Vitamin A testing is the detection of vitamin A levels. Vitamin A, chemically known as retinol, was the first vitamin to be discovered. There are two types of vitamin A. One is vitamin A alcohol, which is the original form of vitamin A (found only in animal foods); the other is carotenoids, which are converted in the body into a preformed form of vitamin A (which can be ingested from plant and animal foods); and there are 3 units of measurement for vitamin A, including USP units, IU units, RE units, and so on.
Vitamin A measurement method:
1, principle: vitamin A in trichloromethane and antimony trichloride interaction, resulting in a blue substance, the depth of which is proportional to the amount of vitamin A contained in the solution. The blue substance is not stable, but its absorbance can be measured by spectrophotometer at 620nm within a certain period of time.
2, instrumentation laboratory equipment commonly used spectrophotometer reflux condensing device.
3, the reagents used in this experiment are analytically pure, the water used is distilled water.
(1) anhydrous sodium sulfate Na2SO4;
(2) acetic anhydride;
(3) ether does not contain peroxide;
(4) anhydrous ethanol does not contain aldehydes;
(5) trichloromethane should be free of decomposition, or it will destroy the vitamin A. Checking method: trichloromethane is unstable, and it is susceptible to the action of oxygen in the air. The checking method: trichloromethane is not stable, and it is easy to generate hydrogen chloride and phosgene by the action of oxygen in the air. When checking, take a small amount of trichloromethane and put it in a test tube with water and shake it, so that hydrogen chloride dissolves into the water layer. Add a few drops of silver nitrate solution, if the white precipitate that is, trichloromethane decomposition products;
(6) 25% antimony trichloride - trichloromethane solution Prepare 25% antimony trichloride solution with trichloromethane, stored in a brown bottle (pay attention to avoid absorbing water);?
(7) 50% potassium hydroxide solution (KOH) W/V;
(8) Vitamin A standard solution Retinol (purity 85% Sigma) Dissolve the vitamin A standard with de-formalized ethanol to a concentration of approximately 1 ml equivalent to 1 mg of retinol. Calibrate the exact concentration by UV spectrophotometry before use;
(9) Phenolphthalein indicator Prepare a 1% solution with 95% ethanol.