[Dolphinsiu]

In my experiment,

1.Turn on the fluorometer and allow it to warm up.

2.Prepare six solutions.

Solution   Soy milk    Riboflavin(10 ppm)   Water    Anhy. CaSO4
  (1)         20 ml            0 ml                 25 ml           5 g
  (2)         20 ml            5 ml                 20 ml           5 g
  (3)         20 ml            10 ml               15 ml           5 g
  (4)         20 ml            15 ml               10 ml           5 g
  (5)         20 ml            20 ml                5 ml            5 g   
  (6)         20 ml            25 ml                0 ml            5 g

3.Heat each solution gently until precipitation is completed. Cool and clear the filtrate by certrifugation. Then measure the fluorscence reading of filtrate in the above six solutions.

4.By ploting fluoroscence readings against the concentration of riboflavin. We can know the content of riboflavin by extrapolating the standard addition method.

I get stuck when I met this question.

Q. Why was the riboflavin added to the soy milk before the CaSO4 precipitation and not after?

My attempted thinking:

CaSO4 is used to precipitate the protein in soy milk upon gentle heat. If riboflavin is added before, then this can minimize the temperature difference between riboflavin added and that in soy milk which causes error in fluorometric measurement. In addition, this can prevent the redissolution of the preciptate in newly-added riboflavin. If so, protein and CaSO4 decomposes and these two components will count to the unwanted error on the measurement.

Am I right? If anyone have different idea, welcome to raise it and learn from each other!

[Dolphinsiu]

Really no one have done this experiment before ?