hydroiohc acid alone, hydroiodic acid and hydrochloric acid or acetic acid and starch and hydroiodic acid and starch were found reacting well with the rancid groundnut oil, as they developed colour when sprayed on tlc plates. They were found silent for castor and fresh groundnut oils.
Ferrous thiocyanate gave brown spot for rancid groundnut oil due to oxidation of ferrous ions into femc ions, by peroxides, and subsequent complex formation with thiocyanate portionofthereagent.Theintensity ofspot faded away with time while keeping the plate at room temperature. Permanent blue spot for rancid groundnut oil was developed by spraying the tlc plate with potassium io&de and starch solutions. Even trace quantities of peroxides can be detected by the oxidation of iodide to iodine'>, which complexes with starch and gives blue or brown colour. This is again true whenever hydroiodic acid is used in place of potassium iodide. Certain combinations of hydrochloric and acetic acids were also successfully tried to boost the process of oxidation reduction reaction during the investigation. In absence of starch liberated iodine from hydroiodic acid gave only yellow coloured spot which turned blue on spray of starch solution. Alkaline potassium permanganate solution developed a yellow spot, when sprayed for rancid groundnut oil. In all these estimations castor and fresh groundnut oils were found silent, as no spot could be seen by the above spray reagents as expected.
Few reagents, namely, 2,4-DNP and ethanolamine, phenolphthalein, chromic acid and ammonical silver nitrate &d not work at all, may be due to their specific chemical nature.