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Author Topic: ESTIMATION OF ASCORBIC ACID  (Read 11713 times)
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Francis Umeoguaju
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« on: April 10, 2010, 08:58:16 am »


Ascorbic acid is oxidized by the blue coloured dye, 2,6-dichlorophenolindophenol
to dehydroascorbic acid; at the same time, the dye is reduced to a colourless compound so that the end point of the reaction can be easily determined.

REAGENTS AND PREPARATIONS
   2,6-dichlorophenolindophenol, (3.2g of the dye was dissolved in about 40ml of hot  water, this is cooled and made up to 50ml with distilled  water)
   
   20mg/1000ml solution of standard vitamin C is prepared just before use
   
   Diluted sample that have vitamin C concentration of about 0.1mg.
   
   Glacial acetic acid

PROCEDURE

   5ml of the sample is mixed with 1ml of glacial acetic acid, the mixture is then titrated with the dye solution until the blue dye changes to a permanent pick colour. The titre value is noted. Strove et al suggests an end point of a pink colour that remains visible within 30 seconds.
   
   The titration is repeated with 5ml of water for the Blank 5ml ascorbic acid standard solution. The vitamin C content of the sample is calculated as follows:
   
Vit. C of test (mg/100ml)= ((T-Blank) X 2 X dilution)/
              (St-Blank)

Where
T-Titre of samples
St= standard

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