Asymmetry, peak secondary interactions

In this section, we will deal with the major contributions to the asymmetry of peaks. We will first deal with asymmetry due to overloading, and then we will deal with asymmetry due to secondary interactions. 

Band tailing leads inferior separations and reduced precision. Thus, conditions resulting in tailing or asymmetrical peaks should be avoided. Peak asymmetry or band tailing can arise from several sources plugged column frits, void in the column, buildup of garbage on the column inlet, sample overload, solvent mismatch with sample, chemical or secondary interaction (many times silanol effects). 

In comparing the various test procedures, there is always a good agreement found for hydrophobic retention and selectivity as well as for shape selectivity. However, the characterization of silanophilic interaction is still a matter of discussion. In part, the differences are due to the selection of the basic analyte. Therefore, the outcome of every test is different. It has been shown, that the peak asymmetry—used for detection of silanophilic interactions—does not correlate to the pA" value of the basic test solute [64]. A closer look at these data leads to the assumption, that the differences are related to the structure of the basic solute, irrespective of whether a primary, secondary, or a tertiary amine is used. The presence of NH bonds seems to be more important in stationary-phase differentiation than the basicity expressed by the pA value. For comparable test procedures for silanophilic interactions further studies seem to be required. 

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