Pseudo‐Isotachophoresis Stacking: I. Investigating the Early Steps

Pseudo ITP (p-ITP) is a simple method for concentration directly on the capillary, especially for samples containing high levels of salts or proteins. By moving the sample closer to the window after injection, we investigated the early steps of stacking without the influence of the separation step (the separation buffer). About one third of the capillary was filled with the sample in the presence of salts and acetonitrile. Salts such as chromate ions moved fast as leading ions, not as a sharp peak but as a wide wave; one side of it having a high ultra-violet absorbency while the other side does not. The width of the wave is related to the salt concentration. Behind the salts, the anionic analytes moved rapidly forming sharp peak(s). As the concentration of the chromate ions are increased better stacking occurred. In the absence of salts or acetonitrile the wave did not form and the stacking was greatly diminished. Unexpectedly, the stacking was also accompanied by some separation, which was affected by the presence of buffers in the sample. This simple approach is useful for investigating other types of stacking.