Food Science
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I am investigating the effect of cooking on the vitamin C content of cabbage. My problem appeared when I had to calculate the dye factor. Can you please tell me step-by-step what I have to do?
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Igloo writes ....
When you are titrating vitamin C solutions of unknown concentration against DCPIP (2,6-dichlorophenolindophenol) dye, you first need to standardise the dye solution against a standard solution of vitamin, i.e. against one of known concentration.
Using a pipette you first transfer a known volume of the standard vitamin C solution into a conical flask and then titrate with the dye solution until the solution turns to a permanently faint pink colour. This is the end-point.
The "dye factor" is a concept designed to make subsequent calculations straightforward and gives a measure of the concentration of the dye solution. It is defined as the number of mg of vitamin C which exactly react with 1 cm3 of the dye solution.
Let us assume that the concentration of your standard vitamin C solution is Z mg dm-3, that you used VvitC cm3 of vit. C solution (from the pipette) and that the dye titre was Vdye cm3.
The mass of vitamin C used for each titration must therefore have been Z x VvitC/1000 mg. Vdye cm3 of dye were needed to react with this, so 1 cm3 of dye would have needed (Z x VvitC /1000) /Vdye mg of vitamin C, and this, of course, is the dye factor.
Thus, rearranging, the dye factor = Z x VvitC/1000Vdye.
Let's assume that your standard vitamin C has a concentration of 200 mg dm-3 and that you used a pipette of volume 25 cm3, and that the volume of dye needed was 20 cm3.
In this case the dye factor would be (200 x 25)/(1000 x 20) = 0.25 mg cm-3.
Titrations can now be carried out with the same dye solution and solutions of vitamin C of unknown concentrations, using the dye factor to deduce their concentrations. In your case this is where your cabbage extracts come in.
Since your question specifically referred to the determination of the dye factor, I presume that you now know what to do to carry out all the subsequent calculations.
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updated: 28 July 2008
