Amitriptyline peak becomes a tailing peak by influence of residual silanol groups and many HPLC manufacturers use amitriptyline as an index of the amount of silanol groups. We evaluated the amount of residual using amitriptyline.
It is generally known that a peak tailing for a basic compound occurs more using acetonitrile in the mobile phase than using methanol although methanol has been used as an organic solvent in the mobile phase for separating basic compounds.
Sunniest C18, RP-AQUA, C8 showed sharp peaks without tailing even with acetonitrile. In other words, the Sunniest C18, RP-AQUA, C8 column, without the use of organic solvent is limited, can be set to a wide range of mobile phase conditions, you can construct an optimum separation conditions for all of the components.