Primesep B separates tertiary amines, such as cetylpyridinium with symmetrical peak shape by a combination of reversed-phase and ion-exclusion mechanisms. The embedded basic functional group on the stationary phase shields the underlying silanols to prevent peak tailing. Retention time can be changed by changing either organic content or acid content in the mobile phase. C18 reversed-phase columns do not typically show this tuning ability with acid content. Excellent peak shape results with a mass spec compatible mobile phase of water, acetonitrile (MeCN, ACN) and trifluoracetic acid (TFA) with UV detection at 250 nm.