You will need a metric ruler (NOT inches). First state the equation that gives t

Question

You will need a metric ruler (NOT inches). First state the equation that gives the retention factor Rf. Next, for spots "X", "Y" and "Z" in the chromatogram below, calculate the R_f. This will involve taking measurements directly off the chromatogram. You may find page 7 of the Paper Chromatography v. 10 technical guide helpful. Control all sig figs! Four pure substances (each has a different color: blue, yellow, orange and red) and a mixture of all four are run with five different mobile phases by paper chromatography; pure solvent "A", pure solvent "B", and various mixtures of solvent "A" and "B" as indicated in the diagrams below. The paper chromatography was carried out as per the Paper Chromatography v.10 technical guide. Carefully study the results. There are three things to consider: 1) the sharper (less spread-out) the spot the better, 2) the "center of mass" height of each spot should be different - the greater the difference the better, and 3), the development time. You don't have timing information, so based on 1) and 2) what is the best mobile phase that resolves all four substances?

Explanation / Answer

1) Retention factor is give as R(f) = a/b

a : distance from the origin Z, to the center of the respective spot (either X or Y)

b: distance from the origin Z, to the solvent front

For spot X: R(f) = 1.9 cm/5.3 cm = 0.36; approx = 0.4

For spot Y : R(f) = 3.1 cm/5.3 cm = 0.58; approx = 0.6

2) The best mobile phase is 3:1 (75/25) A:B

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