Question

A student researcher performed a chromatographic separation of caffeine and aspartame with methanol as the mobile phase using a C–18 column. The retention times for methanol ( t m ) , caffeine ( t c ) , and aspartame ( t a ) were 35.9 s , 103.5 s , and 179.6 s , respectively.

What is the selectivity factor (relative retention), α , for this column?

Calculate the hypothetical retention times for caffeine and aspartame if their retention factors were reduced by 27.0 % . Assume the mobile phase retention time ( t m = 35.9 s) remains constant.

t caffeine =

t aspartame =

Select the statements that correctly describe the outcome if the partition coefficient for caffeine ( K c ) were to decrease.

A. The retention time and retention factor of caffeine would not change.

B.The retention time of caffeine would increase.

C.The retention factor of caffeine would increase.

D.The retention factor of caffeine would decrease.

E.The retention time of caffeine would decrease.

F.Caffeine would spend a greater amount of time in the mobile phase.

Answer 1