when we performed the TLC experiment, the class chose a mixture for the mobile phase of...

when we performed the TLC experiment, the class chose a mixture for the mobile phase of 80 % ethyl acetate and 20 % hexanes. why was this composition chosen

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Expert Solution

We have non polar hexane and a very highly polar ethyl acetate. The affinities of alkaloids and various other components towards an eluent are different due to the different magnitudes of dipole (or polarities) that they have. You need a right combination of hexane and ethyl acetate to ensure enough resolution of the components of a mixture and a decent rate of elution.

It is a trade off. Large quantities of hexane relative to ethyl acetate would facilitate very good separation of the components, but with very slow elution of the required alkaloid (Because the affinities of the components are not only very different, but also very low towards hexane). It is the opposite when ethyl acetate is used. The elution is fast, the resolution is low and you may still get back a mixture of alkaloid and other components (Because the affinities of the components are closer and much higher towards ethyl acetate).

queen_honey_blossom answered 1 year ago

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