Loss on drying is the loss of mass expressed as per cent m/m. It is a widely used test method to determine the moisture content of a sample. Where it is measure the amount of water and volatile matters in a sample when the sample is dried under specified conditions (e.g., 60°C, 105°C).
As per USP,
LOD determines the amount of volatile matter of any kind that is driven off under the conditions specified.
Loss on Drying Formula
LOD (%) = (Initial wt. of sample – wt. of sample after drying)/ Initial wt. of sample × 100
LOD Measurement Procedure
Place the prescribed quantity of the substance to be examined in a weighing bottle previously dried under the conditions prescribed for the substance to be examined. Dry the substance to constant mass or for the prescribed time by one of the following procedures. Where the drying temperature is indicated by a single value rather than a range, drying is carried out at the prescribed temperature ± 2 °C.
Sample Quantity for LOD Measurement
As per USP,
- Unless otherwise directed in the individual monograph, conduct the determination of Loss on Drying on a 1g to 2g test specimen. Mix the substance to be tested and, if it is in the form of large particles, reduce the particle size to about 2 mm by crushing before weighing it out.
- Where capsules are to be tested, use a representative sample mixture, excluding the capsule shell, from not fewer than 4 capsules.
- Where tablets are to be tested, use a representative sample mixture from NLT 4 crushed tablets.
References:
- BP - Appendix IX D
- USP - 〈731〉
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