Loss on Drying (LOD)

About Loss on Drying

Source: USP General Chapter 〈731〉 Loss on Drying

What is Loss on Drying (LOD) and Determination of Loss on Drying (LOD)

LOD: It is an analytical method for removing all volatile impurities like alcohol etc. from a test sample. LOD determines weight loss of the test sample due to sample drying that also includes water content, solvents and volatile impurities

Procedure for Loss on Drying:

Unless and until not described in monograph take 1 to 2 g of test sample.
Decrease the particle size to about 2 mm by use of motor pastel if required.
Set the drying oven temperature at a set specified temperature (Normally-105°C) (as per monograph) ± 2°C.
Take a glass stoppered LOD bottle with lid and keep in drying oven at specified temperature for 30 minutes.
After 30 minutes of drying remove the LOD bottle from the drying oven and cool it in at room temperature in a desiccator for 30 minutes.
Weigh an accurately empty bottle with a lid (W1). Add about 1.0 g sample into it and weigh (W2).
Place the LOD Bottle in a vacuum oven for prescribed times without a lid.
After drying is completed, open the vacuum oven, close the bottle carefully and allow it to cool at room temperature in a desiccator. Weigh the bottle along with the sample after drying (W3).

Note:

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 1 to 2 hours at a temperature 5° to 10° below the melting temperature, then dry at the specified temperature.
For Capsules are to be tested, use a portion of the mixed contents of not fewer than 4 capsules. In case of Tablets are to be tested, use powder from not fewer than 4 tablets

LOD Calculation:

(W2 – W3)

Loss on drying (% w/w) = —————– × 100

(W2 – W1)

Where,

W1 : Weight of empty LOD bottle in g

W2 : Weight of LOD bottle with Sample before drying in g

W3 : Weight of LOD bottle with sample after drying in g.

Measurement of LOD:

1. Thermogravimetric analysis (TGA), a sensitive electro balance or Moisture Analyzer

Moisture Balance for LOD — Moisture Balance

2. Vacuum Oven

What is the difference between water by KF and Loss on Drying (LOD)?

The significant difference between water by KF and LOD is, that Karl Fischer (KF) determines only moisture content in the test sample and LOD determines weight loss of the test sample due to sample drying that also includes water content, solvents and volatile impurities.

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