Purpose: Colorimetric spot test for alkaloids, especially morphine and codeine.
Procedure:
Slowly add 1 ml concentrated sulfuric acid to 1 ml of cold fuming nitric acid in a chilled container.
Mix well and use immediately.
⚠️ Use extreme caution due to strong acids and fumes.
Dragendorff’s Reagent
Purpose: Detection of alkaloids in plant extracts or formulations.
Procedure (stock solution method):
Stock A: Dissolve 1.7 g bismuth subnitrate in 20 ml glacial acetic acid.
Stock B: Dissolve 40 g potassium iodide in 100 ml distilled water.
Mix 10 ml of A and 20 ml of B.
Dilute with distilled water to make 100 ml.
Store in a dark bottle; stable for weeks.
Tollen’s Reagent
Purpose: Detects aldehydes (reducing agents).
Procedure:
Prepare fresh before use:
Mix 2 ml of 0.1 M silver nitrate solution.
Add a few drops of dilute NaOH to form Ag₂O precipitate.
Add dilute ammonia dropwise until the precipitate just dissolves.
Seliwanoff’s Reagent
Purpose: Differentiates between aldose and ketose sugars.
Procedure:
Dissolve 0.05 g resorcinol in 100 ml of 3M HCl.
Store in an amber bottle.
Biuret Reagent
Purpose: Detects proteins (peptide bonds).
Procedure:
Dissolve 1.5 g CuSO₄·5H₂O in 500 ml distilled water.
Add 6 g sodium potassium tartrate and 375 ml of 10% NaOH.
Make up to 1000 ml with distilled water.
Barfoed’s Reagent
Purpose: Differentiates between monosaccharides and disaccharides.
Procedure:
Dissolve 66.5 g copper(II) acetate in 1000 ml distilled water.
Add 9 ml glacial acetic acid.
Mix thoroughly and store in a dark bottle.
Molisch’s Reagent
Purpose: A general test for carbohydrates.
Procedure:
Dissolve 5 g of α-naphthol in 100 ml of ethanol (95%).
Store in a dark bottle.
