Karl Fischer Testing

karl fischer testing
Karl Fischer Method of Moisture Detection

At Applied Technical Services we maintain a state of the art Karl Fischer unit capable of volumetric and coulometric titration which offers a detection limit of 5ppm ±5 µg. Our system also utilizes a specialized oven attachment which allows analysis of moisture in solid samples by vaporization of the moisture. Our Karl Fischer unit is able to provide moisture measurements in terms of % moisture, parts per million (PPM), and micrograms (µg) of water.

Karl Fischer (KF) Titration is a technique for the determination of moisture content. It is a process based on the reaction of iodine with water. The KF method is one of the few techniques that will measure water content and not be affected by other volatiles. With our KF titration unit both free and bound water can be determined, for example surface water on crystals or the water contained inside them. The method works over a wide concentration range from 5 ppm up to 100% and supplies reproducible and accurate results. Our unit can effectively test numerous types of solid or liquid samples. Sample size can vary and is typically between 0.5-5 grams depending on the water content within the sample. There are two methods used to perform the Karl Fischer titration test, Volumetric and coulometric.

Volumetric titration is used for moisture content above the 1-2% range. In this method samples are injected directly into an air tight titration cell containing a solvent and dissolved before the titration begins. Through the use of an automatic buret, reagent is added and reacts with the water to return the conductivity to the starting point. The amount of water/moisture in the sample is calculated based on the amount of reagent need to reach this point. It has a range of moisture content from 100 parts per million to 100%.

For coulometric titration the reagent and solvent are combined in the titration cell. When a sample is introduced into the titration cell and dissolved, reagent is released by the induction of an electrical current. The moisture is determined by the amount of current required to consume the water. The advantage of the coulometric KF method is the capability to accurately measure small amounts of moisture. Sensitivity of our instrument is as low as 0.1 micro-gram (µg) of water. This method is normally used for moisture content below 1 % or for samples where the moisture is less than 200 micrograms.

The addition of a specialized oven allows analysis of moisture in solid samples, or unique liquid samples by vaporization of the moisture. For a sample to work by direct injection it needs to be dissolvable in a solvent compatible with the KF Reagents. Substances that release their water slowly or at high temperatures (e.g., plastics or inorganic salts) are not suitable for a direct Karl Fischer titration. For these samples we are able to determine moisture using the oven attachment.

The sample is weighed into its own sample vial and hermetically sealed, which minimizes contamination and carry over effects. Using PTFE-covered septa prevents any moisture uptake from ambient air. The vial is placed in the oven chamber and heated, a carrier gas transfers the released water to the titration cell, where it is then determined by KF titration. Depending on the sample’s water content, the subsequent KF water determination can be carried out volumetrically or, for trace amounts, coulometrically. Since only the water enters the KF cell and the sample itself does not come into contact with the KF reagent, unwanted side reactions and matrix effects are eliminated. You can determine the water content of solids (powders or granules), liquids of different viscosities, plus pastes and fats.

These methods are widely used in the areas of transformer oil monitoring, crude and lube oil analysis, polymer analysis, and many applications in the solvent, pharmaceutical and chemicals industries.

Example applications, moisture content of:

  • Petrochemicals, including fuels, oils, crudes, hydraulic fluids and lubricants
  • Polymers, including pellets, polymer/solvent mixtures, raw materials and precursors
  • Pharmaceuticals, including powders, liquids, tablets/pills and lyophilized samples
  • Cosmetics, including makeup, soaps, and toothpaste
  • Chemical Applications, including solvents, salts, organic matter, and metals
  • Foods, including liquids, formula, mixes, and others
Solvents Finished Products Industrial Products
Acetic acid Aftershave lotion Freon
Acetonitrile Almond oil Gasoline
Benzene Aperitif Insulating Oil
Chloroform Butter Metal oxides
Cresols Coffee cream Mineral oil
Cyclohexane Cognac Nitrogen
Dioxane Cough syrup Petroleum
Ethanol Epoxy Plastic films
Furan Formula Plastic granules
Glycerol Lotion Salicylic acid
Chexane Margarine Salts
Isopropanol Mascara Silicone oil
Liquid paraffin Mustard Sulphuric acide
Nitrobenzene Paint Transformer Oil
Octanol Sun screen
Petroleum ether Vinegar
Pyridine
Tetrahydrofuran
Toluene
Vinyl ether
Xylene

The ATS team of organic chemists are very skilled at assessing the situation and determining the appropriate equipment and test methods to utilize in order to test for suspected or known contaminants.

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