Primesep B has been applied to the analysis of amitriptyline. Amitriptyline is a tertiary amine commonly used a probe in reversed-phase columns to test silanol activity. On C18 phases amitriptyline often tails unless mobile phase modifiers such as triethylamine or high ionic strength buffers are used. Primesep B has an embedded cation which shields the silica by ionic repulsion with the amitriptyline cation. Excellent peak shape results with a mass spec compatible mobile phase of water, acetonitrile (MeCN, ACN) and trifluoracetic acid (TFA).