Modern C18 columns have very similar selectivity, even for basic compounds, because silica quality and bonding techniques have improved to the point that silanol effects are minimal. Unless quality with your current column is the issue, the main reasons for evaluating different brands of C18 columns are for improved peak shape and for slight changes in selectivity. - See more at: http://www.sigmaaldrich.com/analytical-chromatography/hplc/columns/ascentis-hplc-columns/c18.html#sthash.GxugtRnI.dpuf