[24] Colorimetric estimation of vitamin A with trichloroacetic acid

Add time:07/16/2019    Source:sciencedirect.com

Publisher SummaryThis chapter discusses the use of trichloroacetic acid method for colorific estimation of vitamin A in serum and liver tissue. In this method, trichloroacetic acid crystals (50 g), freshly washed with solvent, are dissolved in alcohol-free distilled chloroform (25 ml). This gives about 50 ml of reagent that is stable for 5 h with daylight excluded. Optical density readings tend to decrease with storage for longer periods, up to 24 h. No color is given by vitamin A with reagent exposed to bright diffuse sunlight for several hours. It is observed with this method that the colors produced from vitamin A, its acetate, and palmitate with the Carr-Price antimony trichloride reagent and trichloroacetic acid reach the same intensity for any given amount of vitamin. The concentration of trichloroacetic acid controls the rate of formation and stability of anhydrovitamin, which may be correlated with loss of vitamin A or its acetate. It is important to observe that change occurs without appearance of blue color in the weaker acid medium. Formation of anhydrovitamin with fine-structure absorption follows protonation of vitamin A, and the slower formation from vitamin A acetate reflects differences in the rates of dehydration and deacetoxylation.

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