrators) are presently available. 
• Titration is the process of determining the volume of a substance by adding another measured substance with which the desired constituent reacts in a definite known proportion.
• Titration is an important tool in analytical chemistry.

Key Terms: Titration, Karl Fischer Titration, Acid-base Titration, Redox Titration, Oxidation-reduction, Anode, Cathode, KF reagent, Spectroscopy

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Types of Titration

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Titration can be done by a long glass tube with a scale called a burette.

• It can also be done by using a titration cell.
• There are two kinds of solutions in the process of titration a titrant and an analyte.
• The solution of a known concentration is called a titrant, whereas the solution which is going to be studied is called an analyte
• Titration can be done through two methods: the volumetric method and the colourimetric method.
• In the volumetric method, the titrant is directly added to the sample by a burette.
• In the coulometric method, the titrant is generated electrochemically in the titration cell.

In analytical chemistry, there are three types of titration. They are

• Simple Titration
• Back Titration
• Double titration.

Simple titration is of different types

• Acid-base Titration
• Redox Titration
• Precipitation Titration
• Complexometric Titration.

A redox titration is a titration in which the analyte and the titrant react through an oxidation-reduction reaction. Karl Fischer titration is a redox type of titration.

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Karl Fischer Titration (KF Titration)

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Karl Fischer Titration is an important analytical method to determine the volume of a chemical constituent in analytical chemistry.

• In this titration method, either volumetric titration or coulometric titration is used to determine the quality of water in a given sample.
• Karl Fischer Titration is an oxidation-reduction type of titration.

Principle of Karl Fischer Titration

It is based on the oxidation reaction between sulphur dioxide (SO₂) and iodine (I₂).

• In the process, the given sample of water reacts with sulphur dioxide and iodine to form hydrogen iodide (HI) and sulphur trioxide (SO₂).
• The reaction goes on till the entire quantity of water gets utilised.
• This is the endpoint of the reaction.

The Bunsen equation for the reaction is as follows:

2H₂O + SO₂ + I₂ → 2HI + SO₃

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Apparatus for Karl Fischer Titration

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The apparatus used for Karl Fischer Titration is as follows

• Drying tube
• Analytical electrode solution
• Detection electrode
• Sample injection cap
• Drain cook
• Anode chamber
• Cathode chamber
• Rotor
• KF reagent

KF Reagent Constituents

The following are the KF reagent constituents

• Iodine
• Solvent (methanol)
• Sulphur dioxide
• Buffer (Imidazole)

Preparation of the KF Reagent

• Step 1: A solution is prepared by adding 670 mL of methanol to 170 mL of pyridine (C₅H₅N)
• Step 2: Add 125 g of iodine to the above solution and cool the solution.
• Step 3:  Add 100 mL solution to a 250 mL graduated cylinder. Keep the solution in an ice bath.
• Step 4: Pass dry sulphur dioxide into the cylinder till its volume reaches 200 mL.

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Karl Fischer Titration Procedure

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The Karl Fischer titration experiment can be carried out in two ways. They are as follows:

Volumetric Determination

Volumetric determination is done by using a burette in the laboratory.

• The given water sample is dissolved in KF methanol.
• Later iodine is added to the KF reagent. 
• One mole of iodine is consumed for one mole of water.
• The titration reaction proceeds until the total utilization of the water sample.
• The endpoint is determined by the potentiometric method.

Coulometric Determination

Here a titration cell with two compartments is used.

• One compartment consists of the anode solution and an analyte.
• The anode solution consists of alcohol, sulphur dioxide and iodine.
• The second compartment is immersed with a cathode electrode.
• The two compartments are separated by an ion-permeable membrane.
• Oxidation of sulphur dioxide is done by iodine.
• One mole of iodine is consumed for each mole of water.
• Two moles of electrons are consumed for each mole of water. 
• Here, the endpoint is determined by the potentiometric titration method.
• The iodine needed for the KF reaction is obtained by anodic oxidation of iodide from the solution.

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Advantages of Karl Fischer Titration

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The following are the advantages of Karl Fischer Titration

• It shows extreme accuracy as it is based on chemical reactions in KF titration.
• It does not detect the loss of volatile substances in the process.
• It has a wide range of determination of water quality and quality.
• KF titration can be used for smaller samples also.
• It is a quick method to determine the quality of water in different commercial substances.
• It can be equally employed to determine water quality in solids, liquids and gases.
• The coulometric titrator helps in detecting free water, dissolved water, and emulsified water.
• It is an automation technique.
• The spectrophotometer can be used to detect the endpoint by using coloured samples.
• It is done through UV-ViS spectroscopy (UV – ultraviolet and VIS – visible light).

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Limitations of Karl Fischer Titration

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The following are the disadvantages of Karl Fischer Titration

• Wastage of solvent due to manual volumetric KF titration.
• The margin of error is more in volumetric KF titration.
• Coulometric KF titration is applicable only to smaller samples.
• Water in chocolates cannot be determined without dissolving the chocolate.
• Water in some organic chemicals like aldehydes, ketones, etc. is not suitable for this method. 
• KF is unsuitable for the solvents like LiCl (Lithium Chloride).

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Applications of Karl Fischer Titration

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The following are the applications of Karl Fischer Titration

• It is used to know the quality of water, used for different purposes.
• It is used in food, oil, pharmaceutical and semiconductor industries.
• In the food industry, it is used to determine water content in chips, cocoa powder, flour, fruit juices, honey, noodles, etc.
• In the cosmetic industry, it is used to know water content in creams, lipstick, shampoos, toothpaste, etc.
• In the pharmaceutical industry, it is used to know water content and quality in ointments and pills.
• In the petrochemical industry, it is used to determine water content in gasoline, kerosene, and petroleum.
• It is also used to know water content in silk, wool, wood, paper, cement, plastics, oils, gases, etc.

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Things to Remember

• Titration is the process of determining the volume of a substance by adding another measured substance with which the desired constituent reacts in a definite known proportion.
• There are two kinds of solutions in the process of titration a titrant and an analyte.
• The different types of titration are Simple Titration, Back Titration, and Double titration.
• Simple titration is of different types: Acid-base Titration, Redox Titration, Precipitation Titration, and Complexometric Titration.
• In redox, titration is the titration of an analyte and a titrant reacts through an oxidation-reduction reaction.
• Karl Fischer titration is a redox type of titration.
• Karl Fischer titration is a titration method that uses volumetric or coulometric titration to determine the amount of water contained in a given analyte.
• Karl Fisher invented a titrator to make an accurate analysis of water in any sample.
• The solution of a known concentration is called a titrant, whereas the solution which is going to be studied is called an analyte.