(a) Methanol is less polar thn water.
If we were to replace the eluting solvent from 65% MeOH in water to 90% MeOH in water, we are reducing the polarity of the eluting solvent, thus the non-polar components woudl stay n the non-polar stationary phase for longer periods. The retention times gets longer.
(b) octanoic acid is more polar than aminooctane.
With 20% MeOH in water, the solvent is more polar and would elute octanoic acid first from the column at pH 3 as more polar solvent dissolves more polar component preferentially.
(c) acetonitrile is less polar than water so increasing the solvent from 80% to 90% acetonitrile in water as eluent, would make the solvent less plar and thus non-polar compounds would slute first from the column.
Retention time woud increase.
(d) Propanol is more polar than ether.
Changing the solvent from 40% to 60% propanol would increase polarity of the eluting solvent. So less polar compounds would elute faster in such a solvent while decreasing the reatention time for polar components.
25-17. (a) Nonpolar aromatic compounds were separated by HPLC on an octadecyl (CD bonded phase. The...