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Two-dimensional (2D) separation of eight amino acids has been achieved by HPTLC in the first dimension and pressurized planar electrochromatography (PPEC) in the second, orthogonal, dimension. Separation selectivity in PPEC was very different from that in HPTLC. This attribute of these systems enabled complete separation of the amino acids. Chromatography was performed on reversed-phase plates with acetonitrile-buffer mobile phase. PPEC was performed after complete prewetting the plate, including the sample zones.

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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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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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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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Thin-layer chromatography (TLC) and pressurized planar electrochromatography (PPEC) of amino acids in normal-phase system is presented. The results have been obtained for various normal-phase high-performance thin-layer chromatography (HPTLC) and PPEC systems with the mobile phase that comprised acetonitrile in the concentration ranges 40–90% and 20–90%, respectively, and HPTLC silica gel 60 F254s plates from Merck. The data obtained show differences in separation selectivity between HPTLC and PPEC systems. The respective separation selectivities have been obtained for HPTLC and PPEC systems with the mobile phase buffer pH in the range 2.6–9.0. The retention of amino acids in HPTLC systems has demonstrated minor dependence on buffer pH, while, in analogous PPEC systems, migration distances of the solutes have shown considerable changes. The differences of separation selectivity in HPTLC and PPEC systems are interpreted in terms of solute partition in the former and solute partition and electrophoresis in the latter.

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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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This report describes the first results from coupling of pressurized planar electrochromatography (PPEC) and desorption electrospray ionization (DESI) mass spectrometry (MS). Nine analytes were separated in 2.0 min by PPEC and detected by direct analysis of the TLC plate using DESI coupled to a tandem mass spectrometer. The total analysis time was less than 10 min and sample preparation was minimal. Combination of DESI-MS with PPEC enhances the specificity and sensitivity of detection of analytes in a mixture.

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Separation of 2,4-dinitrophenyl-5-l-valine amide derivatives of some amino acids (leucine, isoleucine, valine, asparagine, cysteine, tryptophane) L and D-enantiomers with high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) is presented. The separation mechanism in the PPEC technique involves two effects (partition and electrophoresis) whereas HPTLC system employs only one (partition). The separation process in both modes was carried out with the HPTLC RP-18 plates. Influence of the aqueous-organic mobile phase composition (acetonitrile concentration, buffer type, its pH) on migration distance of the solute zones is investigated and compared for both techniques. The PPEC system turns out to be more sensitive to buffer type and pH than HPTLC one. Additionally, the electrophoretic effect is responsible for different separation selectivity in PPEC system in comparison to that in HPTLC one. The retention of DL-diastereoisomer derivatives of amino acids is stronger in comparison with its LL-antipodes for both separation techniques. The statistic evaluation of the migration distance in PPEC and TLC systems shows similar RSD.

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