ALCOHOL DETERMINTION
Distillation:
The process of purifying a liquid by a process of heating followed by cooling is called
distillation.
General Method/Description:
This is a general method for determination of alcohol, unless otherwise specified in the
monograph. It is suitable for examination of most of fluid extracts and tinctures. The rate
of distillation should be such, that produces clear distillates are produced. If distillates are
cloudy, they may be clarified by agitating with talc or precipitated calcium carbonate.
Then the distillate is filtered and temperature of distillate is adjusted. Finally the alcohol
content are determined by measuring specific gravity.
Standard alcoholometric table, which relates specific gravity with percentage of alcohol
by volume or by weight at different temperature, is used to ensure the contents of alcohol.
During all manipulations, take precautions to minimize the loss of alcohol by
evaporation.
Problems during distillation of alcohol:
Following are the problems which are encountered during process of distillation.
i. Frothing:
Froth: It is a mass of small bubbles produced in a liquid after agitation of a liquid is
called froth.
Treat the liquid that froth to a troublesome extent during distillation by rendering
(providing) them either
Strongly acid which may be phosphoric Acid, sulfuric acid or tannic acid as
described in official monograph.
(OR)
Treat with slight access of calcium chloride solution
(OR)
Treat with small amount of paraffin or silicone oil before starting the distillation.
ii. Bumping:
It is defined as knocking out or run out of a material from another with a jolt is
called bumping.
Prevent bumping during distillation by adding porous chips of insoluble material
such as silicon carbide or beads.
Method for liquids presumed to contain less than 30% alcohol:
Take a suitable distillation apparatus and wash it properly with water.
Transfer the sample, from which alcohol is to be determined, to distillation flask
with the help of pipette.
The sample should not be less than 25ml.
Adjust the temperature as specified in the monograph.
Add equal volume of water and start the process of distillation.
Collect a volume of distillate about two ml less than the volume taken for original
test liquid .i.e. 23 ml.
Adjust the temperature of distillate at which original test liquid was measured.
Add sufficient amount of water to distillate (upto 25ml i.e. 2ml) and mix
thoroughly.
Distillate should be clear or not more than slightly cloudy.
It should not contain more than traces of volatile substances other than alcohol and
water.
Add this distillate to pycnometer, adjust the temperature at 25o C unless otherwise
specified in the monograph and find the specific gravity of distillate.
Determine the percentage of alcohol in distillate by comparing the specific gravity
of distillate with alcoholometric table.
Method for liquids presumed to contain more than 30% alcohol:
Take a suitable distillation apparatus and wash it properly with water.
Transfer the sample, from which alcohol is to be determined, to distillation flask
with the help of pipette.
The sample should not be less than 25ml.
Dilute the test sample with water at about twice its volume i.e. 50 ml of water
Adjust the temperature as specified in the monograph and start the process of
distillation.
Collect a volume of distillate about two ml less than twice the volume taken for
original test liquid .i.e. 48 ml.
Adjust the temperature of distillate at which original test liquid was measured.
Add sufficient amount of water to distillate (50ml) and mix thoroughly.
Distillate should be clear or not more than slightly cloudy.
It should not contain more than traces of volatile substances other than alcohol and
water.
Add this distillate to pycnometer, adjust the temperature at 25o C unless otherwise
specified in the monograph and find the specific gravity of distillate.
The portion of alcohol by volume, in the distillate, as assured from its specific
gravity, equals one half that in liquid examined. It is then multiplied by 2 to get the
percentage of alcohol in liquid examination.
Special treatments:
Volatile acids and bases:
render preparation containing volatile bases slightly acidic with diluted sulfuric
acid before distilling. If volatile acids are present, render the preparation slightly
alkaline with sodium hydroxide test solution.
Glycerin:
To liquid that contain glycerin, add sufficient water so that the residue, after
distillation contains at least 50% of water.
Iodine:
Treat all solutions containing free iodine with powdered zinc before the distillation
or decolorize with just sufficient sodium thiosulfate solution followed by few
drops of sodium hydroxide test solution.
