Loss on Drying Constant Weight?

[Ajay26 (Ajay Bombale)]

In case of LOD testing constant weighing is necessary or not?
USP talk about monograph only for drying time but constant weighing clarity not available.

[sunilrbudhkar]

Please refer ‘Loss of drying’ test under the general chapters and notices in the USP which are separately given apart from the monographs of raw materials and drug products.

[Ankur (Ankur Choudhary)]

@Ajay26

constant weighing is necessary or not

Constant weight is necessary to confirm that LOD bottle is cooled to room temperature. The hot LOD bottle didn’t show constant temperature.

[jayaram (Jaya)]

Constant weight is required, to ensure that the sample is completely dried at specified temperature. After drying time completed, check the LOD and again dry the same sample for some time. check the weights difference between the two intervals. The variation should be less than 10.0% of the specification.
Then only we can say that the product is completely dried.

[sunilrbudhkar]

According to USP/NF if the monograph of raw material specifies Loss on drying (at specified temp) is to be performed to constant weight, then it means that the difference between weights of sample of two successive drying must not be more than 0.5 mg per gm of sample. This indicates that even after drying the same sample for a second time there is no further loss in weight. Hence the drying at specified temp was done adequately till constant weight is obtained.
The requirement of drying the sample to constant weight in the LOD test is specified in some of the monographs of raw materials as per USP/NF. It is not a requirement for all the materials specified in USP/NF monographs. For example in the monograph of Magnesium stearate as per USP specifies under LOD test that “Dry at 105 deg C to constant weight”.

Please refer general chapter of test procedure <731> of Loss on drying. It says that When “dry to constant weight” is specified in a monograph, drying shall be continued until two consecutive weighings do not differ by more than 0.50 mg/g of specimen taken, where the second weighing follows an additional hour of drying. Upon opening the chamber, reapply the same stopper to the bottle, and allow it to come to room temperature in a desiccator before weighing accurately.