A student researcher performed a chromatographic separation of caffeine and aspartame with methanol as the mobile...

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Chemistry

A student researcher performed a chromatographic separation ofcaffeine and aspartame with methanol as the mobile phase using aCâ€“18 column. The retention times for methanol (tm) , caffeine (tc), and aspartame (ta) were 41.8 s , 96.3 s , and 143.8 s ,respectively.
What is the selectivity factor (relative retention), Î± , forthis column?
Î±=
Calculate the hypothetical retention times for caffeine andaspartame if their retention factors were reduced by 28.0% . Assumethe mobile phase retention time (tm=41.8 s) remains constant.
tcaffeine=
staspartame=
Select the statements that correctly describe the outcome if thepartition coefficient for caffeine (Kc) were to decrease.
The retention time of caffeine would increase.
The retention time of caffeine would decrease.
Caffeine would spend a greater amount of time in the mobilephase.
The retention factor of caffeine would decrease.
The retention factor of caffeine would increase.
The retention time and retention factor of caffeine would notchange.

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Solution What is the selectivity factor relative retention for this column Selectivity factor The ability of chromatographic system to chemically distinguish between two components of the sample It can be determined by following formula Selectivity factor tR2 t0 tR1 t0 Where tR2 Retention time of component 2 tR1 Retention time of component 1 and t0 A nonretained compound has no affinity for the stationary phase and elutes with the solvent front at a time t0 which is also known as the holdup time or dead time We have all the information to determine the Selectivity factor tR2 ta Retention time of aspartame 1438 s tR1 tc Retention time of caffeine 963 s t0 tm retention time of MeOH 418 s See Answer

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