Iodine Test-Definition, Principle, Procedure, Result, Uses

Iodine Test Definition

The Iodine test is a chemical process which distinguishes particular polysaccharides, including amylase, dextrin, as well as glycogen, from mono-or disaccharides. The starch-iodine test, a variation of this method, is utilized to identify the existence of glucose generated by plants in leaf tissue.

Objectives of the Iodine Test

  • determining the availability of starch and other polysaccharides.

Principle of Iodine Test

  • The iodine test is based on the polyiodide ions that generate colourful adsorption compounds with the helical chains of glucose leftover from amylase (blue-black), dextrin (black), or glycogen (reddish-brown).
  • Branched polysaccharides like cellulose, monosaccharides, and disaccharides all maintain their colorlessness. An orange-yellow colour is produced by amylopectin.
  • The iodine test utilises Lugol’s iodine, an aqueous solution comprising elemental iodine as well as potassium iodide.
  • Iodine cannot dissolve in water on its own. A reversible interaction between potassium iodine and iodine produces a triiodide ion, which subsequently combines with an iodine molecule to form a pentaiodide ion.
  • The iodide, triiodide, as well as pentaiodide ions are generally colourless, whereas bench iodine solution appears brown.
  • It has been noticed that the helix (or coil or spring) shape of the glucose chain is crucial to this assay.
  • The distance between the glucose chains also impacts the final colour.
  • The resulting linear triiodide and pentaiodide ions slide into the helix framework.
  • The complex’s colour is believed to result from variances in the spacing of the energy levels, which may absorb visible light as a consequence of the charge transfer between the helix and the polyiodide ions.
  • When the temperature rises and there are organic molecules like ethanol present that are water soluble, the colour intensity drops.
  • Because of the disruption of the helical structure during heating, the blue colour and iodine binding ability of the amylase-iodine complex dissociate and then reassemble upon cooling.
  • After cooling, the blue hue returns as a result of the helical structure recovering its ability to bind iodine.


      1. Reagent

  • To create Lugol’s iodine, 5 percent elemental iodine is combined with 10 percent potassium iodide.
  • Test sample
  1. Materials Required
  • Test tubes
  • Test tube stand
  1. Equipment
  • Water bath

Procedure of Iodine Test

  1. Put 1 ml of the sample that is provided in a dry, clean test tube.
  2. In another tube, take control of 1 cc of distilled water.
  3. To each tube, add a few drops of Lugol’s solution, then swirl them together.
  4. Watch how the test tubes’ appearance changes colour.
  5. The test tubes should be heated in the water bath until the colour is gone.
  6. Remove the test tubes so they can cool down.
  7. Keep a record of the coloration in the test tubes.

Results and Interpretation of the Iodine Test

  • A positive test result is when a blue-black or purple hue appears; this shows that starch is present.
  • When the colour doesn’t really alter, the result is unfavourable and indicates the absence of starch.

Uses of Iodine Test

  • This test is employed to find starch in a variety of materials.
  • Similar to that, this test is run to evaluate how well plants’ photosynthesis works.

Limitations of the Iodine Test

  • Since starch hydrolyzes in acidic environments, this test cannot be carried out there.
  • This test is qualitative in nature and does not reflect starch content.

References and Sources

  • Tiwari A. (2015). Practical Biochemistry. LAP Lambert Academic Publishing.
  • 2% – https://allmedicalstuff.com/barfoeds-test/
  • 1% – https://www.scribd.com/document/429888468/Advances-in-Carbohydrate-pdf
  • 1% – https://www.coursehero.com/file/p39m2q7c/IKI-Test-experiments-the-presence-of-starch-in-a-solution-if-positive-color/
  • 1% – https://libraryofessays.com/lab-report/lap-report-1895512
  • <1% – https://allmedtests.com/iodine-test-starch/
Spread the love

Leave a Comment

Your email address will not be published. Required fields are marked *