(i) Ascorbic acid (generally added to prevent oxidation of phenols) interferes in this assay and, therefore, should not be added to the solvent used for tannin extraction.
(ii) Rhodanine solution is stable for two weeks when stored in a refrigerator, stock solution of gallic acid diluted in H2SO4 can be kept in the refrigerator for one week and gallic acid dissolved in H2SO4 can be kept frozen for at least one month.
Experiment 5: Lignin Content (Refer Chapter 14, Experiment 6) 3.2 Terpenoids
Experiment 6: Total Azadirachtin-like Limonoids
Triterpenoids form conjugated diene groupings with H2SO4. Addition of vanillin transforms this complex to a blue chromophore that is detected at 577 nm (Dai etal., 1999).
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