Fast separation and quantification of C60 and C70 fullerenes using thermostated micro thin-layer chromatography.

Thermostated micro planar chromatography was applied for systematic separation studies of C60 and C70 fullerenes using n-alkanes as mobile phases on TLC and HPTLC plates coated with polyamide, silica gel, aluminum oxide as well as two types of octadecylsilica (C18) sorbents. Retention data were collected at constant temperature at 20 degrees C (+/-0.05 degrees C) using an unsaturated chamber mode with an eluent, such as n-pentane, n-hexane and n-heptane. The separation results under both saturated and unsaturated chamber modes for selected mobile/stationary phases were also examined, and several parameters, including separation factor (alpha) and resolution (R(S)), were compared with data obtained with high-performance liquid chromatography conditions. Interestingly, C60/C70 fullerenes separation performed on HPTLC plates with a developing distance of 45 mm was better for those observed on a 25 cm length analytical HPLC column under similar conditions to that on carbon coverage of the stationary phase, n-hexane as the mobile phase and separation temperature (R(S) = 1.84 and 1.68 for HPTLC, and HPLC, respectively). Moreover the advantage of the planar chromatographic separation of fullerenes studied is a short elution time of less than 6 min. Furthermore, the reported separation protocol shows a capability for the evaluation of fullerenes quantity in commercial samples.     

Retention and separation studies of cholesterol and bile acids using thermostated thin-layer chromatography.

The influence of temperature on retention and separation of cholesterol and bile acids, using reversed-phase thin-layer chromatography, was studied. As mobile phases methanol-water mixtures of various compositions were used. Chromatographic experiments were performed using vapor-saturated chambers at temperatures ranging from 5 to 60 degrees C. A linear relationship between R(M) values and temperature (1/T) as well as mobile phase composition was observed. The elution order of steroids under the conditions investigated was discussed. Each chromatogram was evaluated using simple optimization parameters and the best chromatographic conditions for the separation of multicomponent samples were chosen.     

Azeotropic mixtures as mobile phase for thin-layer chromatography of organic fluorescent dyes

Reproducible R _f values in the thin-layer chromatography (TLC) of various fluorescent dyes (amino derivatives of naphthoylenebenzimidazole, naphthalimide, benzanthrone, phenalenone, including phosphorus-containing luminophores) were shown to be obtained by elution with binary homogeneous azeotropic mixtures of solvents of different polarity. Some trends in the chromatographic mobility were established governed by the structural features of the groups of compounds under study.     

Removal of organic dyes from water by liquid-liquid extraction using reverse micelles

In the present work, solvent extraction using reverse micelles is proposed for the removal of organic dyes from water. In this approach, the dye is solubilized in the aqueous core of the reverse micelles, which are present in the organic phase. The organic phase is subsequently separated from the aqueous phase leading to signifi-cant removal of dye. Experimental results reveal that the electrostatic interaction between the oppositely charged surfactant head group present in the reverse micelles and the dye molecule plays a key role in the separation. The removal of the anionic methyl orange dye from water is carried out in the presence of cationic hexadecyltrimethyl ammonium bromide surfactant, whereas the removal of the cationic methylene blue dye is carried out in the presence of anionic sodium dodecylbenzene sulfonate surfactant. Amyl alcohol is used as the solvent. The influence of parameters such as dye concentrations, surfactant concentrations, pH, and KCl and NaBr concentrations on the percentage removal of dye was studied. The percentage removal of dye is decreased with the increase in dye concentration in the feed. The increase in surfactant concentration resulted in higher dye removal, because more reverse micelles could be hosted in the organic phase. The increase in aqueous phase pH resulted in enhanced removal of methyl orange from water, while in the case of methylene blue the percentage removal decreased. The increase in KCl and NaBr concentrations resulted in decreased percentage removal of methylene blue, whereas the percentage removal of methyl orange was increased. The effect of pH and salt concentration is explained based on charge transfer mechanism and electrostatic interactions and dye-surfactant complex formation.     

Environmental analysis of organic compounds in water using solid phase micro extraction

Solid Phase Micro Extraction (SPME) involves exposing a fused silica fiber coated with stationary phase to a contaminated water sample. The organic analytes become partitioned between the stationary phase and the water and when equilibrium is reached the fiber is removed from the solution and the analytes are thermally desorbed in the injector of a gas chromatograph. The fiber is contained in a syringe to facilitate handling. Factors which affect linear range, limit of detection, and total analysis time are discussed with regard to the development of a method for analysis of volatile compounds in environmental water samples. The sensitivity of the method was determined by the thickness of the film of stationary phase; the equilibration time, however, increased with the film thickness, although it can be minimized by use of a cross-shaped stirrer bar. Increasing the thickness of stationary phase in the analytical column enables the cryofocusing temperature to be increased from ?40 to ?15°C. With an ion trap mass spectrometer, detection limits required by the US Environmental Protection Agency are met for all compounds except chloromethane and chloroethane. The method has been applied to environmental water samples.     

Determination of aminophenol isomers in water samples by extraction and thin-layer chromatography densitometry

A TLC densitometric method for the determination of the aminophenol isomers in water samples has been developed. The aminophenols are first extracted into chloroform-isoamylalcohol (1:2) mixture. The extracted aminophenols are separated on a TLC plate and visualized by spaying solution of 2,4,7-trintro-9-fluorenone in acetone. The colored spots are scanned for light absorption or reflection and the amount of each aminophenol is evaluated.     

Quantitative determination of some food dyes using digital processing of images obtained by thin-layer chromatography

A high-performance thin-layer chromatographic method combined with image processing of scanned chromatograms was developed for the determination of some food dyes (tartrazine, azorubine and Sunset Yellow) in different products. Porous silica gel with 3-aminopropyl functional groups attached to the matrix was used as stationary phase and a mixture of isopropanol, diethyl ether and ammonia (2:2:1, v/v/v) formed the mobile phase. Quantitative evaluation was performed using special-purpose software. The linearity of the analytical procedure was sustained by the numerical parameters such as correlation coefficient (0.9952-0.9980) and standard error of determination (0.03-0.20). The limits of detection were found to be within the range of 5.21-9.34 ng/spot, and the limits of quantification between 10.21 and 18.09 ng/spot. Recovery studies performed on two levels of concentration gave values between 96.39 and 102.76%. These results show that the regression approach provides rigorous and realistic detection and quantification limits and as a consequence can be routinely applied to other analytical systems. This method does not require expensive analytical instruments compared with classical densitometry and provides a reliable quantitative evaluation with minimum of time.     

A simple technique for the preparation of micro slides for thin-layer chromatography

Summary A simple, inexpensive apparatus and procedure are described for the rapid preparation of coated micro slides for thin-layer chromatography. Although micro slides of varying sizes may be coated in this apparatus, the commercially-available Breed Brew slide is especially advantageous since it permits more analyses to be run on each chromatoplate and offers a longer developmental pathlength. A convenient, readily-constructed marking template which can accommodate micro slides of varying sizes is also presented.

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Zusammenfassung Ein einfacher, nicht aufwendiger Apparat und ein Verfahren für die rasche Beschichtung von Objektträgern für die Dünnschichtchromatographie wurden beschrieben. Zwar können Objektträger verschiedener Größe beschichtet werden, die handelsüblichen Breed-Brew-Platten, wie sie zur Bakterienzählung verwendet werden (51×115 mm), sind jedoch besonders vorteilhaft, da mehrere Analysen mit längerer Laufstrecke auf jeder Platte gleichzeitig ausführbar sind. Eine Schablone zur Markierung von Objektträgern verschiedener Größe wurde ebenfalls beschrieben.

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Résumé On décrit un appareillage simple et peu coûteux, avec un mode opératoire pour préparer rapidement des revêtements micro pour chromatographie en couche mince. Bien que l'on puisse recouvrir des lamelles micro de diverses tailles à l'aide de cet appareil, la lame «Breed Brew» disponible dans le commerce se montre particulièrement avantageuse puisqu'elle permet d'effectuer davantage d'analyses sur chaque chromatoplaque et qu'elle offre un trajet plus long pour le développement. On présente également un modèle pratique et rapidement construit pour la graduation; il peut s'adapter aux microplaques de diverses tailles.

     

Separation and micro determination of lipids by thin-layer chromatography followed by densitometry

Summary A method is presented for the rapid analysis of mixtures of lipids, particularly those from blood serum. The lipids are separated by thin-layer chromatography on silicagel, then charred with 10% aqueous sulphuric acid and the amount of carbon on the slides is measured densitometrically. 5–10 g of lipid mixture are needed for determination of the relative amounts of free sterol, sterol esters, glycerol esters, free fatty acids and total phospholipids.

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Zusammenfassung Es wird eine Methode beschrieben zur schnellen Analyse von Lipidgemischen, insbesonders von Lipiden aus Blutserum. 5–10 g eines Gemisches werden mit Hilfe der Dünnschicht-Chromatographie auf Kieselgel in Sterinester, Glycerinester, freie Steroide, unveresterte Fettsäuren und Phospholipide getrennt. Nach Verkohlung durch Erhitzen mit 10%iger Schwefelsäure werden die verschiedenen Typen densitometrisch bestimmt.

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The investigation forms part of a study on the chemical aspects of atherosclerosis, carried out under the auspices of the Netherlands Organisation of Health Research TNO.     

Quantitation of polyamines using thin-layer chromatography and image analysis

Efficient separation of dansylated polyamines can be achieved by thin-layer chromatography (TLC). Quantitation, however, can be laborious because it requires removal of the silica gel and the fluorescing derivative from the glass plates, elution in a suitable solvent, and estimation with a fluorescence spectrophotometer. We report here a relatively simple and rapid method for the quantitation of dansylated polyamines that employs an image analyzer without removal from the glass TLC plates.     

Analysis of organic pollutants in water at trace levels using fully automated solid-phase extraction coupled to high-performance liquid chromatography

Summary A method has been developed for the determination of trace levels of 32 pesticides, 19 explosives and 16 polycyclic aromatic hydrocarbons (PAH) in water in three individual steps. Solid-phase enrichment (SPE) is coupled to high-performance liquid chromatography (HPLC) with a fully automated system. The organic pollutants are enriched on reusable cartridges packed with adsorbent materials: pesticides and explosives on a mixed bed of divinylbenzene-ethylvinylbenzene copolymers (LiChrolut EN^?) and perfluorinated polyethylene (PolyF^?), and polycyclic aromatic hydrocarbons on C₁₈-modified silica (Zorbax^? ODS1). Thermally assisted desorption (TAD) has been shown to increase the recovery of analytes significantly. As all enriched analytes are transferred to the detector, only fifty millilitres of sample is needed for each single on-line analysis, compared with at least a litre for conventional methods. The separation of the enriched organic analytes is performed on specialized HPLC columns based on reversed-phase materials. The limits of detection of the system employed were found to be below 100 ng L⁻¹. Use of fluorescence detection for the polycyclic aromatic hydrocarbons resulted in limits of detection in the upper pg L⁻¹ range. Thek values, number of theoretical plates, the recovery rates and the limits of detection of this method for fast screening of organic pollutants from three fifty-millilitre aqueous samples are described. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Partition coefficients of organic compounds in new imidazolium based ionic liquids using inverse gas chromatography

Partition coefficients of organic compounds in four ionic liquids: 1-ethanol-3-methylimidazolium tetrafluoroborate, 1-ethanol-3-methylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium diethylphosphate were measured using inverse gas chromatography from 303.3 to 332.55 K. The influence of gas–liquid and gas–solid interfacial adsorption of different solutes on ionic liquids was also studied. Most of the polar solutes were retained largely by partition while light hydrocarbons were retained predominantly by interfacial adsorption on the ionic liquids studied in this work. The solvation characteristics of the ionic liquids were evaluated using the Abraham solvation parameter model.     

Low-parachor solvents extraction and thermostated micro-thin-layer chromatography separation for fast screening and classification of spirulina from pharmaceutical formulations and food samples

The goal of this paper is to demonstrate the separation and detection capability of eco-friendly micro-TLC technique for the classification of spirulina and selected herbs from pharmaceutical and food products. Target compounds were extracted using relatively low-parachor liquids. A number of the spirulina samples which originated from pharmaceutical formulations and food products, were isolated using a simple one step extraction with small volume of methanol, acetone or tetrahydrofuran. Herb samples rich in chlorophyll dyes were analyzed as reference materials. Quantitative data derived from micro-plates under visible light conditions and after iodine staining were explored using chemometrics tools including cluster analysis and principal components analysis. Using this method we could easily distinguish genuine spirulina and non-spirulina samples as well as fresh from expired commercial products and furthermore, we could identify some biodegradation peaks appearing on micro-TLC profiles. This methodology can be applied as a fast screening or fingerprinting tool for the classification of genuine spirulina and herb samples and in particular may be used commercially for the rapid quality control screening of products. Furthermore, this approach allows low-cost fractionation of target substances including cyanobacteria pigments in raw biological or environmental samples for preliminary chemotaxonomic investigations. Due to the low consumption of the mobile phase (usually less than 1 mL per run), this method can be considered as environmentally friendly analytical tool, which may be an alternative for fingerprinting protocols based on HPLC machines and simple separation systems involving planar micro-fluidic or micro-chip devices.     

Evaluation of the extraction efficiency of thermally labile bioactive compounds in Gastrodia elata Blume by pressurized hot water extraction and microwave-assisted extraction

Our earlier work showed that the stability of the bioactive compounds gastrodin (GA) and vanillyl alcohol (VA) in Gastrodia elata Blume behaved differently with varying compositions of water-ethanol using pressurized liquid extraction (PLE) at room temperature. To have a better understanding of the extraction process of these thermally labile compounds under elevated temperature conditions, pressurized hot water extraction (PHWE) and microwave-assisted extraction (MAE) methods were proposed. PHWE and MAE showed that GA and VA could be extracted using pure water under optimized conditions of temperature and extraction time. The extraction efficiency of GA and VA by the proposed methods was found to be higher or comparable to heating under reflux using water. The marker compounds present in the plant extracts were determined by RP-HPLC. The optimized conditions were found to be different for the two proposed methods on extraction of GA and VA. The method precision (RSD, n=6) was found to vary from 0.92% to 3.36% for the two proposed methods on different days. Hence, PHWE and MAE methods were shown to be feasible alternatives for the extraction of thermally labile marker compounds present in medicinal plants.     

Fabrication of highly crystalline covalent organic framework for solid-phase extraction of three dyes from food and water samples

Herein, a covalent organic framework, which was fabricated at room temperature by using 1,3,5-tris(p-formylphenyl) benzene and 1,3,5-tris(4-aminophenyl)benzene as building blocks, was employed as an adsorbent for solid-phase extraction of dyes including congo red, methyl blue and direct red 80 for the first time. The prepared covalent organic framework was properly characterized by different techniques and the results revealed that it had a uniform spherical structure, high crystallinity, satisfactory surface area, and good thermal stability. Moreover, the adsorption performance of the material was explored by using static and dynamic adsorption experiments and the results indicated that the material showed good adsorption capacities for three dyes with adsorption capacities in the range of 55.25–284.10 mg/g and the adsorption equilibrium can be achieved in 15 min. Further, to achieve the best adsorption effects of the material, the influence parameters such as pH, ionic strength, type of desorption solvent, and the material dosage in the solid-phase extraction column, were optimized in turn. Finally, under optimal conditions, the solid-phase extraction coupled with HPLC was applied to the analysis of dyes in food and water samples. The recoveries of dyes in actual samples were satisfactory, revealing the unique applicability of the material in the sample pretreatment field.     

AM1, PM3, and PM5 calculations of the absorption maxima of basic organic dyes

The absorption maxima, λ_max, of various organic dyes such as indigo, azobenzene, phenylamine, hydrazone, anthraquinone, naphthoquinone, and malachite green were calculated using the AM1, PM3, and PM5 semiempirical molecular orbital theories with the configuration interaction singles (CIS) and random phase approximation (RPA) approaches. The calculated λ_max were then compared with the values obtained by CNDO/S, INDO/S, ab initio CIS, and time-dependent density functional theory (TD-DFT). We found that the λ_max values calculated by AM1, PM3, and PM5 were in good correlation with the observed λ_max values. When B3LYP/cc-pVDZ optimized geometries were used, the square of the correlation coefficients between the calculated and observed λ_max, , at the AM1-RPA, PM3-RPA, and PM5-RPA levels were 0.891, 0.897, and 0.927, respectively. In particular, at PM5-RPA//B3LYP/cc-pVDZ was the largest among those obtained from all the other calculations including TD/B3LYP/cc-pVDZ//B3LYP/cc-pVDZ . Accordingly, the standard deviation of the difference between observed and calculated λ_max by the linear regression function at PM5-RPA//B3LYP/cc-pVDZ was the smallest. It was therefore concluded that this method was the most promising for the prediction of λ_max of various dyes among the computational methods studied here. When AM1 optimized geometries were used, at the AM1-RPA, PM3-RPA, and PM5-RPA levels were 0.822, 0.841, and 0.901, respectively, and they were also comparable to that at TD/B3LYP/cc-pVDZ//B3LYP/cc-pVDZ. Therefore, although some calibration efforts may be needed for AM1 geometries, PM5-RPA(CIS)//AM1 may be a second candidate available for the prediction of the absorption maxima of dyes, especially in the case of emphasizing computational cost.