Determination of Loss on Drying (LOD)

Title: Determination of Loss on Drying

 

1.      Objective: To determine the Loss on drying in the sample.

 

2. Principle:

• Loss on drying is the loss in weight in % w/w resulting from water and volatile matter of any kind that can be driven off under specified conditions.
• Thermogravimetry is a technique in which the weight of a sample is recorded as a function of temperature according to a controlled temperature programme.

        

4. Procedure:

The test is carried out on a well-mixed sample of the substance. If the substance is in the form of large crystals, reduce the size by rapid crushing to a powder.

Where the drying temperature is indicated by a single value, dry at the prescribed temperature ± 2°C.

Unless otherwise specified in the individual monograph, use Method A.

 

• Method A:

Weigh a glass-stoppered, shallow weighing bottle that has been dried under the same conditions to be employed in the determination. Transfer to the bottle the quantity of the sample specified in the individual monograph, cover it and accurately weigh the bottle and the contents. Distribute the sample as evenly as practicable by gentle sidewise shaking to a depth not exceeding 10 mm. Place the loaded bottle in the drying chamber (oven or desiccator) as directed in the monograph, remove the stopper and leave it also in the chamber. Dry the sample to constant weight or for the specified time and at the temperature indicated in the monograph. After drying is completed, open the drying chamber, close the bottle promptly and allow it to cool to room temperature (where applicable) in a desiccator before weighing. Weigh the bottle and the contents.

1. “In a desiccator”: dry over phosphorous pentoxide at a atmospheric pressure and at room temperature;

NOTE: Care must be taken to keep the desiccant fully effective by frequent replacement.

1. “ in vacuo” dry over phosphorous pentoxide at a pressure of 1.5 kPa to 2.5 kPa  at room temperature;
2. “in vacuo” with a specified temperature range”:dry over phosphorous pentoxide at a pressure of 1.5 kPa to 2.5 kPa with temperature range given in the monograph;
3. in an oven in a specified temperature range”:dry in an oven within the range given in the monograph;
4. “under high vacuum ”: dry over phosphorous pentoxide at a pressure of 0.1.5 kPa  at the given in the monograph;

 

Calculation:

Weight of empty LOD Bottle:  W₁

Weight of LOD Bottle + sample: W₂

Weight of sample:  W₃ (W₂ – W₁)

Weight of LOD Bottle + sample (After dying): W₄

Weight Loss: W₅ (W₂ – W₄)

 

% Loss on drying =    W₅   x 100_____

W₃

 

• Method B:

Thermogravimetry: Thermogravimetry is a technique in which the weight of a sample is recorded as a function of temperature according to a controlled temperature programme.

 

• Apparatus:

A thermobalance consisting of a device for heating or cooling the substance being examined according to a given temperature programme, a sample holder in a controlled atmosphere, an electrobalance and a recorder. The instrument may be coupled to a device permitting the analysis of volatile products.

• Temperature verification: Check the temperature scale using nickel or other suitable material according to the manufacturer’s instruction.
• Calibration of the Electrobalance: Place a suitable quantity of calcium oxalate monohydrate RSin the sample holder and record the weight. Set the heating rate according to the manufacturer’s instructions and start the temperature programme. Record the thermogravimetric curve as a graph with temperature on the abscissa, increasing from left to right, and weight on the ordinate, increasing upwards. Stop the rise in temperature at 230°. Measure the distance on the graph between the initial and final weight-temperature plateaux that corresponds to the loss of weight. The declared loss of weight for calcium oxalate monohydrate RS is stated on the label.

NOTE: If the apparatus is in frequent use, carry out temperature verification and calibration regularly. Otherwise, carry out such checks before each measurement.

• Procedure:

Apply the same procedure to the substance being examined, using the conditions prescribed in the monograph. Calculate the loss of weight of the substance being examined from the distance measured on the graph obtained and express as a percentage w/w of the substance taken.

The actual procedure and the calculations to be employed are dependent on the particular instrument used. Consult the manufacture’s literature and/or the thermal analysis literature for the most appropriate technique for a given instrument. In any event, it is imperative to keep in mind the limitations of solid solution formation, insolubility in the melt, polymorphism and decomposition during the analysis.

 

 

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