Über die Wahl der Lösungsmittelsysteme bei der papierchromatographischen Trennung organischer Verbindungen

Zusammenfassung An praktischen Beispielen wurde gezeigt, in welcher Weise die Trennung organischer Verbindungen mittels Papierchromatographie erzielt werden kann. Man ist nicht auf einige bewährte Lösungsmittel systeme allein angewiesen, sondern kann von Fall zu Fall systematisch neue und geeignete Systeme benützen. Es hat sich bewährt, sich nach den elementaren Löslichkeitsregeln für organische Stoffe zu richten, unter der Voraussetzung, daß die zu chromatographierende Verbindung in der stationären Phase gut, in der mobilen Phase dagegen weniger löslich ist. Durch Änderung der stationären Phase (Wasser, nicht wäßriges, polares Lösungsmittel, nicht polares Lösungsmittel) oder der Polarität und Zusammensetzung der mobilen Phase kann man das Wandern der Flecke am Chromatogramm beeinflussen, beliebige R_fWerte erhalten und in vielen Fällen auch eine beliebige Reihenfolge der Verbindungen am Chromatogramm erzielen.Da die Löslichkeit organischer Verbindungen von intermolekularen Kräften abhängig ist, erscheint das Problem im Zusammenhang mit strukturellen Einflüssen sehr kompliziert und muß für jeden Fall auf eigene Weise gelöst werden. Die Löslichkeitseigenschaften können weiter durch Benutzung reaktiver Lösungsmittel beeinflußt werden, die z. B. die Verbindungen in wasserlösliche Salze überführen können. Dabei ist an die möglichen Komplikationen, die bei ionisierbaren Verbindungen durch Dissoziation und Hydrolyse entstehen können, zu achten.Von den Hauptfaktoren, die eine Trennung ermöglichen können, seien die folgenden erwähnt: funktionelle Gruppen, ihre Anzahl, Polarität, gegenseitige Stellung, bzw. ihre Basizität oder Azidität, C-Atomanzahl in homologen Verbindungen, inter- und intramolekulare Wasserstoffbindungen, sterische Faktoren u. a. Es ist dann von der Art des gewählten Lösungsmittelsystems abhängig, welche der genannten Faktoren im Vordergrund stehen und welche beseitigt werden.Wenn die Löslichkeitsunterschiede der zu trennenden Stoffe zu gering sind, um gute Trennungen zu ermöglichen, ist es zweckmäßig, die Verbindungen in solche Derivate zu überführen, deren Strukturunterschiede größer sind.

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Summary Practical examples are given to show how organic compounds can be separated by means of paper chromatography. The operator is not limited to tested solvent systems, but can use new suitable systems as the occasion demands. It has been found best to abide by the elementary rules of solubility of organic compounds, provided the compound to be chromatographed is quite soluble in the stationary phase but less soluble in the mobile phase. By altering the stationary phase (water, nonaqueous, polar solvent, non-polar solvent) or the polarity and composition of the mobile phase, the migration of the stains in the chromatogram can be influenced, selectedR _f -values can be obtained, and in many cases it is also possible to secure a desired succession of the compounds on the chromatogram.Since the solubility of organic compounds depends on intermolecular forces, the problem in connection with structural influences appears very complicated and must be solved individually for each case. Moreover, the solubility characteristics can be affected by using reactive solvents; for instance, the compounds can be converted into water soluble salts. Under such circumstances, sight must not be lost of the complications which may arise because of the dissociation and hydrolysis of ionizable compounds. The following are among the chief factors, which may make a separation possible: functional groups, their number, polarity, relative position, their basicity or acidity, C-atom number in homologous compounds, inter- and intramolecular hydrogen bonds, steric factors, etc. It then depends on the type of solvent system selected, which of these factors are predominant and which can be neglected or eliminated.If the solubility differences are too slight to permit good separations, the compounds to be separated should, if possible, be converted into derivatives whose structural differences are more pronounced.

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Résumé Des exemples pratiques montrent comment il est possible d'effectuer la séparation de combinaisons organiques par Chromatographie sur papier. Il n'est pas uniquement fait appel à des systèmes de solvants éprouvés mais, dans certains cas, de nouveaux systèmes appropriés sont systématiquement utilisés.Il s'est avéré satisfaisant de faire appel aux règles élémentaires de solubilité des substances organiques sous réserve que la combinaison à chromatographier soit suffisamment soluble dans la phase stationnaire et moins soluble dans la phase mobile. En faisant varier la phase stationnaire (eau, solvant non aqueux, solvant polaire, solvant non polaire) ou la polarité et la composition de la phase mobile, il est possible d'influencer la migration des taches du chromatogramme, d'obtenir des valeurs deR _f désirées et, dans de nombreux cas, d'obtenir les combinaisons dans un ordre déterminé sur le chromatogramme.La solubilité des combinaisons organiques étant fonction des forces intermoléculaires il en résulte que le problème se complique considérablement dans la mesure où l'on considère les influences structurelles et que chaque cas particulier doit recevoir une solution qui lui est propre. Les propriétés de solubilité peuvent en outre être influencées par l'emploi de solvants réactifs qui peuvent transformer, par exemple les combinaisons en sels solubles dans l'eau. Il faut alors tenir compte des possibilités de complications qui peuvent apparaître par dissociation et hydrolyse des combinaisons ionisables.Parmi les principaux facteurs qui permettent une séparation, il convient de mentionner les suivants: les groupes fonctionnels, leur nombre, leur polarité, leur position relative, ou encore leur acidité ou leur basicité, le nombre d'atomes de carbone de combinaisons homologues, les liaisons hydrogène inter- et intramoléculaires, les facteurs stériques, etc. Suivant la nature du système solvant choisi pourront alors varier les facteurs dont l'effet est prépondérant et ceux dont l'effet est nul. Lorsque les différences de solubilité des substances à séparer sont trop faibles pour permettre des séparations satisfaisantes, il est commode de transformer les combinaisons en dérivés dont les différences de structure soient plus importantes.

     

Voltammetric and X-ray diffraction analysis of the early stages of the thermal crystallization of mixed Cu,Mn oxides

Mixed Cu,Mn, Cu,Mn,Al, Cu,Mg,Mn, and Cu,Mg,Mn,Al oxides were obtained by calcination of amorphous basic carbonate (Cu,Mn oxides) or hydrotalcite-like precursors at 300–800 °C. The product composition was characterized by chemical analysis, XRD, and voltammetry of the microparticles. The XRD amorphous portion was detected indirectly by XRD and directly by voltammetry. Tenorite (CuO) and spinels were the main crystalline components of the oxide mixtures. The presence of Al shifted the onset of the crystallization of XRD-detectable tenorite and spinel to temperatures higher by 100–200 °C, and the presence of Mg shifted tenorite crystallization by 100 °C, but voltammetry was able to detect these phases even in XRD-amorphous or nanocrystalline calcines. Voltammetry is hence suitable for analysis of poorly crystalline oxides that can be used in heterogeneous catalysis.     

A Large Volume Injection Procedure for GC-MS Determination of PAHs and PCBs

A simple on-column injection system for large volume of liquid samples for the GC-MS determination of traces of PAHs and PCBs has been investigated. A deactivated fused silica capillary 20 m × 0.53 mm I.D. and 2 meters of an HP5 column (0.53 mm,1 m film thickness) were used as retention gaps. Injection volumes of 80 L for PAHs and 90 L for PCBs, allow determination of 5–50 ng L^–1 PAHs and 11–44 ng L^–1 PCBs in hexane solution with an RSD of < 10%. The method has been used for the determination of PCBs and PAHs in soil sample.     

Continuous chemiluminescence determination of formaldehyde in air based on Trautz-Schorigin reaction

A new continuous method for the determination of formaldehyde in air is described. A cylindrical wet effluent diffusion denuder is used for the collection of formaldehyde from air into a thin film of absorption liquid (distilled-deionized water). Formaldehyde in the denuder concentrate is on-line detected employing a chemiluminescence flow method based on a reaction of formaldehyde and gallic acid with hydrogen peroxide in an alkaline solution. The collection efficiency of formaldehyde is quantitative at the air flow rate of 0.5 L min⁻¹ (absorption liquid flow rate of 336 μL min⁻¹). The limit of detection (S/N = 3) is 0.60 μg m⁻³ HCHO (0.49 ppb). The calibration graph is linear up to 300 μg m⁻³ HCHO (244 ppb). The relative standard deviations of chemiluminescence method for 1 × 10⁻⁶ and 5 × 10⁻⁶ M HCHO are 2.87% and 1.49%, respectively. Acetaldehyde interferes negligible, other compounds do not interfere. The method was employed for formaldehyde measurement in ambient air. The comparison measurement illustrates the good agreement of results obtained by proposed method with those obtained by reference fluorimetric method.     

Study of carbon black obtained by pyrolysis of waste scrap tyres

Waste scrap tyres were thermally decomposed under various conditions. Decompositions were followed by the TGA method. Specific heating regimes were tested to obtain optimal structural properties of resulting pyrolytic carbon black produced by pyrolysis of scrap tyres and the process was characterized in temperature interval from 380 to 1,200 °C and heating rate 10, 20 and 50 °C min^?1 under nitrogen atmosphere. The original scrap tyres and pyrolytic carbon black were characterized by Raman and Fourier transform infrared spectroscopy methods. Textural properties were also determined. Effect of temperature and heating rate on process of pyrolysis of scrap tyres was observed. Shifting of temperature of maximum pyrolysis rate to lower value and spreading of DTG peak is caused by increasing heating rate. Temperature 570 °C was sufficient for total scrap tyres pyrolysis. Graphitic and disordered structure was distinguished in the formed carbon black by Raman spectroscopy. With increasing temperature, heating rate and weight loss, the amount of the graphitic structure was reduced at the expense of disordered structure. Destruction of nonporous scrap tyres and formation of porous structure took place at higher temperature. Porous carbon black is formed above 380 °C, specific surface area increased up to 88 m² g^?1 .     

Simultaneous determination of reduced and oxidized glutathione in tissues by a novel liquid chromatography-mass spectrometry method: application in an inhalation study of Cd nanoparticles

The paper presents the development of an advanced extraction and fast analytical LC MS/MS method for simultaneous analyses of reduced and oxidized glutathione (GSH and GSSG, respectively) in different animal tissues. The simultaneous determination of GSH and GSSG is crucial because the amount and ratio of both GSH and GSSG may be altered in response to oxidative stress, an important mechanism of toxicity. The method uses the derivatization of free thiol groups in GSH. Its performance was demonstrated for less explored tissues (lung, brain, and liver) in mouse. The combined extraction and analytical method has very low variability and good reproducibility, maximum coefficients of variance for within-run and between-run analyses under 8 %, and low limits of quantification; for GSH and GSSG, these were 0.2 nM (0.06 ng/mL) and 10 nM (6 ng/mL), respectively. The performance of the method was further demonstrated in a model experiment addressing changes in GSH and GSSG concentrations in lung of mice exposed to CdO nanoparticles during acute 72 h and chronic 13-week exposures. Inhalation exposure led to increased GSH concentrations in lung. GSSG levels were in general not affected; nonsignificant suppression occurred only after the longer 13-week period of exposure. The developed method for the sensitive detection of both GSH and GSSG in very low tissue mass enables these parameters to be studied in cases where only a little sample is available, i.e. in small organisms or in small amounts of tissue.     

Monitoring of the Proton Electrochemical Gradient in Reconstituted Vesicles: Quantitative Measurements of Both Transmembrane Potential and Intravesicular pH by Ratiometric Fluorescent Probes

Proteoliposomes carrying reconstituted yeast plasma membrane H⁺-ATPase in their lipid membrane or plasma membrane vesicles are model systems convenient for studying basic electrochemical processes involved in formation of the proton electrochemical gradient (Δμ_H ⁺) across the microbial or plant cell membrane. Δψ- and pH-sensitive fluorescent probes were used to monitor the gradients formed between inner and outer volume of the reconstituted vesicles. The Δψ-sensitive fluorescent ratiometric probe oxonol VI is suitable for quantitative measurements of inside-positive Δψ generated by the reconstituted H⁺-ATPase. Its Δψ response can be calibrated by the K⁺/valinomycin method and ratiometric mode of fluorescence measurements reduces undesirable artefacts. In situ pH-sensitive fluorescent probe pyranine was used for quantitative measurements of pH inside the proteoliposomes. Calibration of pH-sensitive fluorescence response of pyranine entrapped inside proteoliposomes was performed with several ionophores combined in order to deplete the gradients passively formed across the membrane. Presented model system offers a suitable tool for simultaneous monitoring of both components of the proton electrochemical gradient, Δψ and ΔpH. This approach should help in further understanding how their formation is interconnected on biomembranes and even how transport of other ions is combined to it.     

Thermal stability of nanocrystalline ε-Fe2O3

Thermal behavior of highly crystalline ε-Fe₂O₃ nanoparticles of different apparent crystallite sizes was characterized using thermogravimetry, differential thermal analysis, and analysis of evolved gas by mass spectrometry. Phase composition of the samples was monitored ex situ by X-ray powder diffraction. The results show that the thermal stability of this metastable iron oxide polymorph decreases with increasing particle size. For the particle diameter of 19(2) nm, the transformation temperature was equal to 794(5) °C, while for 28(2) nm only 755(10) °C. Surface of the nanoparticles contained adsorbed water and carbon dioxide. Elimination of these species proceeds in two steps. Water is removed at temperatures below 200 °C and CO₂ in the temperature range between 200 and 450 °C.     

Asymmetric deformation of bubble shape: cause or effect of vortex-shedding?

Two perpendicular projections of rising bubbles were observed in counter-current downstream diverging flow. Evidently, the bubbles did not enter the boundary layer at the channel wall and a plug liquid flow assumption was acceptable in our experimental equipment. This confirmed that the experiment was appropriate for simulation of bubble rises in a quiescent liquid column. Recent data obtained by a high-speed camera permitted recording over a period of 60 s. Image analysis by a tailor-made program provided a time-series of quantities related to the position, size, and shape of bubbles. In addition to determination of the aspect ratio of the equivalent oblate ellipsoid, deviation from this shape was investigated in respect of the difference between the bubble’s centre of mass and the geometrical centre of bubble projection. Autocorrelation of the data indicated that the bubble inclination oscillated harmonically with a frequency of 5–10 Hz; cross correlation showed that the horizontal shift of the centre of mass, as well as the horizontal velocity, increased with increasing bubble inclination, and the vertical shift of the centre of mass increased with an increases in the absolute value of the bubble inclination. There is no significant phase shift in the oscillation of these quantities. The bulky bottom side of the bubbles is in accordance with the model of bubble oscillation induced by instability of the equilibrium of gravity and surface tension forces. The oscillation frequency dependence on surface forces (Eötvös number) is evident, while viscosity does not play a significant role in low-viscosity liquids. Therefore, vortex-shedding is more likely to be an effect of the oscillation and not its cause.     

Preparation and characterization of titania based nanowires

A new method for preparation of titania nanowires with diameter around 10 nm and length up to 2–3 μm is described. The precursor was prepared from sodium titanate by adding ethylene glycole (EG) and heating at temperature of 198°C for 6 h under reflux. The sodium titanate glycolate formed by this way aggregated into 1D nanostructures and was subsequently transformed into titania glycolate during a chemical treatment with 98% sulfuric acid. Titania nanowires with variable amount of anatase and rutile were prepared by heating to temperatures in the range 350–1000°C. The precursor as well as titania based samples were characterized by X-ray diffraction, Infrared spectroscopy, Scanning electron microscopy, High resolution transmission microscopy, Thermogravimetry, Differential thermal analysis, Evolved gas analysis and Emanation thermal analysis. The nitrogen adsorption/desorption was used for surface area and porosity determination. The photoactivity of the prepared titania samples was assessed by the photocatalytic decomposition of 4-chlorophenol in an aqueous slurry under UV irradiation of 365 nm wavelength.