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- Author or Editor: Virginia Coman x
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To simulate front displacement through porous media (TLC plates) the effect of the axisymmetric alternating electric fields on liquids confined in capillary tubes was studied. This electric field causes liquid displacement through capillary tubes with great velocity, the main action being on the liquid column meniscus. Capillary tubes were used to enable understanding of the flow phenomena which occur in porous media. It was observed that the displacement velocity of the liquids confined in capillary tubes depended on the magnitude of the alternating electric field, the electric properties (conductivity, permittivity) of the liquids, the frequency of the current, and the tube material.In normal TLC practice, migration of the mobile phase through the layer is controlled by capillary forces. The velocity and migration distance of the mobile-phase front in prous media can be increased by application of an external electric field, an effect called by us ‘dielectroosmotic flow’ (DEOF), because of its similarity with electrokinetic phenomena. DEOF is observed on different TLC plates and paper strips developed with non-polar and polar solvents. As a result the separation of some compounds was improved. This method is a hybrid of electric forced flow and classical TLC; we have named it ‘planar dielectrochromatography’ (PDEC).A horizontal chromatographic chamber has been constructed and has been used to investigate the principles of planar dielectrochromatography, specifically the increase in front velocity and the dielectrophoretic force generated at granule level on different ready-to-use plates.
Drawn by capillary forces the developing solvent (mobile phase) migrates through the thin layer (stationary phase) over a defined distance. During this process the sample is separated into fractions. In TLC the flow velocity of solvent is inversely related to the distance migrated by the solvent front. For this reason classical TLC is time-consuming and usually of low chromatographic efficiency. To improve the separation selectivity suitable transverse alternating electric fields have been used to modify the mobile phase front velocity and the migration distance of solutes. In this paper, a vertical chromatographic chamber has been constructed and has been used to study experimentally the principles of planar dielectrochromatography, particularly the increase of the mobile phase front velocity and of the dielectrophoretic force generated at granule level on alumina plates. The equicurrent and countercurrent arrangements of armatures were taken into consideration. Good results were obtained in the countercurrent arrangement, the resolution of solute separation being improved.
Arapid and simple method for simultaneous quantitative analysis of the natural carbohydrates fructose, glucose, and sucrose in different types of wine (white and red; dry, semi-dry, semi-sweet, and sweet) by OPLC in overrunning mode is presented. The compounds were separated on precoated silica gel F254 OPLC plates with acetonitrile-water 26:4 (v/v) as mobile phase. Visualization was by spraying with a mixed solution of aniline and diphenylamine, then densitometry in absorbance mode was performed at 420 nm. Linear regression analysis of the calibration data was indicative of a good linear relationship between the peak area and the concentration in the range 0.5–5.0 μg per band (r glucose 0.99051, r fructose 0.98547, r sucrose 0.99506). In this paper we give the results obtained from analysis of 49 samples of white and red wines. In the most of the samples we did not find sucrose, only fructose and glucose in different ratios depending on the type of the wine. We found few white and red wine samples for which the content of reducing sugars was not in agreement with the label description. The results obtained for the wines show this OPLC method can be useful for routine monitoring of the quality of commercial wine. Amajor advantage of the method is that it enables simultaneous analysis of approximately 20 samples in less than 2 h.
Our previous work on planar dielectrochromatography (PDEC) showed that application of transverse electric fields to porous media can affect the separation. In experiments with a vertical PDEC (V-PDEC) chamber we observed that when a potential is applied some of the metal components used to construct the chamber generate electrical fields that can cause deviation of the spots from the vertical, disturbing the separation process. Starting from this statement we changed the geometry of the electric field used in the V-PDEC chamber to obtain the most favorable chromatographic results. For this we conceived and experimented with five types of armature (periodic lamellar strips, lamellar strips of variable widths, and spherical, conical, and Félici shape). The shapes of the armatures generate electric fields with different geometry that have characteristic effects on the chromatographic process. The experiments were performed on alumina plates with toluene as mobile phase and a lipophilic dye mixture as solutes. The tests showed that different electric field geometries which do not completely cross the glass support of the TLC plates can be used. This results in enhancement of the intensity of the electric field in the chromatographic layer, especially for the spherical and conical armatures. With these two armatures we achieved the best resolution of the solutes.
Drawn by capillary forces the developing solvent (mobile phase) migrates through the thin layer (stationary phase) over a defined distance. During this process the sample is separated into fractions. To improve separation selectivity suitable transversal electric fields have been used to modify the mobile phase front velocity and the migration distance. In this paper, a horizontal chromatographic chamber has been constructed and has been used to study experimentally the principles of planar dielectrochromatography, in particular the increase of the mobile phase front velocity and the dielectrophoretic force generated at granule level on different ready-to-use Macherey-Nagel plates.
The objective of this paper is to report a procedure for the extraction and the determination of five textile dyes (Lanasyn Blue F-L 150, Lanasyn Dark Brown M-GLN, Lanasyn Red M-GA, Nylosan Dark Brown S-MBL, and Nylosan Red N-2RBL) which were not yet studied in literature by high-performance thin-layer chromatography. For SPE of these dyes, four types of Strata cartridges (WAX/NH2, SAX, C18-U and C18-E) were tested. The best results were obtained on Strata WAX/NH2. The dyes were separated on precoated Alugram RP-18W/UV254 plates with the n-butanol-ethyl acetate-5% ammonium hydroxide 4:4:1 (v/v) mobile phase. The densitometric scanning was performed at 550 nm. Linear regression analysis of the calibration data indicated a good linear relationship between the peak area and the dye concentration in the range of 20–60 ng per band. For the HPTLC method, the detection and the quantification limits of the studied dyes were calculated. The obtained detection limits (ng per band) were: 6.6 for Lanasyn Blue F-L 150, 5.90 for Lanasyn Dark Brown M-GLN, 3.38 for Lanasyn Red M-GA, 5.49 for Nylosan Dark Brown S-MBL, and 1.07 for Nylosan Red N-2RBL. The SPE-HPTLC procedure was applied to monitor these textile dyes in the effluent wastewater samples collected from a textile factory from Romania.
Excessive use of antibiotics leads to their occurrence into the environment. In spite of their benefit properties and desired effects during the therapeutic applications, the same properties can be disadvantageous for the environment having negative influences over the plants and microorganisms and the potential risks for human health. Regarding the monitoring of antibiotics and their subsequent elimination from environment, it is necessary to develop analytical procedures for their determination. In the present study, the quantitative determination of seven antibiotics belonging to three different classes is reported: tetracyclines (tetracycline and doxycycline), cephalosporins (ceftazidime and ceftriaxone), and penicillins (amoxicillin, ampicillin, and penicillin G) from surface waters. The proposed procedure consists of the solid phase extraction (SPE) of studied antibiotics from river water samples, their separation by high-perfomance thin-layer chromatography (HPTLC), and quantification by UV densitometry. The antibiotics were extracted from water matrices using hydrophilic-lipophilic-balanced Oasis HLB cartridges. The cartridge efficiency of the SPE method was checked by recovery experiments and evaluated by HPTLC. The chromatographic separation was performed on pre-coated Alugram SIL G/UV254 plates with ethyl acetate-methanol-acetone-water 5:2.5: 2.5:1.5 (v/v) mobile phase. The bands were detected and quantified at 254 nm by densitometry. For method validation, studies of selectivity, linearity, limits of detection and quantification, and precision and accuracy were achieved. The proposed procedure was applied to the determination of studied antibiotics on surface water samples collected from Someoul Mic River (Romania).
The profiles of anthocyanins and anthocyanidins present in berry fruits can be used as fingerprints for the evaluation of authenticity of raw materials, juices, fruit extracts, and food products. The aim of our work was to establish the authenticity of fruit juices from the market according to the label inscription. With this end in view, we used spectroscopic and TLC techniques for the preliminary identification of main groups of anthocyanins and to obtain a fingerprint of each berry fruit used in the preparation of juice. For the same purpose, we achieved a RP-HPLC method for the determination in detail of the composition of natural pigments, such as anthocyanins from alcoholic extracts of colored fruits and anthocyanidins from their hydrolyzed products. The RP-HPLC chromatographic fingerprints gave us the possibility to identify seventeen anthocyanins (glycosylated anthocyanidins) and five major anthocyanidins (delphinidin, cyanidin, petunidin, pelargonidin, and malvidin) from the extracts of colored fruits.The TLC separation was achieved on cellulose pre-coated plates developed with concentrated hydrochloric acid-glacial acetic acid-water as mobile phase followed by densitometric measurements in visible. The HPLC separation was carried out on ODS-2 Hypersil column by gradient elution and detection at 520 nm. The mobile phase was a mixture of acetonitrile and phosphoric acid buffer in different ratios.Our methods have been successfully applied to find the fingerprint of anthocyanins and anthocyanidins of eight berry fruits which we used as reference materials at the analysis of fruit juices from market in order to establish their authenticity and conformity with the label inscription.
Some of the physical properties of dielectric liquids are influenced by electric fields. Interesting results were obtained in this work by applying external alternating electric fields to chromatographic media (paper or TLC plates) filled with dielectric liquids. Capillary tubes were used to enable understanding of the flow phenomena which occur in porous media. It was observed that the displacement velocity of the liquids confined in the capillary tubes depended on the magnitude of the alternating electric field, the electric properties (conductivity, permittivity) of the liquids, the frequency of the current, the tube diameters, the shapes of the molecules, and the tube material. Evident electrokinetic effects (dielectroosmotic flow) were observed on silica gel layers and paper strips developed with non-polar and polar solvents. As a result the separation resolution of non-ionic compounds was improved. This method is a hybrid of electric forced flow and classical diffusion; we have named it planar dielectrochromatography.
Chemically modified acidic alumina T stationary phases have been prepared by organosilylation with the trifunctional organosilicon compounds n -octadecyltrichlorosilane, 3-mercaptopropyltri-methoxysilane, and N -(2-aminoethyl)-3-aminopropyltrimethoxysilane. These chemically modified phases were characterized by elemental analysis, measurement of specific surface area, FTIR spectroscopy, 13 C CP/MAS NMR spectroscopy, mass spectrometry, and thermal analysis. The TLC behavior of unmodified and chemically modified acidic alumina T has been tested by separation and identification of some dyes and benzo[ a ]pyrene derivatives.
