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Capacity Factor Problem

Question: Two analytes A and B, have retention times of 13.5 min and 19.5 min, with peak widths of 2 min and 2.8 min for a mobile phase composition of 20% methanol and 80% H2O, on a 15 cm C18 column which has a dead time of 1.5 min. Determine the composition of methanol and H2O at which the capacity factor for A becomes 2. What is the capacity factor of B at this new composition?

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I had to use some extra information to solve the following problem. I hope that is okay. It is imperative otherwise the problem cannot be solved.

Well we know that the Vo or the dead volume does not change with volume composition, and so Vo or t0 = 1.5min always. As for tA and tB they do change.

We know that the k'A1=(13.5-1.5)/1.5=8 ...

Solution Summary

This solution is comprised of a step-by-step guide of how to work through the following calculation based problem. Rationale behind some of the steps is also provided. The solution is about 230 words.