2. Introduction
Alcohol is present as a major
component in most of gelanicals
There are 2 methods for its
determination
3. Distillation method.
4. Chromatographic method.
3. Things to consider- special treatments
Volatile acids & bases: render the
preparation containing volatile bases
slightly acidic with sulphuric acid and
acid with bases like NaOH
Glycerin: preparation should be diluted
in such a way that the residue after
distillation should not be less than 50%
water
Iodine: treat solutions with powdered
zinc or decolorize with sod. thiosulphate
and add few drops of NaOH.
4. Conti…
1. For liquids presumed to contain 50% v/v
alcohol or less.
Mix 25ml sample with equal volume of
water in a separator.
Saturate with NaCl & add 25ml hexane.
shake well to remove any interfering
volatile substance.
Draw lower layer and extract it again
with hexane.
Distil as usual and take volume having
simple ratio to original specimen.
5. Conti…
2. For liquids presumed to contain
more than 50% v/v alcohol.
Adjust the conc. of alcohol to
approximately 25% v/v by diluting
with water.
Perform the same procedure as
above.
6. Distillation method
Some precaution are taken
¡ Distillate should be clear, if cloudy, add
talc or CaCO3 and filter, adjust temp.
¡ Loss of alcohol should be minimized.
¡ Size of the flask should be 3-4 time
larger than volume of sample used.
¡ Frothing should be avoided by adding
H3PO4, H2SO4, tannic acid.
¡ Bumping can be avoided by adding
small pieces of broken glass, glass
beads or porous chips.
7. Method: For liquids presumed to contain
less than 30 % v/v alcohol
Take 25ml sample, add equal volume of
water and distil.
Collect distillate 2 ml less than the
original volume (23ml).
Add water to make it 25ml.
Adjust the temp and find specific gravity
or refractive index.
From Alcoholometric table find the %age
of alcohol.
8. For liquids presumed to contain more than 30 % v/v
alcohol
Take 25ml sample add 50ml water and
distil.
Collect distillate 2 ml less than 50ml
(48ml).
Add water to make it 50ml.
Adjust temp and find specific gravity or
refractive index.
From Alcoholometric table find the % age
of alcohol.
(the proportion of alcohol is ½ of liquid so multiply it
with 2 to get exact % age of alcohol in sample)
