This is a test used to determine the amount of volatile substances (mainly water) present in a sample by measuring its weight loss after drying. It is commonly used in pharmaceuticals, food, chemicals, and other industries to check the moisture content in raw materials and finished products.
Principle:
A sample is heated under controlled conditions (specific temperature and time), and the weight loss is measured. This loss represents moisture and other volatile substances that evaporate under those conditions.
Detailed Procedures & Instrumentation of LOD :
1. Traditional Oven Drying Method (Gravimetric Method) :
This is the most commonly used method in pharmaceutical and chemical industries, following pharmacopeial guidelines (USP, BP, IP).
Procedure
Sample Preparation: Weigh a clean, dry crucible or weighing dish.
Weighing: Accurately weigh the sample (typically 1–2 g) and place it in the dish.
Drying:
Place the dish in a hot air oven set at 105°C – 110°C (or as specified).Dry for 1–2 hours (or per pharmacopeial specifications).
Cooling & Weighing: Transfer the dish to a desiccator to cool (to avoid moisture absorption from the air).
Weigh the sample again.
Measures : Moisture + Volatiles
2. Infrared Moisture Balance Method (Rapid Method) :
This method is used for faster results compared to the oven-drying method.
Procedure:
Weigh the sample on the infrared moisture balance.
Set the heating temperature (varies based on the sample type, typically 100–120°C).Start the drying process; the instrument continuously measures weight loss. Once the sample reaches a constant weight, the moisture content is displayed automatically.
Measures : Moisture + Volatiles
3. Karl Fischer Titration (For Water Content Only):
This method is used when only water content (not other volatile substances) needs to be measured. It is commonly used for pharmaceuticals, chemicals, and food products.
Procedure:
The sample is dissolved in a suitable solvent (e.g., methanol).Karl Fischer reagent (containing iodine and sulfur dioxide) is titrated against the sample. The reaction stops when all water is consumed, and the water content is calculated.
Measures : Only water
Related Topics:
| Partition Coefficient | Dissociation Constants | Bulk Density |
| KF Titration | LOD vs Water Content | Water for Analysis |
Resource Person: Susmita