Loss on Drying Testing in Pharmaceuticals

Loss on drying is described as the loss of weight as percentage of w/w resulting from volatile substances and water of any kind that can be driven off under specified conditions. This test is done on a mixture of substances. If substance to be tested is in the form of large particles then the sizes must be reduced by rapid crushing to a powder. The test is to determine the water content and volatile substance in a sample is exposed to heat. Loss on drying is a technique that has been used by many pharmaceuticals. There are different methods of carrying out this test an d the technician chooses the most appropriate one depending on the substance being tested.

To carry out the test, do the following:

· Weigh a shallow weighing bottle that has been dried under the same conditions that will be employed in the determination.

· Transfer to the dry bottle the quantity of the sample specified in the individual monograph.

· Cover the bottle and accurately weigh it and the contents.

· Distribute the sample evenly by gentle side wise shaking to a depth not exceeding 10 mm.

· Dry the substance by placing the bottle in the drying chamber

· Remove the stopper and leave it in the chamber.

· Dry the sample to constant weight.

· Open the drying chamber and close the bottle promptly and let it to cool to room temperature.

· Weigh the bottle and its contents.

The temperature at which you should expose the substance to be tested is always specified and must not be exceeded lest you get the wrong results. Every substance has its specific heat level.

Loss on drying testing in pharmaceuticals is a technique of removing water and other volatile impurities from a sample of well-mixed substance. the amount of heat applied on the substance is dependent on time and temperature.

Total moisture content of pharmaceutical products can contain both bound and free water.

Where there are impurities present then loss on drying level will be higher as compared to water content.

Sometimes loss on drying level may be far lower compared to the content of water since some water molecules may not be removed heating as in other methods of determining loss on drying does. To calculate the percentage loss on drying, below is the method.

Percentage LOD = Percentage Water content – Percentage molecules of water in the API

One must know the type of substance being used prescription must be exactly known so as to determine how the experiment is carried out. For hydrate substance, anhydrous content equivalent weight should be calculated before being exposed to heating. In case any moisture is specified on the certificate the pharmacy before the substance is used in loss on drying experiment.


Loss on drying has been used in many pharmaceutical companies to determine the concentration of drugs. These experiments are used for testing to determine moisture present substances also. This experiment requires a lot of care and keenness for true results to be found. Weight must be measured with non-faulty devices to ensure the wait is exact. During heating, it must be done to completion to make sure to water is left.