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Loss on drying:
- Loss on drying is the loss of mass expressed as per cent.
- Weigh a dry and empty crucible or weighing bottle (Wt empty).
- Place the prescribed quantity of the substance to be examinedabout 1.0g in thiscrucible (Wt sample).
- After drying weight the crucible including the sample (Wt after).
- 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.
- “In a desiccator”: the drying is carried out over diphosphorus pentoxide R at atmospheric pressure and at room temperature;
- “In vacuum”: the drying is carried out over diphosphorus pentoxide R, at a pressure of 1.5 kPa to 2.5 kPa at room temperature;
- “in vacuum within a specified temperature range”: the drying is carried out over diphosphorus pentoxide R, at a pressure of 1.5 kPa to 2.5 kPa within the temperature range prescribed in the monograph;
- “In an oven within a specified temperature range”: the drying is carried out in an oven within the temperature range prescribed in the monograph;
- “Under high vacuum”: the drying is carried out over diphosphorus pentoxide R at a pressure not exceeding 0.1 kPa, at the temperature prescribed in the monograph.
- “Under reduced pressure” means that the drying process is carried out over phosphorus pentoxide, at a pressure not exceeding 0.6 kPa at room temperature, unless otherwise stated.
- “Dry to constant mass” means that the drying process should be continued until the results of two consecutive weighing do not differ by more than 0.5 mg, the second weighing being made after an additional hour of drying under the prescribed conditions
- Calculate: Loss on drying =
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Determination of water by the Karl Fischer :
The titrimetric determination of water by the Karl Fischer method depends on the reaction that takes place quantitatively between water and a reagent consisting of sulfur dioxide and iodine in anhydrous pyridine and usually methanol. The reaction is carried out in a suitable solvent such as methanol or acetic acid.
- Procedure:
- Add about 20 mL of dehydrated methanol R, unless otherwise specified in the monograph, to the titration vessel.
- Titrate methanol with Karl Fischer reagent TS to eliminate residual water in the vessel.
- Quickly transfer the specified quantity of substance, accurately weighed, to the titration vessel.
- Stir for 1 minute and titrate again to the end-point with Karl Fischer reagent TS.
