Introduction Alcohol is present as a major component in most of gelanicals There are 2 methods for its determination3. Distillation method.4. Chromatographic method.
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.
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.
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.
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.
Method: For liquids presumed to containless 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.
For liquids presumed to contain more than 30 % v/valcohol 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)