Overloading study of ionized compounds in hydrophilic interaction chromatography

Abstract

The overloading behaviour of charged acidic (acetylsalicylic acid and nicotinic acid) and basic (creatinine and 1-ethyl-2,3-dimethylimidazolium) solutes was investigated on two stationary phases (bare silica and amidebonded silica) in the hydrophilic interaction chromatography separation mode at three mobile phase pH values (3.0, 5.0 and 7.0). On the bare silica both cationic solutes showed the increased peak tailing as the sample load increased. However, on the amide phase they exhibited a quite different overloading behaviour. The peak shapes for creatinine showed the increased tailing whereas for 1-ethyl-2,3-dimethylimidazolium peak fronting occurs with the sample load. Anionic solutes on both phases showed the increased peak fronting as the sample load increased. In neutral and slightly acidic mobile phases the loadability of the bare silica phase was much higher for bases than for acids. In addition, the loading capacity for the bases increases with pH whereas an opposite trend was observed for the acidic compounds. The amide phase gave similar loading capacity values for both types of solutes and its loadability is less sensitive to pH changes, compared to that of bare silica. The obtained results indicate that ionic interactions with dissociated surface silanols play an important role in the overloading behaviour of charged solutes.