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Composition of tomatoes and tomato products in antioxidants (WG1) page 91
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Apparatus: Flasks 200ml
Pipettes 2 ml
Burette 50 ml
Burette 25ml precision 1/20
Preparation of titrated solution of 2,6 dichlorphenolindophenol :
0.1 g of 2,6 dichlorphenolindophenol are diluted in distilled water, then filtered and
diluted to 200 ml. 0.1 g of pure L-ascorbic acid weighed precisely and dissolved with 100 ml
of solution made of metaphosphoric acid 3% and acetic acid 8% (already prepared).
2 ml of standard solution are transferred in a 50 ml flask and suddenly titrated with the
2,6 dichlorphenolindophenol solution until a mild pink color remain for 5 seconds.
From the media (A) of 3 of these titrations it is possible to calculate the concentration
of 2,6 dichlorphenolindophenol solution :
2
x = --------; x = Amount of ascorbic acid titrated by 1 ml of 2,6 dichlorphenolindophenol
A
Extraction of tomato samples and determination:
50 ml of fresh tomatoes are diluted to 100ml with solution made of 3% of
metaphosphoric acid in acetic acid at 8%. Mix and filter, then 10 ml of filtered solution are
titrated with the 2,6 dichlorphenolindophenol solution until a mild pink color remain for 5
seconds.
Ascorbic acid concentration is expressed in mg/L
9.2.2.2 Determination of ascorbic acid by HPLC
Samples are analyzed with HPLC after dilution with metaphosphoric acid to have the
complete solubilization of ascorbic acid present .