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, Purpose:
1. Learn
general principles of quantitative determination of vitamin
C, and master the basic operating techniques for measuring vitamin C in food and biological fluids with a statutory amount of 2,6-dechlorophenol titration.
2. Get an overview of the physiological significance of vitamin C and its content in fresh fruits and vegetables.
, principle:
vitamin C is one of the essential vitamins in the human diet, if the lack of vitamin C, will lead to scum disease. Therefore, vitamin C, also known as astrain acid, has the effect of preventing and treating ascertic disease. Aspirin is widely distributed in nature and is found in fresh fruits and vegetables, especially lemon fruits and some green plants (e.g. green peppers, spinach, etc.).
assachic acid has a wide range of physiological functions in the body, it is known that the metabolic reaction of many important substances in the body needs astrochic acid participation. It is a coenzyme of proline hydroxylase, so it has the effect of improving collagen synthesis. Many enzymes containing sparse foundation in the body need to rely on the protection of assachtic acid as a reducing agent, so that the dredging of enzyme molecules is reduced, thus maintaining its catalytic activity. Due to the redox effect of astrohemic acid, it can promote the synthesis of
immunoglobulin
and enhance the body's resistance. It also converts oxidized glutathione
into
as a prototype glutathione (GSH), which can be released from the body in combination with heavy metals, so vitamin C is often used for detoxification of heavy metals. In addition, asyrotic acid still has many other physiological functions, but its action is not very clear.
assahitic acid is an unsaturated polyhydroxynester
compound
, slightly acidic sugar white crystals, soluble in water, so belongs to the water-soluble vitamin. In the solution of the molecule C2 and C3 between the oleol hydroxyl hydrogen is very easy to dissocilate and release H-plus, and oxidized into dehydrogenated assofhitic acid, oxidation still has the physiological activity of vitamin C, but it is easy to break down into di ketone glucosic acid, this compound no longer has the physiological activity of vitamin C. Vitamin C is highly reductive and is easily destroyed by oxidation when
is
in alkaline solutions and oxidants are present. Prototypes and oxidized assailtic acids can be transformed into
-
systems in biological tissues.
Because of the nutritional and clinical importance of vitamins, the determination of vitamin content in food and biological materials is very necessary. There are many quantitative measurement methods of asbic acid, such as 2,6-dichlorophenol (DCIP) titration, iodine titration, 2,4-dinitrobenzene method, Folin
reagement
color ratio, ultraviolet absorption method, etc. Among them, DCIP titration method is widely used, it has the advantages of simplicity, fast, more accurate, and so on, suitable for the analysis of many different types of samples. The disadvantage is that the dehydrogenated astrophic acid and the content of combined astrophic acid in the sample cannot be directly determined and are susceptible to interference from other reduced substances. If the sample contains pigment, it will make it difficult to observe the titration end point.
In acidic environments, astrochic acid (also archetype) can restore dye 2,6-DCIP to a colorless prototype
2,6-DCIP, while astrochic acid is oxidized into dehydrogenated astrochic acid. The oxidizing type 2,6-DCIP is blue in a neutral or alkaline solution, but pink in an acidic solution. Therefore, when titration of an acidic solution containing assailtic acid with 2,6-D
ICP
, the drop of 2,6-DCIP is immediately reduced to colorless before the asytic acid is fully oxidized. Once all the assailtic acid in the solution is oxidized, then drop a trace excess of 2,6-DCIP immediately so that the solution shows light pink or slightly red, this is the titration end point, indicating that the assailable acid in the solution has just been fully oxidized. Based on the consumption (ml) of the titration 2,6-DCIP standard solution, the assacleic acid content in the sample under test can be calculated. Oxidizing type 2,6-DCIP and also prototype astrophic acid are often reacted in a solution of herbic acid or partial phosphoric acid. That is, the sample is dissolved in a certain concentration of acidic solution or after pumping, and then with 2,6-DCIP standard solution titration to the end point. The reaction is as follows: