Measurement of vitamin C content

Summary

Vitamin C is one of the most important vitamins in human nutrition and a deficiency can lead to scurvy. Fruits and vegetables are the main source of vitamin C for humans. Measurement of vitamin C content gives an indication of the quality of the fruit.

Principle

Using the dye 2,6-dichlorophenol indophenol as an oxidizing agent, the reduced state of vitamin C can be oxidized to dehydrovitamin C, while the dye itself is reduced to a colorless derivative.2,6-Dichlorophenol starch appears red under acidic conditions. Immediately before the end point of the titration, the drop of 2,6-dichlorophenol starch is reduced to colorless. The end point of the titration is when the solution changes from colorless to red.

Appliance

Commonly used in the identification of high and low fruit quality.

Operation method

Experiment for the determination of vitamin C content

Principle

Using the dye 2,6-dichlorophenol indophenol as an oxidizing agent, the reduced state of vitamin C can be oxidized to dehydrovitamin C, while the dye itself is reduced to a colorless derivative.2,6-Dichlorophenol starch appears red under acidic conditions. Immediately before the end point of the titration, the drop of 2,6-dichlorophenol starch is reduced to colorless. The end point of the titration is when the solution changes from colorless to red.

Move

I. Reagents

1. Experimental materials: fruits or vegetables.

2. Apparatus: (1) Microburette; 500 ml × 1; (2) Measuring flask: 50 ml × 2; (3) Triangular flask; 500 ml × 2; (4) Mortar and pestle; (5) Measuring cylinder; (6) Graduated pipette; 10 ml × 2;

3. Reagents:

(1) 1% oxalic acid: weigh 5.0 g of oxalic acid dissolved in a small amount of distilled water, and condense to 500 ml.

(2) 2% oxalic acid: weigh 10.0 g of oxalic acid dissolved in a small amount of distilled water, volume to 500 ml.

(3) 0.001N 2,6-dichlorophenol indophenol sodium solution: weigh 60 mg of dry 2,6-dichlorophenol indophenol sodium into a 200 ml measuring flask, heat 100-150 ml in distilled water, add 4-5 drops of 0.01N NaOH, shake strongly for 10 minutes to cool down and then add water to the scale. After shaking well, filter with tight filter paper in a brown bottle, stored in the refrigerator for backup, valid for one week. Calibration is required before use (see note).

Experimental procedure

1. Sample handling and extraction:

4.0 g of fresh sample was weighed into a mortar, 5 ml of 2% oxalic acid was added and homogenized. The sample extract was transferred to a 50 ml measuring flask through a funnel. The residue is then extracted 2-3 times with 2% oxalic acid, and the extract and residue are transferred together into a measuring flask.The total amount of 2% oxalic acid is 35 ml, and the solution is finally fixed in water. If the solution is more foam, add a few drops of ethanol to eliminate the foam and then fixed. Shake well, filter, filtrate spare.

2. Determination of the sample:

Pipette 10 ml of the filtrate into a 50 ml triangular flask and titrate immediately with sodium 2,6-dichlorophenol indophenol solution until a distinct red color appears and does not disappear within 15 seconds. The volume of titrant used was recorded.

3. Blank determination:

In another 50 ml triangular flask, put 35 ml of 2% oxalic acid and dissolve it with 1% oxalic acid, shake well, take 10 ml of this solution into another 50 ml triangular flask and titrate with 2,6-dichlorophenol sodium indophenol to the end point and record the amount of dye used.



X: mg of vitamin C contained in 100 g of sample (mg/100 g)

W: weight of sample weighed (g)

V1: ml of dye used to titrate the sample

V2: ml of dye used for titrating the blank

V: Total volume of sample extract diluted (i.e. 50 ml)

K: the number of milligrams of vitamin C that can be oxidized by 1 ml of dye solution, which can be calculated from the calibration.

Caveat

mso-bidi-language:AR-SA">Calibration of dichlorophenol indophenol sodium solution: accurately weigh the vitaminC20mg, calibrate with1% of vitamin Coxalic acid, dissolve with 1% oxalic acid to200ml. Aspirate this solution10mL of this solution was dissolved in1% oxalic acidOxalic acid was diluted again and fixed to200ml. Pipette this solution10ml of this solution into50ml triangular flask (also pipette10 ml of this solution into a 50 ml triangular flask (while aspiratingml1% oxalic acidoxalic acid in another50 ml.ml triangular flask and make a blank control immediately with the desired calibration of the2The6-Sodium dichlorophenol indophenol titration until pink color appears15secondsdisappearRecord the number of milliliters used and calculate according to the following formulaKvalue (i.e.1mg of ascorbic acid oxidized by 1 ml of dye).(Where: G is the number of milligrams of vitamin C weighed. V is the difference between the number of milliliters of de-dye used in the titration of 10 ml of standard vitamin C and the number of milliliters used in the titration of a blank.)2. the operation should be as fast as possible and prevent contact with iron and copper utensils to minimize oxidation of vitamin C.3. avoid direct sunlight on oxalic acid and sample extracts.4. when the sample solution itself is colored, add 2-3 ml of dichloroethane to the extraction solution before determination. The end point is reached when the dichloroethane changes from colorless to pink during the titration.

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