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Extraction of Alkaloids: Pharmacognosy Lab

The document describes the extraction of alkaloids from coffee seeds and the chemical tests used to identify alkaloids. Key steps include: 1) Powdering coffee seeds and extracting with water then filtering the aqueous extract. 2) Adding sulfuric acid and charcoal to unmask alkaloids then separating the filtrate into chloroform and aqueous layers. 3) Testing the layers using Dragendorff's reagent and picric acid, which can identify alkaloids through the formation of precipitates.

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nicee willaine
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563 views1 page

Extraction of Alkaloids: Pharmacognosy Lab

The document describes the extraction of alkaloids from coffee seeds and the chemical tests used to identify alkaloids. Key steps include: 1) Powdering coffee seeds and extracting with water then filtering the aqueous extract. 2) Adding sulfuric acid and charcoal to unmask alkaloids then separating the filtrate into chloroform and aqueous layers. 3) Testing the layers using Dragendorff's reagent and picric acid, which can identify alkaloids through the formation of precipitates.

Uploaded by

nicee willaine
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We take content rights seriously. If you suspect this is your content, claim it here.
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PHARMACOGNOSY LAB TESTS/REAGENTS.

EXTRACTION OF ALKALOIDS  Wagner’s test


- Common test
- Contains Iodine in Potassium iodide (KI)
ALKALOIDS.
- (+): red-brown precipitate
- One of the significant groups of plant compounds
 Mayer’s test
- One of the very physiologically active plant compounds
- Common test
- Nitrogen-containing
- Highly-reactive - Contains Mercuric Potassium iodide (KI)
- Synthesized from amino acids - (+): cream/white precipitate
 Valser’s test
EXTRACTION OF ALKALOIDS FROM COFFEA - Contains Mercuric iodide
ARABICA SEEDS.  Dragendorff’s test
- 25 grams powdered coffee seeds + 130 mL distilled - Most common test
water - Contains Potassium bismuth iodide
 Triturate coffee seeds with mortar and pestle - (+): red-brown/orange precipitate
 Coffea arabica: contains caffeine  Marmes test
 Caffeine [1,3,7-trimethylxanthine]: CNS - Contains Cadmium in Potassium iodide (KI)
stimulant; used to treat migraine; purine  Sonnencheins test
alkaloid - Contains phosphomolybdic acid
- Heat for 15 minutes with constant stirring  Schcibler’s test
- Expression using a muslin cloth - Contains phosphototungstic acid
 filter aqueous extract with muslin cloth  Picric acid test [Hagers test]
- Filtrate + 5 mL Magnesium acetate - (+): yellow precipitate
 Precipitating agent: magnesium or lead  Tannic acid
acetate  Gold salts
- Heat the mixture until boiling
- Add 1 mL sulfuric acid + 0.5 g charcoal
 add acidifying agent [can also be HCl]
 Acidifying agent: Unmasks the presence of
alkaloids in the extract solution
 Charcoal: decolorizing agent; purifies the
solution
- Filter to separate charcoal
- Filtrate + 100 mL Chloroform [or ethanol]
 Chloroform: halogenated and semi-polar
solvent
 Most alkaloids are soluble in chloroform
- After adding chloroform, a 2 phase mixture forms
- Collect the chloroform [lower layer]
 Decantation or using a Separatory funnel
 Layer with more density settles at the bottom
of the separatory funnel [denser than water]
- Collect the aqueous layer [upper layer]
 Subject to rotary evaporation to obtain
caffeine-containing solution
 Can also be crystallized

CHEMICAL TESTS.
- Samples:
 Chloroform [lower layer]
 Aqueous layer [upper layer]
- Test Tube 1
 Chloroform layer sample 3 mL + 3 gtts of
Dragendorff’s reagent
- Test Tube 2
 Chloroform layer sample 3 mL + 3 gtts of
picric acid solution
- Test Tube 3
 Aqueous layer sample 3 mL + 3 gtts of
Dragendorff’s reagent
- Test Tube 4
 Aqueous layer sample 3 mL + 3 gtts of picric
acid solution

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