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  • Author or Editor: Marek Studziński x
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As it was presented in our previous works, applying external magnetic field during chromatogram development results in changes of retention of chromatographed solutes which can be used for adjustment of their chromatographic behavior, in order to optimize the separation. In this paper, we would like to present the influence of application of external magnetic field during chromatogram development on thin-layer chromatography (TLC) and high-performance thin-layer chromatography (HPTLC) plates on separation of ingredients of plant extracts, which are multicomponent mixtures and are very difficult to separate under conventional chromatographic conditions.

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The effect of a magnetic field on the planar chromatographic retention of some PAH has been investigated. The horizontal chamber was placed between two neodymium magnets and chromatograms were developed in the magnetic field created. The effect of the magnetic field was tested for single-component and binary mobile phases containing n -alkanes and aromatic hydrocarbons. PAH were used as solutes. The results obtained showed that magnetic fields can affect the retention and shape of the chromatographic bands of the solutes investigated. The effect depends on the type of mobile phase, the properties of the adsorbent layer and the mode of development of the chromatogram (development distance).

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As it was shown in earlier experiments, magnetic field can influence various processes taking part in nature. One of them might be the permeation of chemical compounds across biological membranes. An excellent tool for investigations on that subject is chromatography. Basing on retention measurements performed using reversed-phase thin-layer chromatography (RP-TLC) and micellar liquid chromatography—thin-layer chromatography (MLC—TLC), descriptors of lipophilicity were calculated for the group of 1,2,4-triazole derivatives. The experiments were performed in moderate (≈0.4 T) magnetic field and simultaneously outside it. The analysis of the obtained data showed that the presence of an external static magnetic field can alternate the obtained descriptor values which allows to assume that the ability of passive permeation of the investigated substances across cellular membrane also changes. The intensity of changes depends on the structure of the chromatographed substance and the lipophilicity measurement method.

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Magnetic field can influence some processes taking part in the solid—liquid interphase area. An excellent tool for the investigation of this phenomenon is thin-layer chromatography. In this experiment, the influence of magnetic field parallel with chromatogram development direction on retention and system efficiency was investigated. The application of superconducting magnet allowed for generating the adjustable magnetic field up to about 2 T and allowed for investigation on dependence between inductivity of the field and retention changes of the chosen polyaromatic hydrocarbons. The obtained results show that the presence of magnetic field alternates the interactions among all components of a chromatographic system. Thus, in order to predict substance retention and system efficiency changes induced by the presence of the field, more parameters than the force acting on chromatographed molecule must be taken into account.

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In this study, an investigation on the effect of the magnetic field on interphase phenomena influencing chromatographic separation was performed using thin-layer chromatography method. The presence of perpendicular to plane of the plate and the direction of chromatogram development magnetic field influences the interaction among all components of the chromatographic system. In consequence, the retention and efficiency of the investigated compounds in the given system should be altered. In this article, the effect of the field presence regarding retention mechanism, distance of development, and particle size of stationary phase for chosen derivatives of 2-(2,4-dihydroxyphenyl))-1,3,4-thiadiazoles is being investigated. The alteration of each abovementioned parameter affects the retention change caused by the field. It was also observed that the retention changes depend also on the structure of the studied compound, which may be a useful information for investigations on properties of newly synthesized compounds.

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In the presented paper, the influence of the static electric field on retention, and in consequence separation, of tropane alkaloids present in Datura innoxia Mill. extract was demonstrated. Thin-layer electrochromatography (ETLC) on initially dry layers was used as the investigation method. The results obtained by ETLC were compared with the data obtained in thin-layer chromatography (TLC) analogous systems. Pseudo-reversed-phase systems (stationary phase — silica gel, mobile phase buffer at different pH and methanol mixture with different content of the methanol) were used. The presence of the electric field influences the retention parameters of the investigated compounds. The influence depends on the pH of the buffered mobile phase, composition of the mobile phase, and turn of the electric field lines in relation to the mobile phase migration direction. In the mobile phase, in which some of the alkaloids are in the ionic form, the significant differences between retention in cathode side and anode side were observed due to electrophoretic migration of the solutes, so direction of the electric field lines can be one of the systems’ optimization factor. The experiment proves that full separation of the investigated mixture ingredients is possible in ETLC only.

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