Sample self-stacking in capillary zone electrophoresis: behavior of samples containing multiple major coionic...

It is a frequent phenomenon in practice that a sample contains bulk levels of more than one coionic component that affect the stacking behavior of minor analytes and in this way also the sensitivity of the method. Here, attention is paid to stacking resulting from the presence of a macrocomponent of leading type that is deteriorated by the presence of another macrocomponent of like charge in the sample. Based on the isotachophoretic model of migration in the initial period of separation, a theoretical approach was elaborated both for strong and weak electrolytes which describes the separation process and finds the conditions that define whether transient isotachophoretic stacking of the analyte takes place or not. It is shown that the crucial parameter is the ratio of the concentrations of macrocomponents migrating in front and behind the analyte of interest. The destacking effect can also be expected when the coion of the background electrolyte is present in the sample. Rules how to cope with effects of destackers present in the sample are given. Theoretical considerations are illustrated by computer simulations and verified experimentally. Examples of antagonistic effects of macrocomponents are demonstrated for model serum samples.