Astro-astic acid content determination (2,6 ichlorophenol)

, objective
to learn the physiological function and properties of vitamin C, master the principles and methods of determining vitamin C by 2, 6 ichlorophenol.
II, Principle
Vitamin C is a water-soluble vitamin, is one of the most important vitamins in human nutrition, the human body lack of vitamin C will appear ascertic disease, so it is also known as aspertic acid. Vitamin C also has the effect of preventing and treating colds and suppressing the production of carcinogens.
Vitamin C is widely distributed, especially in fruits (e.g. kiwis, oranges, lemons, hawthorns, sleeves, strawberries
, etc.) and vegetables (leeks, celery, green peppers, spinach, cucumbers, tomatoes, etc.).
different cultivation conditions, different maturity and different processing and storage methods can affect the assailable acid content of fruits and vegetables. Determining astrochmic acid content is an important index to understand the quality of fruits and vegetables and the effectiveness of their processing process.
vitamin C is highly oxidized in the presence of metal copper and assailtic acid oxidase, so vitamin C is easily lost when making food from copper products. In addition, vitamin C is easily destroyed in alkaline solutions and stable in acidic solutions. Its content can be measured by its reduced properties. Also prototype astro-astroic acid can be oxidized to dehydrogenation by dyes 2, 6- dehydrophenol, the dye in the alkaline solution is blue, in the acidic solution is red, reduced to colorless. Therefore, when the acidic solution containing vitamin C is titrated with 2,6 ichlorophenol, vitamin C is not fully oxidized, the droplet dye immediately turns the solution pink, and when all the asytic acids in the solution are oxidized into dehydrogenated astroviric acid, the dripping 2,6 chlorophenol immediately makes the solution appear light red. With this dye titration astrochmic acid to the solution is light red as the end point of titration, according to the dye consumption can be calculated in the sample also prototype astrophic acid content.
III, instruments,
reagents
and materials
1 .instrument
(1)
balance
(2)
organization
masher
(3) micro
titration tube
(5 ml)
(4)
capacity bottle
(50 ml)
(5) scale
suction Tube
(5 ml, 10 ml)
(6) conical bottle (100 ml)
2 .reagent
(1) 1% herbal acid solution: herbal acid 1g soluble in l00ml distilled water
(2) 2 % herbal acid solution: 2g herbal acid dissolved in l00ml distilled water
(3) scum acid standard solution (0. 1 mg/ml): Precisely named l0mg pure astrophic acid (should be white, if turned yellow is not available) dissolved with 1 % herbic acid solution. Set the capacity to l00ml. This solution should be stored in a brown bottle, preferably pre-use preparation.
( 4 ) 0 . 05 % 2,6 ichlorophenol solution: 500mg 2, 6- Dichlorophenol is dissolved in 300 ml of hot water containing 104 mg of sodium bicarbonate (A. R), diluted to 1000 ml with distilled water after cooling, filtered out insoluble, stored in brown bottles, 4''C refrigeration can be stabilized for a week, before use with standard assailable acid calibration.
3.material
Fresh fruit or vegetables
4, operation step
1 . Extract astroceric acid
Take fresh fruit or vegetables 50g, add 50ml 2% hertic acid solution, and beat into a smooth slurry with a tissue masher.
filter
the filter, the filter cake can be washed several times with a small amount of 2% of the grass acid, combined with the filter fluid, record the filtration liquid accumulation.
2 . 2 , 6 calibration of a chlorophenol solution
accurately absorb 4 . Oml astrophic acid standard solution (containing 0 . 4g astrophic acid) in an l00ml conical bottle, plus 16ml 1% hertic acid solution, titration to light red with 2, 6 iclophosphonol (the end point is not fading in 15 seconds). Record the volume of the dye solution used to calculate the amount of assidtic acid that the l ml dye solution can oxidize.
3 . sample titration
accurately absorb sample extract two parts, each 20 ml, respectively, into two 100 ml conical bottles, titration method with 2 operation, and take 20 ml 1 % of grass acid for blank control titration.
5, results processing
take two samples titration consumption of the average size of dyes, substitute for the next calculation of 100g samples also prototype astrophic acid content: , V 1 for titration samples consumed by the average number of milliliters of dye;
V 2 is the average number of milliliters of dye consumed for titration blank control;
V is the total product of sample extraction;
V 3 is the number of milliliters of sample extract taken at titration;
M is the amount of oxidizing asseptic acid (mg) of l ml dye (which can be calculated by operation 2); and
W is the weight of the sample to be measured (g).
6. Note
(1) Although it is easy to determine asbic acid content by this method, it has the following disadvantages: First, this method can only determine the prototype astrochic acid, can not measure oxidizing astrochic acid with the same physiological function and binding astrochic acid. Second, the pigment in the sample often interferes with the judgment of the end point, although it can be pre-colored with self-terracotta, or add 2-3 ml of dchloroethylene, with the red layer of DCH as the end point, but in fact it is still difficult for rabbits to produce errors.
( 2 ) with 2 % oxalic acid preparation extract, can effectively inhibit astrophic acid oxidase, so as not astrophic acid into an oxidizing type can not be titrated, and 1 % oxalic acid does not have this effect.
(3) if there are more ferrelide ions (Fe 2 plus) in the sample, the dye can also be reduced to affect the determination, then should be replaced by 8 % acetic acid instead of herbal acid preparation sample extract, at this time Fe 2 plus will not work with the dye very quickly.
(4) if the sample slurry foam too much, can add a few drops of cinol or butanol de-foaming.
( 5 ) commercially available 2 , 6 ichlorophenols of varying quality, to calibration 0.4 mg asseptic acid consumption of about 2 ml of dyes is appropriate, according to the calibration results can be adjusted dye solution concentration.
( 6 ) sample extraction preparation and titration process, to avoid sunlight and contact with copper, iron appliances, so as not to destroy astrophic acid.
(7) titration process should be rapid, generally not more than 2min, sample titration consumption dye 1 - 4 ml is appropriate, if beyond this range, should increase or decrease the amount of sample extraction.
extracted from the oil ( 8 ) can also be centrifugally collected if the slurry is not easily filtered.
, thinking question
1. What is the nature and physiological function of vitamin C?
2. What problems should I pay attention to in order to get accurate assachic acid content in the experiment?
, editor
Fengyao, a chinese newspaper. Vitamin fun talk. Chongqing: Sichuan Science and Technology Press, 1999
Li Jianwu, etc.
principles and methods
biochemistry and experiments. Beijing: Beijing University Press, 2001
Wenshuji Editor- Editor. Basic biochemical experiment guidance. Xi'an: Shaanxi Science and Technology Press, 1994
Strong , F . M. and Koch , G . H., Biochemistry, Laboratory Manual, WM . C. Brown Co. Publishers, Iowa, USA, 1974 .