Study Set Content:
- Sparingly soluble in water
- Soluble in most organic solvents
- Alkaloids (R3N) or free alkaloids:
- Soluble in water
- Sparingly soluble in immiscible solvents
Alkaloidal salts
- Reaction to acid Alkaloids combine directly with acids will form salts that are soluble in water but insoluble in certain organic solvents
- Reaction to acid Alkaloids combine directly with acids will form salts that are soluble in water but insoluble in certain organic solvents
water soluble salt formula
R3N + HCl= R3NH Cl
Reaction to base Alkaloids will be liberated from aqueous solutions when combine directly with
Alkalis
Alkaloids form highly insoluble precipitates with reagents that contain salts of
heavy metals
R3NH Cl + NaOH = R3N + NaCl + H2O
R3NH Cl + NaOH = R3N + NaCl + H2O
Sources of errors in Assaying Alkaloids
- Failure to secure complete extraction of the alkaloids from solution.
- Loss of volatile solvent during maceration of the drug before an aliquot portion is taken.
- Imperfect separation of immiscible liquids.
- Failure to wash properly the apparatus being used for the assay
- Decomposition of alkaloids
- Use of wrong indicators.
- Most alkaloids are precipitated from neutral or slightly acidic solution by:
Dragendorff’s reagent
Mayer’s reagent
Wagner’s reagent
Hager’s reagent
- (solution of potassium bismuth iodide) orange coloured precipitate.
Dragendorff’s reagent
- (potassium mercuric iodide solution) Cream coloured precipitate.
Mayer’s reagent
- (iodine in potassium iodide red-brown precipitate
Wagner’s reagent
(picric acid) yellow precipitate.
Hager’s reagent
Preparation of drugs for assay
- The drug should be pulverized to the required fineness
- Care should be taken to avoid the loss of water during the pulverization
Weighing for assay:
The accuracy should be within 10mg for quantities equal to 5g or over
The alkaloid-bearing drugs are extracted with one of the following methods:
- Maceration
- Percolation
- Continuous Extraction
- Accurately weighed powdered drug is dipped in a specified amount of solvent or mixture of solvents
Maceration
- Then made it alkaline with ammonia TS solution and mix well and allow to macerate for 12-14 hours with occasional shaking
Maceration
Afterwards allow the solvent to settle
Maceration
- Decant and aliquots of which are used for analysis
Maceration
