This document describes methods for determining the moisture content of crude drugs, including loss on drying and azeotropic distillation. Loss on drying is the common gravimetric method, which involves weighing a sample before and after drying in an oven at 100°C until the weight is constant. Azeotropic distillation is a volumetric method that uses toluene to distill any water in a sample into a graduated tube, allowing the volume of water to be measured and moisture content calculated based on the sample weight. Other instrumental methods like gas chromatography and NMR are also mentioned. The key steps of each technique are outlined.

1. Determination of moisture
content of crude drugs
Prepared by : Masarrat M. Khan.
Designation: Assistant Professor
College: YB. Chavan College of Pharmacy,
Aurangabad.

2.  Reference:
1. “Practical Pharmacognosy Techniques and
Experiments” by Dr.K.R. Khandelwal, Dr.
Vruna Sethi, Nirali Prakashan, Page no:
23.6-23.7
2. Quality control methods for medicinal plant
materials, WHO, Geneva.

3. Method for Determination of
Moisture Content
• loss on drying
Gravimetric
• Azeotropic distillation
Volumetric
• Gas Chromatography
• NMR
Instrumental

4. DETERMINATION OF LOSS ON
DRYING (LOD)

5. Preparation of material
 Prepare a suitable quantity of the sample by
cutting, granulating or shredding the unground
or unpowdered material, so that the thickness of
the parts does not exceed 3 mm.
 Seeds or fruits smaller than 3 mm should be
cracked.
 Avoid the use of high-speed mills in preparing
the sample, and take care that no appreciable
amount of moisture is lost during preparation.
 It is important that the portion is large enough to
be a representative sample.

6. Gravimetric Method
 Procedure:
 Weigh about 1.5 g of the powdered drug into
a weighed flat and thin porcelain dish.
 Dry in the oven at 100oC or 105oC, until two
consecutive weighing do not differ by more
than 0.5 mg.
 Cool in desiccators and weigh. The loss in
weigh in usually recorded as moisture.

7.  Note:
 A very useful from dish for the determination of moisture is a
thin flat porcelain dish. If a platinum dish is available it may be
used.
 The burning of the powder should proceed slowly and the
material must not be allowed to catch fire or to give off smoke
as dense fumes.
 The desiccation method is useful for materials that melt to a
sticky mass at elevated temperatures.
 The most common method for the determination of moisture
is heat the drug till one gets constant weight at 100o, as is
done for digitalis.
 However, many substances loose other volatile constituents,
or some of their constituents undergo change with
consequent loss of weight at a temperature of 100o, other
methods are used for materials of these types.
 If the solvent is anhydrous, water may remain absorbed in it
leading to false results. Hence, it is advisable to saturate the
solvent with water before use.

8. Azeotropic method (toluene
distillation)
 The apparatus consists of a
 Glass Flask (A)
 Connected by a tube (D)
 D is connected to a Cylindrical Tube (B)
 B is fitted with a graduated receiving tube (E) and
 A Reflux Condenser (C).
 The receiving tube (E) is graduated in 0.1-ml
divisions so that the error of readings does not
exceed 0.05 ml. The preferred source of heat is
an electric heater with a rheostat control, or an
oil-bath.
 The upper portion of the flask and the connecting
tube may be insulated.

10. Procedure
 Thoroughly clean the receiving tube and
the condenser of the apparatus, rinse with
water and dry.
 Introduce 200 ml of toluene R and about 2
ml of water into a dry flask.
 Heat the flask to distil the liquid over a
period of 2 hours, allow to cool for about
30 minutes and read off the volume of
water to an accuracy of 0.05 ml (first
distillation).

11.  Weigh accurately a quantity of the material
expected to give about 2-3 ml of water and
transfer to the flask. (For weighing material with a
paste-like character, use a boat of metal foil.) Add
a few pieces of porous porcelain and Quality
control methods for medicinal plant materials
 heat the flask gently for 15 minutes. When boiling
begins, distil at a rate of 2 drops per second until
most of the water has distilled over, then increase
the rate of distillation to about 4 drops per second.
As soon as the water has been completely
distilled, rinse the inside of the condenser tube
with toluene R. Continue the distillation for 5 more
minutes, remove the heat, allow the receiving tube
to cool to room temperature and dislodge any
droplets of water adhering to the walls of the
receiving tube by tapping the tube.
 Allow the water and toluene layers to separate
and read off the volume of water (second

12.  Calculate the content of water as a
percentage using the formula:
 where w = the weight in g of the material
being examined
 n = the number of ml of water obtained in
the first distillation
 n1 = the total number of ml of water
obtained in both distillations