Open and Toroidal Electrophoresis. Tarso B. Ledur Kist

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as a function of pH and Figure 1.9 for a 0.1 M glycyl-aspartic acid. Note that both images-alanine and glycyl-aspartic acid do have isoelectric points (IEP), however only glycyl-aspartic acid has a good buffer capacity around its or close to the pH(I). A high buffer capacity at or close to the pH(I) is a highly desired property in the ESTs, as it allows the pH to be stabilized with minimal increase in the conductivity.

      The total conductivity of the buffer must be higher than or close to the conductivity of the sample, otherwise it causes band destacking (Section 2.14). On the other hand, the lower the conductivity of the buffering electrolyte to the total conductivity of the buffer solution the better, as some room is left for the addition of some electrolytes with the same mobility as the analytes. This is important for the production of symmetric peaks in most of the separation modes. Isotachophoresis and isoelectric focusing are exceptions to this rule as they are based on special separation mechanisms. Some samples do have low conductivities, in this case the development of buffer solutions with low conductivity, i.e. designed for high field strengths operations, is always an active topic of research, [12] as they lead to high separation efficiencies (Section 3.5).

Grid chart depicting the buffer capacity of 0.1 M glycyl-aspartic acid (pKa = 2.81, 4.45 and 8.6) in an aqueous solution. Note the high buffer capacity at pH(I) = 3.6.
, 4.45 and 8.6) in an aqueous solution. Note the high buffer capacity at images.

      Another very useful concept is the normalized buffering capacity/conductivity ratio.[13] Here, the buffering capacity at each pH is divided by the buffer conductivity at this pH. A high buffer capacity and low buffer conductivity are highly desirable. This allows different buffers to be compared among themselves at different pHs. Such performance rankings of good buffers are still missing in the literature.

      Finally, there are a few applications (for instance the separation of aminium ions, quaternary ammonium ions, and coordination complexes) that can be run with pure propylene carbonate, formamide or other solvents, since the analytes remain charged within them. Moreover, propylene carbonate, for instance, does not produce gases at the electrodes, allowing the separation to be run in sealed systems.

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      11 11 Gagliardi, L.G., Tascon, M., and Castells, C.B. (2015). Analytica Chimica Acta 889: 35–37.

      12 12 Hjertén, S., Valtcheva, L., Elenbring, K., and Liao, J.L. (1995). Electrophoresis 16: 584–594.

      13 13 Stoyanov, A.V. and Righetti, P.G. (1998). Electrophoresis. 19: 1674–1676.

      14 14 Schwer, C. and Kenndler, E. (1991). Analytical Chemistry 63: 1801–1807.

      15 15 Sarmini, K. and Kenndler, E. (1997). Journal of Chromatography A 792: 3–11.

      16 16 Sarmini, K. and Kenndler, E. (1998). Journal of Chromatography A 606: 325–335.

      17 17 Sarmini, K. and Kenndler, E. (1998). Journal of Chromatography A 811: 201–209.

      18 18 Sarmini, K. and Kenndler, E. (1998). Journal of Chromatography A 818: 209–215.

      19 19 Sarmini, K. and Kenndler, E. (1999). Journal of Chromatography A 833: 245–259.

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