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  • Author or Editor: Irena Malinowska 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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Raw materials quality assessment is a very important factor, enabling products creation up to the international standards. In this investigation, the qualitative composition of bioactive plant extracts has been checked. The tested extracts have been obtained by the use of supercritical carbon dioxide extraction and can be utilized as raw materials in a commercial production of a wide range of many different goods. Plant extracts of raspberry (Rubus idaeus), strawberry (Fragaria ananassa), blackcurrant (Ribes nigrum), aronia (Aronia Medik.), Japanese rose (Rosa rugosa Thunb.) seeds, and palmetto palm (Sabal minor) fruit have been examined. In these extracts, saturated, monounsaturated, and polyunsaturated fatty acids as well as polyphenols have been identified using thin-layer chromatography (TLC) with aqueous-organic mobile phases. Appropriate content of these components tends to be a determinant of human organism operation. In our investigation, the plant extract components, especially saturated and unsaturated fatty acids and polyphenols, have been tested using micellar chromatography. Different micellar environments, containing polioxyethylene (23) lauryl ether (Brij35), sodium dodecyl sulfate (SDS), and cetyltrimethylammonium bromide (CTAB) as a main component of micellar mobile phases, have been utilized. The analyte-micelle association constants (K ma) from Foley’s equation have been compared for each of these environments.

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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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The effect of electric fields on mobile phase migration velocity and on the retention of chromatographed solutes has been investigated for so-called horizontal electric fields with sample applied at the anode and cathode ends of the plates. An electric field can also affect the surfaces of stationary phases. These investigations were performed in a so-called vertical electric field at a gradient voltage 12 kV cm −1 . The effect of the electric field on the apolar component of the surface free energy was determined for six popular stationary phases; for silica and aluminum oxide it was possible to determine the acidic and basic components of the surface free energy. The effect of electric fields on the zeta potential of silica-methanol and aluminum oxide-water systems was also demonstrated.

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Conditions have been established for TLC analysis and determination of the flavonol truxinic esters daglesiosides I and II in species of the family Pinaceae . Optimization of the separation of eleven flavonoids, including daglesiosides I, II, III, and IV, trans -tiliroside, trans -ditiliroside, kaempferol, quercetin, isorhamnetin, hyperoside, and astragalin, which are present in the methanol extract of Pseudotsuga menziesii , was performed on two types of layer — glass plates coated with RP-18F 254S and diol F 254S . Good resolution was achieved on diol F 254S layers by use of multiple gradient development with a mixture of chloroform and ethyl acetate. Under these conditions the presence of daglesioside I was demonstrated in two other species of Pinaceae — Cedrus atlantica and Cedrus atlantica var. glauca — and the flavonoid complex occurring in Pseudotsuga menziesii was completely separated by use of 2D TLC on coupled silica gel and RP-18 layers.

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This paper describes the effect of the method of application of samples to chromatographic plates on the R F values and resolution of the separated compounds and number of theoretical plates in the chromatographic system. R F values, resolution, and number of theoretical plates of the chromatographic system have been compared for different modes of solute application — by means of an applicator, as a spot and a band, by means of a micropipette, and in a system in which filter paper was used as a concentrating zone.

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Extracts of tertiary and quaternary alkaloids from Chelidonium majus L. have been separated by OPLC. Samples of different volumes were developed on SiO 2 layers in a BS-50 Personal OPLC chamber using different mobile-phase velocities from 100 to 400 µL min −1 . The effect of mobile-phase velocity in OPLC on properties such as retardation factors, reproducibility, efficiency, number of theoretical plate, HETP , and resolution, was investigated.

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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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