Our original mixed-mode columns. Every Primesep column has a dual-chemistry stationary phase with a hydrophobic long alkyl chain and an ionizable cationic or anionic embedded group. When the polar group bears a charge, it effectively shields any less-polar groups of the stationary phase. As a result, silanol groups, which cause unwanted interaction in many reverse-phase columns, are completely undetectable and do not affect the peak shape and selectivity.