Comparative study of divalent metals and amines as silanol-blocking agents in reversed-phase liquid chromatography.

In this work we compare the silanol-blocking ability of different alkaline earth metal cations, including calcium, magnesium and barium, and strong amine silanol blockers, such as triethylamine and octylamine, using six basic probe solutes at pH 7 on a conventional octadecylsilane phase. Some amines are better blocking agents than the metal cations but this varies with the amine and analyte structure. Among the metals, barium is the best blocker. For certain solutes barium is as effective at blocking silanols as some of the amine blockers. It produces short retention times and good peak shapes with satisfactory peak symmetry factors. However, amines with long alkyl chains, such as octylamine, are better blocking agents than barium. Peak symmetry is still poor for some solutes even in the presence of the strongest blocking agent in the eluent.