7. (a) When you try separating an unknown mixture by reversed-phase chromatograp

Question

7. (a) When you try separating an unknown mixture by reversed-phase chromatography with 50% acetonitrile/50% water, the peaks are too close together and are eluted in the range k = 2-6. Should you use a higher or lower concentration of acetonitrile in the next run? (b) When you try separating an unknown mixture by normal-phase chromatography with 50% hexane/50% methyl t-butyl ether the peaks are too close together and eluted in the range k = 2-6. Should you use a higher or lower concentration of hexane in the next run? 7. (a) When you try separating an unknown mixture by reversed-phase chromatography with 50% acetonitrile 50% water, the peaks are too close together and are eluted in the range k 2-6. Should you use a higher or lower concentration of acetonitrile in the next run? (b) When you try separating an unknown mixture by normal phase chromatography with 50% hexane/50% methyl t-butyl cther the pcaks are too closc together and clutcd in the range k 2-6. Should you usc a higher or lower concentration of hexane in the next run

Explanation / Answer

7.

(a) water is more polar than acetonitrile.

To improve the separation between the peaks we must increase the percentage of acetonitrile (non-polar) component in the eluting solvent. this would allow for the components to stay at the column for longer time and better separation would be seen.

(b) hexane is more less polar than methyl t-butyl ether.

In normal phase chromatography, to improve separation between the peaks we would increase the concentration of hexane in the eluting solvent. This would allow for component sto sepnd more time on column and thus better separation between them would be obtained.

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