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  • Author or Editor: Mihaela Vlassa x
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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.

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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.

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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.

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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.

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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).

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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.

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Mihaela Vlassa, Virginia Coman, Miuţa Filip, Florina Copaciu, Aurora Mocanu and Maria Tomoaia-Cotişel

The basic of all proteins is constituted by approximately 20 common amino acids that differ only in the structure of their side chain. The purpose of our work was to use the overpressured layer chromatography (OPLC) technique for the separation and identification of the essential and non-essential amino acids from some most common proteins, like hen egg yolk protein, bovine serum albumin (BSA), and Type I Collagen from bovine achilles tendon. In this order, the target proteins were acid-hydrolyzed and derivatized. For the separation of essential amino acids from egg yolk, two successive OPLC developments (normal and overrunning) were performed, followed by direct derivatization with 4-hydroxybenzaldehyde and ninhydrin on the chromatoplate for identification. In the hydrolyzed egg yolk, nine essential amino acids were identified. Between lysine and histidine, a poor separation was obtained. The amino acids from BSA and Type I Collagen were separated and identified as phenylthiohydantoin (PTH) derivatives by OPLC. The supposed identity of the amino acids as PTH derivatives was confirmed by reversed-phase high-performance liquid chromatography (RP-HPLC). Seven essential amino acids (arginine, histidine, threonine, valine, methionine, isoleucine, and leucine) were found in bovine serum albumin (BSA), and six (histidine, threonine, valine, methionine, leucine, and lysine) in Type I Collagen. The same eight non-essential amino acids (cysteine, asparagine, glutamine, glycine, alanine, serine, tyrosine, and proline) were identified in these two proteins. By RP-HPLC, other two non-essential amino acids (aspartic acid and glutamic acid) were found both BSA and Type I Collagen. Cysteic acid was also found in BSA. In our samples, tryptophan was missing due to its destruction during hydrolysis.

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Thin-layer chromatography (TLC) is a frequently used technique for the separation of polar and non-polar compounds, with a rich literature in this field. The aim of this paper is to show the TLC adsorbent quality of the Nevşehir volcanic tuff from Turkey that is compared with the Mirșid volcanic tuff from Romania. Our experimental investigations have shown that it is possible to achieve TLC plates coated with Nevşehir volcanic tuff, in natural occurrence, excepting grinding and sieving processes, which can be used for the separation of polar compounds, such as amino acids or food dyes. In the present article, modern techniques for characterizing the volcanic tuff powders, namely, X-ray diffraction, inductively coupled plasma–optical emission spectrometry, scanning electron microscopy, specific surface area and porosity measurements, and infrared spectroscopy, were used in addition to the chromatographic testing. TLC plates coated with Nevşehir tuff were prepared and tested at the separation of some amino acids, obtaining good results. Also, the impregnation of Nevşehir tuff with NaOH and NaCl, respectively, allowed the separation of some hydrophilic dyes. The obtained results have contributed to understand the chromatographic properties of the Nevşehir volcanic tuff. The TLC capability of the Nevşehir tuff can enlarge the pallete of inexpensive adsorbents with possible applications in the field of layer chromatographic separations.

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In our previous papers, we defined layer (planar) dielectrochromatography and we presented its fundamentals (theoretical aspects) such as the displacement of dielectric liquids under nonuniform external alternating electric fields (dielectroosmotic flow [DEOF] effect), the displacement of solute particles or polarized granules (dielectrophoresis [DEP] effect) in electric fields generated by armatures, the theoretical evaluation of the electric intensity generated in the stratified dielectrics, etc. Ready-to-use plates of alumina, silica gel, and cellulose were used for experiments. The obtained results have encouraged us to create our own TLC plates based on alumina enriched with compounds of high dielectric constants like barium sulfate, barium titanate, and titanium dioxide. In this paper, we present the preparation of seven plates containing increasing amounts (1, 2, 3, 4, 6, 8, 10) g of barium titanate in 35 g alumina, the methodology used in their characterization, as well as the obtained results and the perspectives of using this ingredient.

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