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In our previous papers we have investigated the influence of the mobile phase composition on mechanism of retention, selectivity and efficiency of peptide separation in various high-performance thin-layer chromatography (HPTLC) systems with commercially available silica-based adsorbents. We have also investigated the influence of pH of the mobile phase buffer on migration and separation of peptides in pressurized planar electrochromatography (PPEC). Here we investigate the influence of concentration of ion-pairing additive, and concentration and type of organic modifier of the mobile phase on migration of peptides in PPEC system with octadecyl silica-based adsorbent, and with the same set of the solutes as before. We compare our current results with the results obtained before for similar HPTLC and PPEC systems, and discuss the influence of particular variables on retention, electrophoretic mobility of solutes and electroosmotic flow of the mobile phase. We show, that the final selectivity of peptide separation results from co-influence of all the three factors mentioned. Concentration of organic modifier of the mobile phase, as well as concentration of ion-pairing additive, affect the retention, the electrophoretic mobility, and the electroosmotic flow simultaneously. This makes independent optimization of these factors rather difficult. Anyway PPEC offers much faster separation of peptides with quite different selectivity, in comparison to HPTLC, with similar adsorbents and similar mobile phase composition. However, we also present and discuss the issue of extensive tailing of peptide zones in the PPEC in comparison to similar HPTLC systems. [ABSTRACT FROM AUTHOR]

In our paper we investigate the influence of pH of the mobile phase buffer, on retention of peptides in both: normal phase (NP) and reversed phase (RP) high-performance thin-layer chromatography systems (HPTLC), using C18 silica-based adsorbent. We also compare the influence of pH on retention and/or migration distance of peptides in separation systems of HPTLC and PPEC (pressurized planar electrochromatography) techniques. Our results show, that the change of pH of the mobile phase buffer can be used for two-dimensional HPTLC separation of peptides, but much stronger change of separation selectivity can be obtained by overall inversion of separation system type (NP/RP), as we have described before (Gwarda et al., 2016). In PPEC influence of the mobile phase pH on selectivity of peptide separation is very clear and strictly different than that in HPTLC (including overall inversion of direction of solutes migration), what results from the significant share of electrophoretic effect in overall mechanism of separation. Migration of peptides in two opposite directions results in better selectivity of separation by PPEC. In separation systems of both HPTLC and PPEC techniques, the change of pH clearly affects the efficiency of the separation system, so it can be used for optimization of separation conditions. Our results also show, that some modifications of PPEC equipment and materials could be useful for application of this technique in the field of peptide analysis. [ABSTRACT FROM AUTHOR]