The question is below the plot. Following plots (van Deemter) are obtained on 3

Question

The question is below the plot.

Following plots (van Deemter) are obtained on 3 identical columns packed with the same material as a stationary phase. Assume that the only difference in these columns are varying (packing-material's) particle size. a) Assume that all the experimental conditions are the same (the same flow rate, the same mobile phase etc.), which column is expected to perform best and which one is worst in terms of resolution while separating 2 similar analyses? Justify your answer.

Explanation / Answer

Step I

Lets start with assuming a fixed flow rate in the plot i.e., 4 mL/min.

Step II

Write the respective plate height for this flow rate for different particle sizes -

3 microm, H = 5 microm

5 microm, H = 15 microm

10 microm, H = 35 microm

Step III

Plate height is given as -

H = L / N where N is the number of theoretical plates and L is the length column.

So, N = L / H

If we keep the length of column to be same for all cases, we can see from above equation that with increasing H, N decreases.

Step IV

And N is proportional to resolution. That means Resolution is inversely proportional to H.

So, 10 microm particle column will have the lowest resolution (worst) and 3 microm particle column will have the highest resolution (best).

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