[teflon66]

In this experiment, I had to separate a mixture of salicylic acid and triphenylmethanol with column chromatography using a 60:40 ratio of ethyl acetate to hexane. We collected 2 mL of the eluent in 7 vials. Then, we ran the fractions against authentic triphenylmethanol and salicylic acid using thin-line chromatography. We converted each distances of the spots on the TLC plate to Rf values. 4 TLC plates were used, with two fractions and authentic salicylic acid and triphenylmethanol on each.

Here's what I got:

TLC Plate #1: Fraction 1 = 0.940, Fraction 2 = 0.910, Authentic S.A. = 0.820, Authentic Tri. = 0.920

TLC Plate #2: Fraction 3 = 0.960, Fraction 4 = No spot appeared, Authentic S.A. = 0.850, Authentic Tri. = 0.930

TLC Plate #3: Fraction 5 = No spot appeared, Fraction 6 = No spot appeared, Authentic S.A. = 0.780, Authentic Tri. = 0.880

TLC Plate #4: Fraction 7 = No spot appeared, Authentic S.A. = 0.780, Authentic Tri. = 0.860



I'm confused at how to interpret these results. The first 3 fractions' Rf values are similar to the authentic triphenylmethanol Rf values, so I was able to separate the mixture and collect triphenylmethanol. But, after fraction 3, no spots appeared on the TLC plate: Does this mean that the mixture wasn't separated? Why is that the case?

Any help would be much appreciated!

[OrganicDan96]

what are the key differences between the two compounds, how would they differ on the column?

[hollytara]

PS  TLC = Thin Layer Chromatography

Did you see two spots in your fractions?

One problem is you did not run the TPM and SA as a mixture to see if two spots appeared from the mixture.

Are you sure everything had eluted from the column when you finished?

[Babcock_Hall]

Your R_f values are higher than one sometimes sees.  Was this intentional?  How large were your spots?