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Loss on Drying and Moisture Content

You will find here the differences and similarities between Loss on drying and water (moisture) content, these calculations and testing methods.

This is one of the most frequently asked questions in interviews and also creates confusion in many people’s mind about the differences.

What is LOD and Moisture content?

LOD: The Loss on Drying Test is designed to measure the amount of water and volatile matters in a sample when the sample is dried under specified conditions.

Moisture content: Water content or moisture content is the quantity of water contained in a material, such raw materials, API and blend.

Water content or moisture content is the quantity of water contained in a material, such raw materials, API and blend.
The Loss on Drying Test is designed to measure the amount of water and volatile matters in a sample when the sample is dried under specified conditions.
Karl Fischer Titration and Loss on Drying (LOD) are both methods for determining moisture content in a product.

Karl Fischer Titration is a method Karl fisher titratormeasures only the water content (i.e. it’s water-specific) in a product sample.
The results does not contain other volatile matter except the water.

Where as Loss on Drying, measures the total change in weight of a material as a result of drying. It is an unspecific analytical technique removing not only water but all other volatile impurities like alcohol and fat also evaporates with water from a sample.Moisture analyser

Therefore, the LOD method measures both the water and volatile impurities.

Working principles of both methods.

Karl Fischer titration is a chemical method. It involves adding a reagent to the sample to cause a reaction that converts the water in a product to a non-conductive chemical.

Loss on Drying compares the weight of a product before and after it is dried. This difference in weight is taken as the percentage of moisture in the product.

How to calculate LOD and Moisture content:

 % LOSS OF DRYING = [MASS OF WATER IN SAMPLE (KG)/ TOTAL MASS OF WET SAMPLE(KG)] * 100

% MOISTURE CONTENT = [MASS OF WATER IN SAMPLE(KG)/ MASS OF DRY SAMPLE(KG)]  *100

  • LOD or total moisture content of Pharmaceutical products can include both bound (e.g. water of hydration) & free moisture (water).
  • In cases there are additional traces of other volatile impurities present, like alcohol; LOD may be higher than water content.
  • In other cases, LOD may be lower than water content, as bound crystal water may not be removed by heating.”

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