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  • Author or Editor: Aneta Hałka-Grysińska x
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Satisfactory separation of a test mixture of 19 dyes with a general elution problem was obtained by reversed-phase stepwise gradient thin-layer chromatography with single void volume of the mobile phase. An effect of the supplementary mobile phase flux to the surface of the adsorbent layer, observed previously, was eliminated. This improves the flow profile of the mobile phase and the shape of spots, and increases the repeatability of the results within the same plate and between studies. The experimental values of the relative zone/spot position, R p g, showed good correlation with the results predicted by the computing calculation.

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In the paper, the influence of the addition of different ion-pair reagents — sodium-1-heptane sulfonate (HS), tetrabutylammonium chloride (TBA), and bis(2-ethylhexyl)hydrogen phosphate (HDEHP) — to the mobile phase on the velocity of the electroosmotic flow (EOF) of the mobile phase in pressurized planar electrochromatography (PPEC) was examined. During the experiments, glass-based high-performance thin-layer chromatography (HPTLC) RP-18W chromatographic plates were used as the stationary phase. The mobile phase was composed of acetonitrile and water in the ratio 25:75 (v/v) with acetic buffer (4 mM) and with or without ion-pair reagent. Our research shows that ion-pair reagent in the chromatographic system significantly affects the value of zeta potential and the value of the velocity of the electroosmotic flow of the mobile phase. The results of our study also demonstrate that, in PPEC, as in other chromatographic techniques, a small addition of ion-pair reagents affects the selectivity of the separation.

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Our article presents the comparison of two methods: high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC), implemented for the separation of a test mixture of purine derivatives. The two methods were compared in terms of separation selectivity and separation time. Our results show that PPEC enables the separation of the mixture (azathioprine, caffeine, theobromine, theophylline and acyclovir) which could not be efficiently separated in the HPTLC system, due to the different selectivities of separation. PPEC also enables to obtain a much faster separation, performed on the longer distance, in comparison to HPTLC. This makes PPEC a technique which can be useful in the analysis of purine derivatives and other drugs.

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