a) nonpolar aromatic compounds were separated by hplc on a bonded phase containing octadecyl groups [—(ch2)17ch3] covalently attached to silica. eluent was 65 vol% methanol in water. how would retention times be affected if 90% methanol were used instead? (b) polar solutes were separated by hplc (not hilic) with a bonded phase containing polar diol substituents [—ch(oh)ch2oh]. how would retention times be affected if eluent were changed from 40 vol% to 60 vol% acetonitrile in water? acetonitrile (ch3cqn) is less polar than water. (c) polar solutes were separated by hydrophilic interaction chromatography (hilic) with a strongly polar bonded phase. how would retention times be affected if eluent were changed from 80 vol% to 90 vol% acetonitrile in water? (d) polar solutes were separated by normal-phase chromatog- raphy on bare silica, using methyl t-butyl ether and 2-propanol solvent. how would retention times be affected if eluent were changed from 40 vol% to 60 vol% 2-propanol? (hint: see table 22-2.)