Peak tailing phenomena

Kiel et al. [1450], studied the effect of the presence and absence of an amine buffer and solvent pH on the retention and tailing of nortriptyline, desmethylnor-triptyline, and amitriptyline. A Cg column and a 50/50 acetonitrile/water (25 mM TEA) solvent gave baseline resolution, excellent peak shape, and elution within 4 rnin. Removal of the TEA led to significant peak tailing and an elution time of nearly 7 min. With no TEA, the mobile phase was buffered to different pH values (2.5-8) with 0.1M phosphate. A U-shaped plot of k versus pH resulted. This phenomenon was not because of a protonated-to-deprotonated form of the amine compounds, their piif, values are >8. Rather, it is due to surface silanol acidity functions and the complex interaction of the solutes with these sites. Therefore, it is important to consider the use of a basic mobile phase modifier when analyzing basic compounds. 

Any use of MIP HPLC columns carries the burden of unusually wide and tailing peaks. These features are most obvious with the template itself but other analytes also show it quite often. Many explanations have been proposed to explain this phenomenon, including the following ... 

Our impression has been that unclear interpretations of the tailing peaks on MIP columns have slowed down the development of the field. It is of course a question whether, with a better understanding of this phenomenon, one can find more real-life applications for MIPs. 

Band broadening and/or unusual retention are also known to occur when specific interactions take place between particular solutes and the stationary phase. The most common cause of such band broadening is a stationary phase overload. It can be also an exclusion phenomenon due to the small size of the stationary phase pores and the large size of the solute. Acid-base interactions between the surface silanols and basic compounds, especially the amine compounds, dramatically broaden the corresponding peaks. Peak deformations, either frontings or tailings, are observed. 

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