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Phytochemical Screening Techniques

  • Botany
  • In this phytochemical screening techniques post we have briefly explained about Alkaloids, flavonoids, tannins, saponins, flavones, sterols, terpenes, cardiac glycosides, protein, carbohydrates, and lipids.

Phytochemical Screening Techniques

  • Preliminary procedures to detect the presence of both primary and secondary metabolites in an extract are known as Phytochemical Screening. Alkaloids, flavonoids, tannins, saponins, flavones, sterols, terpenes, cardiac glycosides, protein, carbohydrates, and lipids were detected using the qualitative analyses outlined below.

Alkaloids

Dragendorff’s test

  • 1mL of extract was taken and placed into a test tube. Then 1mL of potassium bismuth iodide solution (Dragendorff’s reagent) was added and shaken. An orange red precipitate formed indicates the presence of alkaloids.

Wagner’s test

  • 1mL of extract was taken and placed into a test tube. Then 1mL of potassium iodide (Wagner’s reagent) was added and shaken. Appearance of reddish brown precipitate signifies the existence of alkaloids.

Mayer’s test

  • 1mL of extract was taken and placed into a test tube. Then 1mL of potassium mercuric iodide solution (Mayer’s reagent) was added and shaken. Emergence of whitish or cream precipitate implies the presence of alkaloids.

Hager’s test

  • 1mL of solution of an extract was taken and placed into a test tube. Then 1mL of saturated ferric solution (Hager’s reagent) was added and shaken. Formation of yellow-colored precipitate indicates the existence of alkaloids.

Glycosides

Bontrager’s test

  • One gram of the crude extract was first weighed, placed into a test tube, and dissolved in 5mL of dilute hydrochloric acid. Then 5mL of ferric chloride (5%) solution was added. The mixture was shaken and placed over water bath. Then the mixture was allowed to boil for 10min, cooled, and filtered. Afterward, the mixture was then extracted again with benzene. Finally, equal volume of ammonia solution was added to benzene layer. Appearance of pink color indicates the presence of anthraquinone glycosides.

Legals test

  • 1mL of an extract was taken, and then an equal volume of sodium nitroprusside was added followed by few quantity of sodium hydroxide solution and shaken. Formation of pink-to-blood-red precipitate signifies the existence of cardiac glycoside.

Keller-Killiani test

  • 2mL of the extract was taken and diluted with equal volume of water. Then 0.5mL of lead acetate was added, shaken, and filtered. Again, the mixture was extracted with equal volume of chloroform, evaporated, and dissolved the residue in glacial acetic acid. Then few drops of ferric chloride were added. Again, the whole mixture was placed into a test tube containing 2mL of sulfuric acid. Emergence of reddish brown layer that turns bluish green implies the presence of digitoxose.

Steroids and triterpenoids

Burchard’s test

  • This method is utilized for an alcoholic extract. Extract need to dry out first through evaporation, then extracted again with chloroform.Add few drops of acetic anhydrites followed by sulfuric acid from the side of the test tube. Formation of violet to blue-colored ring at the junction of the two liquids indicated the presence of steroids.

Salkowski’s test

  • 1mL solution of the extract was taken and 2mL of chloroform was added, shaken, and filtered. Few drops of concentrated sulfuric acid were added to filtrate, shaken, and allowed to stand. Development of golden-yellow precipitate indicates the presence of triterpenes.

Tannins

Beater’s skin test

  • A Gold Beater’s Skin was obtained from Ox skin. The Gold Beater’s Skin was soaked in 2% hydrochloric acid and washed with distilled water. Then it was placed in a solution of an extract for 5min and washed with distilled water. Finally, it was placed in 1% ferrous sulfate solution. If the Gold Beater’s Skin changed to brown or black tannins is present.

Gelatin’s test

  • 1mL of extract was taken and placed in a test tube. Then 1% gelatin solution contains sodium chloride added and shaken. Appearance of white precipitate indicates the presence of tannins.

Flavonoids

Shinoda’s test

  • 1mL of extract was taken and placed into a test tube. Then, few drops of concentrated hydrochloric acid was added followed by 0.5mg of Rimandoium turnings and shaken. Emergence of pink coloration indicates the presence of flavonoids.

Lead acetate test

  • To detect the presence of flavonoids, 1mL of extract was taken and placed into a test tube. Then few drops of lead acetate added and shaken. Formation of yellow precipitate signifies the presence of flavonoids.

Alkaline test

  • 1mL of extract was taken and placed into a test tube. Then few drops of sodium hydroxide solution were added and shaken. Emergence of intense yellow color that turns to colorless after adding dilute acid implies the existence of flavonoids.

Phenols

Ferric chloride test

  • 1mL solution of an extract was taken and placed into a test tube. Then 1% gelatin solution containing sodium chloride was added and shaken. Formation of bluish-black color indicates the presence of phenols.

Lead acetate test

  • 1mL solution of an extract was taken and placed into a test tube. Then 1mL of alcoholic solution was added, followed by dilution with 20% sulfuric acid. Finally, solution of sodium hydroxide was added. Formation of red-to-blue color signifies the occurrence of phenols.

Gelatin test

  • A solution of plant extract was placed into test tube followed by 2mL of 1% gelatin solution and shaken. Appearance of white precipitate indicates the presence of phenols.

Mayer’s test

  • To a solution of plant extract, 1mL of Mayer’s reagent was added in an acidic solution. Manifestation of white precipitate shows the existence of phenolic compounds.

Protein

Biuret test

  • Some quantity of an extract was taken and 4% sodium hydroxide solution of the drug was produced. This is followed by the addition of 1 % copper sulfite. Appearance of violet color implies the existence of peptide linkage.

Ninhydrin test

  • 1mL of an extract was taken and placed into a test tube. Then 0.25% of ninhydrin reagent was added and shaken. The mixture was then boiled for few minutes. Formation of blue color signifies the presence of protein.

Xanthoproteic test

  • 1mL of the extract was taken and placed it into a test tube. Then few drops of nitric acid were added and shaken. Emergence of yellow-color indicates presence of protein.

Further Readings

Reference