A substance with a partition coefficient of 2.0 is extracted into an organic pha

Question

A substance with a partition coefficient of 2.0 is extracted into an organic phase by successively using 4 equal volumes. If the initial aqueous solution was 50 mL, how much organic solvent (total) would be needed to extract 95% of the substance? Report your answer in mL.

Compounds A and B elute from a chromatographic column after 10 and 18 minutes, respectively. The time required for the mobile phase to pass through the column is 5 minutes. Calculate the separation factor for substances A and B.

Explanation / Answer

With partition coefficient = 2

amount extracted 95%

remaining in aqueous pahse = 5%

let x be the volume of organic solvent

5 = [1/(2(x/50) + 1)]^4

taking log on both sides

5 = [1/(0.04x + 1)]^4

1.495 = 25/x + 1

0.495 = 25/x

volume of organic solvent needed (x) = 50.50 ml

Fo the chromatographic run,

searation factor for A and B = k

= (18 - 5)/(10 - 5)

= 2.6

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