In most of the galenical preparations, alcohol is used. There are two methods for the determination of alcoholic contents.
DISTILLATION METHOD.
GAS LIQUID CHROMATOGRAPHY.
DISTILLATION METHOD
This is the general method used for the determination of alcohol, unless specified in the individual monograph.
This method is suitable for examining most fluid extracts and tinctures, provided the capacity of distillation flask is sufficient (commonly 2-4 times the volume of the liquid to be distilled) and the rate of distillation is such that clear distillates are produced. Cloudy distillates may be clarified by agitation with TALC or with white ppt of CaCO3 and filtered after which the temperature of the filtrate is adjusted and the alcohol contents are determined from the specific gravity given is B.P.
PRECAUTIONS:
During all procedure minimize the loss of alcohol by evaporation.
Bumping may be prevented during distillation by making the solution alkaline with milk of magnesia or by adding porous chips of insoluble material glass or capillary tubes each sealed off at one end.
Frothing: treat the liquids that froth to a troublesome extent during distillation by rendering them strongly acidic with phosphoric sulfuric or tannic acid or treat them with a slightly excess of CaCl2 solution or with a small amount of paraffin or silicone oil before starting the distillation.
(A). FOR LIQUIDS PERSUMED TO CONTAIN LESS THAN 30% OF ALCOHOL:
Take 25ml of the sample in the distillation flask.
Add some amount of distilled water mixed and distilled it.
Take the distillate 2ml less than the original sample.
Bring the temperature at which the procedure was started.
Add sufficient amount of distilled water to the distillate to make volume 25ml.
Calculate the specific gravity and note the percentage of alcohol from the table given in B.P.
(B). FOR LIQUIDS PERSUMED TO CONTAIN MORE THAN 30% OF ALCOHOL:
Take 25ml of the sample in the distillation flask.
Add twice the volume of distilled water.
Mix and distill it.
Take the distillate 2ml less than the double amount of sample.
Bring the temperature at which the procedure was started
Add sufficient amount of distilled water to make the volume 50ml.
Calculate the specific gravity and note the percentage of alcohol from the table given in B.P.
SPECIAL TREATMENT:
VOLATILE ACIDS AND BASES: The preparations that are basic in nature are treated with dilute H2SO4 before distillation and the preparations that are acidic in nature are treated with NaOH solution before distillation.
GLYCERIN: To the liquids containing glycerin, add sufficient amount of water so that residue after distillation contain 50% of water.
IODINE: All the solutions containing free Iodine should be treated with Zinc before the distillation or decolorize with Nathiosulphate followed by a few drops of NaOH.
OTHER VOLATILE SUBSTANCES: When spirits elixirs, tinctures and similar preparations contain volatile materials other than alcohol such as volatile oils, chloroform, ether, camphor, they require special treatment as follows:
(A). FOR LIQUIDS PRESUMED TO CONTAIN LESS THAN 50% OF ALCOHOL:
For example: SPIRIT CHLOROFORM
Take 25ml in a separating flask.
Add to it 50ml of brine solution, i.e. saturated solution of NaCl.
Add 40ml of petroleum ether or petrol and shake for 2 minutes then take the lower layer.
Add again 50ml of brine solution to the separating flask and take the lower layer i.e. aqueous layer.
Distill whole of the aqueous solution containing brine solution. The distillate equal to the volume of original sample is collected.
Calculated the specific gravity and noted its percentage from the table given in B.P.
(B). FOR LIQUIDS PRESUMED TO CONTAIN MORE THAN 50% OF ALCOHOL:
Adjust the sample up to 25% alcohol by diluting it with water then proceed as given in the procedure above.
EXAMPLE:
ALCOHOLIC CONTENTS IN EXTRACT GLYCYRRHIZA:
To 25ml sample add 40ml of N/10 H2SO4 into distillation flask.
Add 70ml of water.
Collect the distillate about 70ml.
Add water to it and make the volume to 100ml.
Calculate the specific gravity and note its percentage from the table given in B.P.
GAS LIQUID CHROMATOGRAPHY (GLC):
APPARATUS: The instrument contains a column of 2mm by 4mm packed with polyethylene glycol.
The column is maintained at 100C.
The injection part is equipped with a solid filter and is maintained at 160C.
An inert gas such as gallium is used as carrier at a flow rate of about 60ml per minute.
STANDARD SOLUTIONS:
For liquids containing more than 10% alcohol, prepare two standard solutions, one with 5% less and one with 5% greater concentration than the expected concentration of the sample.
Standardize them by calculating its specific gravity and noting the percentage from the table given in B.P.
For liquids containing less than 10% alcohol, prepare two standard solutions one with 1% less and one with 1% greater concentration than the expected concentration of the sample. Standardize them by calculating specific gravity and noting the percentage from the table given in B.P.
PROCEDURE:
Treat the sample and each of the standard solution as followed:
Take 25ml in a container with stopper.
Add 10ml of internal standard (Acetone) for each 6ml of alcohol.
Mix and add water if necessary.
Inject appropriate quantity into the apparatus.
From the chromatogram obtained, we can calculate the percentage of alcohol as by using the following formula:
[S1 (Y-Z)+S2 (Z-X)]
(Y-X)
Where:
S1: %age of alcohol in standard solution 1.
S2: %age of alcohol in standard solution 2.
X, Y and Z are the ratio of alcohol peak area to the internal standard peak areas for the standard solution 1, standard solution 2 and the sample respectively.
No comments:
Post a Comment