lossondrying

Loss on drying (LOD) is a gravimetric method used to estimate the moisture content or volatile matter in a sample by measuring weight loss after drying under prescribed conditions. The result is expressed as a percentage of the original sample mass.

In a typical procedure, a sample is weighed, dried in a controlled oven or other drying apparatus until a constant mass is reached, and the difference between the initial and final masses is used to calculate the loss. The standard formula is LOD (%) = (initial mass − final mass) / initial mass × 100. The drying conditions—temperature, duration, and atmosphere—depend on the material and the applicable standard or method.

Common conditions include drying at around 105 °C for many pharmaceuticals and foods, with adjustments to 100–110 °C as needed. Alternatives such as vacuum drying or infrared drying may be used for heat-sensitive samples. The choice of method aims to remove water and other readily volatile constituents without altering the sample’s composition.

Applications of loss on drying span pharmaceuticals, chemicals, foods, and soils. It provides a quick QC indicator of moisture content, helps verify batch consistency, and supports compliance with regulatory specifications. It is not a direct measure of water content in all cases, as it captures all volatiles that escape during drying and may be affected by chemical changes in some materials.

Limitations include potential decomposition or volatilization of bound water, sensitivity to sample homogeneity, and the fact that LOD is less precise than dedicated moisture methods such as Karl Fischer titration or azeotropic distillation for water-specific analysis.