Reference: BP / Ph. Eur.
Definition: loss on drying is the loss in weight in % w/w.
The procedure set forth for determination of the amount of volatile matter of any kind that is driven off under the conditions specified
Method – USP:
Weigh a glass stoppered, shallow weighing bottle that has been dried under the same conditions to be employed in the determination for 30 minutes. mix and accurately weigh the substance to be tested, and unless otherwise specified in individual standard procedure., conduct the determination on 1g to 2g. If the test sample is in the form of large crystals, reduce the particle size to about 2mm by quickly crushing. By gentle sidewise shaking, distribute the sample as evenly as practicable depth of about 5mm generally. And not more than 10mm in the case of bulk samples. Place the loaded bottle in the drying chamber, removing the stopper and leaving it also in the drying chamber. Dry the test sample at the temperature and for the time specified in the standard procedure.
The temperature specified in the standard procedure is to be regarded as being within the range of ± 2℃ of the stated figure. after completion, open the chamber and close the bottle with the respective stopper promptly and allow it to cool at room temperature in a desiccator before weighing.
Note:
If the substance melts at a lower temperature than that specified for the determination of loss on drying, maintain the bottle with the contents for 1 to 2 hours at a temperature of 5℃ to 10℃ below the melting temperature, then dried at a specified temperature.
Capsule: Use a portion of the mixed content not less than 4 capsules.
Tablets: Use a powder from not less than 4 tablets ground to a fine powder.
Thermos gravimetric analysis: If the individual standard procedure directs that loss on drying be determined by thermos gravimetric analysis, a sensitive electro balance is to be used.
Drying in Vacuum: When drying in a vacuum over a desiccant is directed in the individual monograph, a vacuum drying pistol, or other suitable vacuum drying apparatus is to be used.
Drying in Desiccator: Where drying in a desiccator is specified in individual standard procedure, ensure that the desiccant is kept fully effective by frequent replacement.
Drying in capillary stoppered bottles: Use a bottle or tube fitted with a stopper having a 225 ± 25µm diameter capillary and maintain the heating chamber at a pressure of 5mm or less of mercury. At the end of the heating period, admit dry air to the heating chamber, remove the bottle with the capillary stopper placed, and allow it to cool in a desiccator before weighing.
Method – BP/Ph. Eur:
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 weight (mass) or 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℃.
Drying in desiccator:
“in a desiccator”: the drying is carried out over diphosphorus pentoxide at atmospheric pressure and at room temperature
Drying in vacuo:
“in vacuo”: the drying is carried out over diphosphorus pentoxide at a pressure of 1.5 kPa to 2.5 kPa at room temperature.
Drying in vacuo within a specified temperature range: The drying is carried out over diphosphorus pentoxide at a pressure of 1.5 kPa to 2.5 kPa within the temperature range prescribed in the monograph.
Drying in the oven:
In an oven within a specified temperature range the drying is carried out in an oven within the temperature range prescribed in the monograph.
Drying under high vacuum:
Under high vacuum, the drying is carried out over diphosphorus pentoxide at a pressure not exceeding 0.1 kPa at a temperature prescribed in the monograph.
Constant weight:
The term ”dried to constant weight” means two consecutive weighings do not differ by more than 0.5mg. The second weight follows an additional period of drying at a prescribed temperature. 1 hour is usually suitable.
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