For the seperation of A and B by column 2 in the photo: a. If broadening is main

Question

For the seperation of A and B by column 2 in the photo:

a. If broadening is mainly due to longitudinal diffusion, how should the flow rate be changed to improve the resolution?

b. If broadening is mainly due to the finite equilibrium time , how should the flow rate be changed to improve the resolution?

c. If broadening is mainly due to multiple flow paths, what effect will flow rate have on the resolution?

lluell sahid spreading the allu 23-32. Chromatograms of compounds A and B were obtained at the same flow rate with two columns of equal length. The value of t is 1.3 min in both cases Column 1 Column 2

Explanation / Answer

a)

If the broadening is due to longitudinal diffusion, we have to increase the flow rate to improve the resolution.

Longitudinal diffusion corresponds to diffusion across the length, means more time spent by molecules in given number of theoretical plates. We have to decrease time spent by increasing flow rate.

b)

If finite equilibrium time is causing the broadening, then we have to decrease the time. So, we have to increase the flow rate.

c)

Molecules take different paths while travelling from one end of column to another. If some molecules take more time than other then we have multiple flow path broadening.

It is quite difficult and tricky to answer this question. Relative size of molecules have a say in this type of broadening. Small particles will show no/less effect of multipath broadening but larger molecules may show some.

We can increase flow rate drastically to push the molecules further through stationary phase but resolution might get affected.

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