(a) When you try separating an unknown mixture by reversedphase 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 pure 50% hexane/50% methyl t-butyl ether, the peaks are too close together and are eluted in the range k = 2-6. Should you use a higher or lower concentration of hexane in the next run?