Learn everything about Karl Fischer titration for water determination in pharmaceuticals, food, and cosmetics. Explore its principle, procedure, reagents, reactions, applications, case studies, and FAQs.
Karl Fischer (KF) Titration is widely used for water determination in various industries such as the pharmaceutical industry, food industry and cosmetic industries. It also plays a vital role during drug development. In this article, I will discuss principles, applications, procedure, KF reagent, KF reaction, sample size, effect of pH, case studies and FAQs. After reading this article, all your doubts will be cleared, and your knowledge will increase to the next level.
The Karl Fischer titration is widely used for a variety of products for water determination in various industries. The principle of KF titration is based on the Bunsen reaction between iodine and sulfur dioxide in an aqueous medium. Karl Fischer modified this reaction in a non-aqueous system containing an excess of sulfur dioxide. He used methanol as a solvent and pyridine as a buffering agent.
ROH + SO2 +R’N → [R’NSH]SO3R + H2O +I2 + 2R’N → 2[R’NH]I + [R’NH]SO4R
Related: What is Karl Fischer Coulometric Titration: Learn in 5 Minutes
The rate of reaction depends upon the pH value of the solvent or working medium. When pH is between 5 to 10, then titration proceeds normally. However, when the pH is lower than 5 the titration speed is very slow. On the other hand, when pH is higher than 8, then the titration rate is very fast, but only due to interfering esterification, which produces water, resulting in a vanishing endpoint. Thus, the optimal pH range for Karl Fischer titration is between 5 to 8. The highly acidic or highly basic samples need to be buffered to bring the overall pH in that range.
Boost your pharma career with PharmaGuru’s expert-led online courses.: Online Pharma Course (Training)
The equipment used in the Karl-Fischer titration consists of a titration vessel, a burette, a Karl-Fischer titration reagent, and the sample being tested. The titration vessel is filled with the sample, whereas the burette is filled with Karl-Fischer reagent. The burette is then attached to the titration vessel and the Karl-Fischer reagent is allowed to flow into the sample. The amount of water in the sample is determined by measuring the amount of Karl-Fischer titration reagent required to fully titrate the sample.
The KF reagent contains iodine, sulfur dioxide, a base (imidazole) and a solvent
In the KF titration vessel, about 50 ml of methanol is taken and is neutralised with Karl Fischer reagents. Then the sample is added as per the respective method and titration is started. The KF instrument automatically detects the endpoint and gives the result.
KF titration is used in the following industries for the determination of water:
The following are the advantages of KF titration for water determination:
It works well between pH 5 to 8
The following are the differences between KF and LOD:
| LOD | KF |
| It is based on the physical mass determination after the evaporation of organic solvents and water | It is not a specific method since it gives combine value of water and solvents |
| It is based on the chemical reaction between KF and the water molecules of the sample | It gives only water value |
| Bonded water can not be determined by LOD | Both bonded/crystalline and free water can be determined by KF |
| It is a specific method since it gives only value of water | It is an accurate method |
| It is accurate method | It is more accurate than LOD |
The KF titration is a powerful technique for the determination of water in the various industries, and it gives fast, accurate and reliable results. I hope this post has cleared all your doubts and increased your knowledge to the next level. Write your opinion and suggestions in the comment section.
You May Like
In the KF titration, in the titration vessel, about 50 ml of methanol is taken and it is neutralised with Karl Fischer reagents. Then sample is added as per the respective method and titrated with the KF reagent. The KF instrument automatically detects the endpoint and gives the result.
It gives fast, accurate and reliable results. Secondly, it does not need any special skill. That is why KF is used in water determination.
In the KF titration, in the titration vessel, about 50 ml of methanol is taken and it is neutralised with Karl Fischer reagents. Then sample is added as per the respective method and titrated with KF reagent. The KF instrument automatically detects the endpoint and gives the result.
In KF instrument double platinum electrode is used for electrochemical indication of the end-point.
n the KF titration, in the titration vessel about 50 ml of methanol is taken and it is neutralised with Karl Fischer reagents. Then sample is added as per the respective method and titrated with the KF reagent. KF reagent contains iodine, sulfur dioxide, a base (imidazole) and solvent.
The alcohol reacts with Sulfur Dioxide and base to form an intermediate alkyl sulfite salt, which is then oxidised by iodine to an alkyl sulfate salt. This oxidation reaction consumes water. Once all of the water present in the sample is consumed, the presence of excess iodine is detected voltametrically by the titrator’s indicator electrode. That signals the endpoint of the titration.
ROH + SO2 +R’N → [R’NSH]SO3R + H2O +I2 + 2R’N → 2[R’NH]I + [R’NH]SO4R
The KF method is selective for water, and it only gives the water value of the same, whereas the LOD method is not selective and it gives a combined value of water and organic solvent.
Quick Links