á731ñLOSS ON DRYING
The procedure set forth in this chapter determines the amount of volatile matter of any kind that is driven off under the conditions specified.For substances appearing to contain water as the only volatile constituent,the procedure given in the chapter,Water Determination á921ñ,is appropriate,and is specified in the individual monograph.
Mix and accurately weigh the substance to be tested,and,unless otherwise directed in the individual monograph,conduct the determination on 1to 2g.If the test specimen is in the form of large crystals,reduce the particle size to about 2mm by quickly crushing.Tare a glass-stoppered,shallow weighing bottle that has been dried for 30minutes under the same conditions to be employed in the determination.Put the test specimen in the bottle,replace the cover,and accurately weigh the bottle and the contents.By gentle,sidewise shaking,distribute the test specimen as evenly as practicable to a depth of about 5mm generally,and not more than 10mm in the case of bulky materials.Place the loaded bottle in the drying chamber,removing the stopper and leaving it also in the chamber.Dry the test specimen at the temperature and for the time specified in the monograph.[NOTEThe temperature specified in the monograph is to be regarded as being within the range of ±2of the stated figure.]Upon opening the chamber,close the bottle promptly,and allow it to come to room temperature in a desiccator before weighing.
If the substance melts at a lower temperature than that specified for the determination of Loss on drying,maintain the bottle with its contents for 1to 2hours at a temperature 5to 10below the melting temperature,then dry at the specified temperature.
Where the specimen under test is Capsules,use a portion of the mixed contents of not fewer than 4capsules.
Where the specimen under test is Tablets,use powder from not fewer than 4tablets ground to a fine powder.
Where the individual monograph directs that loss on drying be determined by thermogravimetric analysis,a sensitive electrobalance is to be used.
Where drying in vacuum over a desiccant is directed in the individual monograph,a vacuum desiccator or a vacuum drying pistol,or other suitable vacuum drying apparatus,is to be used.
Where drying in a desiccator is specified,exercise particular care to ensure that the desiccant is kept fully effective by frequent replacement.
Where drying in a capillary-stoppered bottle*in vacuum is directed in the individual monograph,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,and with the capillary stopper still in place allow it to cool in a desiccator before weighing.
* Available as an antibiotic moisture content flaskfrom Kontes,1022Spruce St.,Vineland,NJ08360-2841.