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  • Author or Editor: Paweł Płocharz x
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We have investigated the use of pressurized planar electrochromatography (PPEC) and planar chromatography (TLC) for reversed-phase separation of a mixture of acetylsalicylic acid, caffeine, and acetaminophen. The mixture was separated on C18 plates; the mobile phase was prepared from acetonitrile (ACN), buffer, and bidistilled water. The effects of operating conditions such as mobile phase composition, type of the stationary phase, and mobile phase buffer pH on migration distance, separation selectivity, and separation time in TLC and PPEC were compared. The results showed that pressurized planar electrochromatography of these drugs is characterized by faster separation, better performance, and different separation selectivity. In conclusion, PPEC is a very promising mode for future application in pharmaceutical analysis.

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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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The separation of 1-fluoro-2,4-dinitrophenyl-5-l-valine amide (FVDA) diastereomeric derivatives of aspartic acid, cysteine, and histidine by means of high-performance thin-layer chromatography (HPTLC) as well as pressurized planar electrochromatography (PPEC) techniques in systems with HPTLC RP-18W plates and the various acetonitrile—buffer mobile phases is presented. The influence of the mobile phase components, i.e., acetonitrile concentration and buffer kind on migration distance of the solute zones, was investigated. The effect of mono (formic) and various dicarboxylic acids (oxalic, malonic, maleic, malic, succinic, tartaric, and pimelic) as the mobile phase buffer components on the solute retention was studied. It is observed that an increase of acetonitrile content of the mobile phase affects the solute zone migration and retention in PPEC and HPTLC. What is more, the separation selectivity in the latter and former techniques differs. The PPEC mode presents a higher efficiency in comparison with HPTLC. The solute separation with electromigrational system is more fragile on the kind of acid used as mobile phase buffer component than with chromatographic method. Nevertheless, the influence of the kind of mobile phase buffer component on solute selectivity and retention in both techniques was determined. The electrokinetic (zeta) potential of the stationary—mobile phase interface was measured and compared with the solute retention data of both techniques.

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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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