$($a$)$ The following chromatograms $($Figure $1)$ were produced by analysis of a mixture of $9$ polyaromatic hydrocarbons using a $15cm$ phenyl$-$hexyl column $($top$)$ or a $15cmC$; ${?}_8$ column $($bottom$),$ and gradient elution as follows:

$\backslash$table$[[$time $($min$),\%$A $($water$),\%$B $($methanol$)],[0,90,10],[2,90,10],[10,0,100],[11,0,100]]$

$($i$)$ What type of gradient was used in this experiment? Draw a schematic representation to justify your answer.

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Question $1$ Cont'd Overleaf

Page $2$ of $7$

CHM$7001$

May $2023$

$($ii$)$ Describe the quality of each chromatogram in Figure $1$ and propose which of the two tested columns should be used for this separation. Justify your answer by discussing the type of interactions between the sample components and the stationary phase in each case.

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