Study Set Content:
Calculation of the weight of a substance in a sample from the weight of a chemically equivalent amount of some other substances
Gravimetric analysis
The substance to be measured is separated from the sample by physical or chemical methods that convert the substance to a chemically equivalent amount of some other substance which can be separated, purified, and weighed.
Gravimetric analysis
Official USP Gravimetric Methods:
• Assay involving Direct Ignition
• Assay involving extraction
• Assay involving Precipitation followed by ignition.
GRAVIMETRIC FACTOR( E )
Formula
E = Analyte
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Residue
The residue remaining after incineration is the ash content of the drug.
Ash Value
Inorganic salts of
carbonates, phosphates, silicates of sodium, potassium, calcium and magnesium.
is a criterion to judge the identity or the purity of the crude drug.
Ash Value
is indicative of contamination, substitution, adulteration or carelessness in preparing the crude drug for marketing.
High ash value
is used as a basis for the identity and cleanliness of a drug.
Ash content
This also gives information about adulteration with inorganic matter.
Ash content
- is a measure of the amount of inorganic matter present as impurity.
The ash or residue yielded by organic matter
Ash value can be determined by three different methods:
Total Ash
Acid Insoluble Ash
Water soluble Ash
method is used to measure the total amount of material remaining after incineration.
Total Ash
is the residue obtained after boiling the total ash with dil. HCl and igniting the remaining insoluble matter.
Acid Insoluble Ash
is the difference in weight between total ash residue after treatment of total ash with water.
Water Soluble Ash
Total Ash procedure
Weight accurately about 3 gms of the powdered drug in tared silica crucible
Heat at 450 C until free from carbon
Cool and weigh
Acid Insoluble Ash methods
Total Ash
Add 10 mL 3N HCl and boil for 5 mins.
Filter through ashless filter paper
Ignite at 450 C
Cool and weigh
Water Soluble Ash methods
Total Ash
Add 10 mL and boil for 5 mins.
Filter through ashless filter paper
Ignite at 450 C
Cool and weigh
Very dull red heat
500-550 C
Dull red heat
550-700 C
