Characterization of polycyclic aromatic hydrocarbons in shale oil by chromatography and fluorescence densitometry

Polycyclic aromatic hydrocarbons (6-, 5-, 4- and 3-ring) were characterized in several shale oil samples. Open-column, dry-column and thin-layer chromatography were used in the separation steps. Visible fluorescence from the separated components on chromatoplates was measured directly to obtain fluorescence profiles of the distribution on the chromatoplates. The methods developed are inexpensive, reproducible, and allow rapid characterization of polycyclic aromatic hydrocarbons in shale oil samples.     

Room-temperature phosphorescence and fluorescence of nitrogen heterocyclics adsorbed on silica gel chromatoplates

The room-temperature phosphorescence of benzof]quinoline and phenanthridine has been enhanced considerably by spotting HBr-ethanol solutions of the compounds onto silica gel chromatoplates. Acridine showed no room-temperature phosphorescence but gave very strong fluorescence on silica gel chromatoplates. The analytical aspects are discussed, and some evidence is provided for the interactions of the compounds with the substrate.     

Room-temperature phosphorescence of selecte aromatic carboxylic acids adsorbed on silica gel and polyacrylic acid—sodium chloride mixtures

Several aromatic carboxylic acids give room-temperature phosphorescence when adsorbed on silica gel chromatoplates that contain a polymeric binder. Terephthalic acid is used as a model compound to investigate the interactions with such chromatoplates and various polyacrylic acid sodium chloride mixtures. The results indicate that under some conditions, hydrogen bonding appears to be operative, whereas under other conditions room-temperature phosphorescence can be detected without hydrogen bonding interactions.     

Separation of nebramycin components by ion-exchange thin-layer chromatography

A thin-layer chromatographic method on chromatoplates coated with Dowex 50 × 8 ion-exchange resin, suitable for the separation of 5 nebramycin components, was developed.     

Trace metal analysis by combined thin-layer chromatography and reflectance spectroscopy

Traces of nickel, cobalt and copper are separated on chromatoplates and, after reaction with rubeanic acid, are determined quantitatively by diffuse reflectance spectroscopy ; 0.05 μg of the elements can be determined with a probable percentage error of 2 to 5%. Temperature stability, aging, and pH dependence of the chelates and chelating agents in the adsorbed state were investigated. The method is simple and could find routine application in geochemistry, food analysis, etc.     

Differential reflectance spectrophotometry-I High-reflectance method for determination of micro amounts of substances resolved on thin plates

The basic principles of differential high-reflectance spectroscopy are discussed from the standpoint of the determination of substances resolved on chromatoplates. Results obtained with the use of two systems, nickel dimethylglyoximate or copper neocuproinate adsorbed on cellulose, are used as illustrations. A graphical method for selecting the optimum concentration range for analysis and for determining the maximum accuracy attainable is also outlined. When contrasted with the conventional method of measuring reflectance, the technique promises substantially increased accuracy over a wider concentration range and seems particularly suited to the analysis of trace amounts of material.     

A simple semimicro cell for the measurement of spectral reflectance

The construction and method of employment of a simple cell suitable for the measurement of the spectral reflectance of semimicro samples, such as those removed from chromatoplates, are described. An attempt is also made to correlate the performance of the cell with current theories of reflectance spectroscopy using data obtained with a system consisting of Merck silica gel G and McCormick blue, a food dye.     

Quantitative Dünnschicht-Chromatographie

To avoid errors caused by irregularities of chromatoplates in quantitative TLC often double beam densitometers are used. This paper describes the simulation of different double beam instruments using a single beam scanner and digital computers, to obtain distinct data on the increase in accuracy. The relative standard deviations from a greater number of experiments are: single beam scanner 3–5%, double beam instrument 2–4% and dual wave-length scanner 2.5–4%.     

Cation analysis by thin-layer chromatography and reflectance spectroscopy : Part II. The determination of copper,nickel and zinc

A method has been developed whereby micro quantities of copper, nickel and zinc resolved on cellulose chromatoplates can be analyzed in situ by means of reflectance spectroscopy. Copper and nickel were determined in the presence of 11 other cations without any interference by employing neocuproine and dimethylglyoxime, respectively, as chromogenic reagents. In the case of zinc, the use of 3,3'-dimethyl-naphthidine was equally successful except in the presence of tin, cadmium and iron. Deviations to be expected when the procedure is employed routinely to determine nickel, copper and zinc, were estimated to be 2.1, 2.8 and 5.6%, respectively.     

Determination of benzo[a]pyrene in shale oil-by solid-surface fluorescence

A method has been developed for determining benzo[a]pyrene in shale oil by combining dry-column chromatography, thin-layer chromatography and fluorescence spectrometry. A two-step separation method was employed to isolate benzo[a]pyrene from shale oil. Benzo[a]pyrene was identified and determined by detecting its fluorescence directly from chromatoplates; as little as 0.06 ng can be detected. The limit of detection of benzo[a]pyrene in shale oil is ca. 1.2 ppm and the reproducibility of the method is ±2.6 ppm.     

Analytical and mechanistic aspects of the room-temperature fluorescence and phosphorescence of benzo(f)quinoline adsorbed on silica gel chromatoplates with humidified gases

The solid-matrix room-temperature fluorescence and room-temperature phosphorescence properties of benzo(f)quinoline adsorbed on silica gel chromatoplates were investigated over a wide range of humidities in N(2), air and O(2). Both neutral and acidic conditions were used and even at the highest relative humidity used, 93% relative humidity, the room-temperature fluorescence and phosphorescence intensities from benzo(f)quinoline were not totally quenched. However, in all experiments, the room-temperature phosphorescence was much more sensitive to humidity quenching than the room-temperature fluorescence. The results gave rather detailed information on quenching of the room-temperature fluorescence and phosphorescence in the different gases at a variety of humidities. It was possible to calculate the contribution to the percent decrease in luminescence due to moisture or a quenching gas. Thus, a more detailed assessment could be made about the quenching of moisture and individual quenching gases on the solid-matrix fluorescence and phosphorescence.     

Development of a HPTLC method for in-process purity testing of pentoxifylline

A HPTLC method for the separation and identification of pentoxifylline and related substances, impurities of reaction partners, and side reaction products has been developed using different mobile and stationary phases. For quantitative assay of possible by-products as impurities, LiChrospher RP-18 F254s chromatoplates, acetone-chloroform-toluene-dioxane (2:2:1:1 v/v) as a mobile phase, and detection at 275 nm were employed. Linearity (r > or = 0.997), recovery (86.5-115.5%), and determination limit (0.1-0.6%) were evaluated and found to be satisfactory. This method enables monitoring of the synthesis, as well as purity control of pentoxifylline-containing raw materials and pharmaceuticals.     

High-performance thin-layer chromatographic determination of six major ginsenosides in Panax ginseng

A densitometric determination of six major ginsenosides in Panax ginseng, separated by high-performance thin-layer chromatography (HPTLC), was optimized. Simple extraction and clean-up methods of the target constituents and the development of standardized conditions of chromatoplates with a quaternary-solvents system allowed an efficient saponins recovery from the plant material and their selective separation. After exposure of the chromatograms to thionyl chloride vapors and further heating, stable reaction products of ginsenosides, which showed absorption maxima at lambda=275 nm as well as a fluorescence (lambda(excitation)=366 nm, lambda(emission)=400 nm), allowed the application of a sensitive and reproducible method for their simultaneous determination. The method was validated by spiking the ginseng extracts with pure standards.     

Semiquantitative determination of thiourea,thiocyanate, and sulfide by circular thin layer chromatography

Summary A method for semiquantitative determination of thiourea, thiocyanate, and sulfide is described. It involves making circular spots or rings on chromatoplates using the circular thin layer Chromatographic apparatus. The method is based on sensitivity and specificity of spot reactions and comparison of the color intensity of a circular spot with that of sensitivity standards. The accuracy of the method is ± 5% and the procedure is rapid, simple and economical.

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Zusammenfassung Ein Verfahren zur halbquantitativen Bestimmung von Thioharnstoff, Thiocyanat und Sulfid wurde beschrieben. Es beruht auf der chromatographischen Herstellung kreisförmiger Flecken oder Ringe auf Dünnschichtplatten. Mit empfindlichen und spezifischen Tüpfelreaktionen wurden die Flecken gefärbt und die Farbintensität mit Standardproben verglichen. Die Genauigkeit beträgt ± 5%.

     

Semiquantitative determination of noble metals by circular thin-layer chromatography

Summary A semiquantitative method for the determination of rhodium, gold, ruthenium, platinum, osmium, palladium and copper is presented. It involves making circular spots or rings on chromatoplates using the circular thin-layer Chromatographie apparatus. The method is based on sensitivity and specificity of spot reactions and the comparison of the color intensity of a circular spot with that of a standard scale. The accuracy is ± 6% and the procedure is rapid, simple and economical.

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Zusammenfassung Ein halb quantitatives Verfahren zur Bestimmung von Rh, Au, Ru, Pt, Os, Pd und Cu wurde beschrieben. Es beruht auf der Anwendung der Dünnschicht-Kreis-Chromatographie mit Hilfe empfindlicher und spezifischer Tüpfelreaktionen, deren Farbintensität mit Standardreihen verglichen wird. Die Genauigkeit beträgt ± 6%. Das Verfahren ist rasch, einfach und sparsam.

     

Separation of methylated ribonucleosides on cation-exchange thin-layer chromatoplates

Summary Three simple TLC systems based on the commercially available cation-exchange chromatoplates (Fixion 50×8) are described for the separation of different mixtures of naturally occurring methylated ribonucleosides.Part X in the series Separation of nucleic acid bases, nucleosides and nucleotides on strong cation-exchange thin layers. For part IX, see J. Tomasz. J. Chromatogr., in press.     

Quantitative determination of drugs by in situ spectrophotometry of chromatograms for pharmacokinetic studies. I. Sulpiride and other benzamides, vincamine, naftazone (author's transl)

Assays are proposed for sulpiride and other benzamides, vincamine and naftazone in plasma (or blood) and urine with direct UV reflectance spectrophotometry on this are applied directly on TLC along with a calibration curve on each plate. Plasma (or total blood) samples are extracted, and an internal standard is added before aplication; slopes of the obtained calibration curves do not change significantly from plate to plate, thus allowing several determinations on the same plate. The sensitivity is 2 microgram in a 1-ml sample (amount applied 30 ng) for sulpiride and related compounds and about the same for vincamine. Naftazone is determined in plasma with simultaneous reflectance and transmittance spectrophotometric measurements at 520 nm on chromatoplates sprayed with lead acetate, the sensitivity reached is 10 ng in a 1-ml sample (amount applied 0.5 ng). For all drugs studied, the proposed techniques are specific, reliable and sensitive enough and can be used to perform pharmacokinetic studies in human or in animal after administration of doses in the therapeutic range.     

Thin-layer chromatographic detection and estimation of steroid sapogenins in fenugreek

Summary A thin-layer Chromatographic method was developed for the detection and estimation of the steroid sapogenins of fenugreek seeds and plant at its various stages of growth. It depends on the initial separation of the constituent sapogenins (diosgenin, tigogenin and gitogenin) effectively on silica gel and alumina chromatoplates (n-hexane/ethylacetate as solvent) followed by direct photometric estimation of each product separately with reference to a calibration curve. Errors of ± 6% were found with synthetic mixtures.

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Dünnschicht-chromatographischer Nachweis und Bestimmung von Steroidsapogeninen in BockshornkleeSteroidsapogenine. XIV

Zusammenfassung Das Verfahren wurde zur Untersuchung der Samen und der Pflanze (Trigonella foenum graecum L.) in verschiedenen Wachstumsstufen angewendet. Die Sapogenine (Diosgenin, Tigogenin und Gitogenin) wurden auf Dünnschichten aus Silicagel oder Aluminiumoxid mit Hilfe von n-Hexan/Äthylacetat-Gemischen getrennt und anschließend photometrisch mit Phosphormolybdänsäure direkt auf der Platte bestimmt. In synthetischen Gemischen wurden Fehler von ± 6% gefunden.

     

Enzymic Methylation of Ascorbigen and Demethylation of Its N-Methyl Derivative by Pseudomonas savastanoi pv. phaseolicola Bacteria

Biotransformation of ascorbigen and N-methylascorbigen as a model compound pair was studied in the presence of Pseudomonas savastanoi pv. phaseolicola bacterium cells. These compounds were separated from a methanolic mixture by using an overpressured layer chromatographic method. After saturation of the developed chromatoplates with the bacterial cell suspension, the composition of the chromatographic spots was analyzed by means of high performance liquid chromatography. Pattern recognition by independent multicategory analysis was used to compare of the retention behavior of the standard and putative ascorbigen and methylascorbigen, and to manage the analytical data. Results showed that ascorbigen was partially methylated and N-methylascorbigen was partially demethylated by the bacteria. Our new results confirm the former assumption that formaldehyde is formed by demethylation of the N-methyl group of methylascorbigen.

     

Unsymmetrical disulfide and sulfenamide synthesis via reactions of thiosulfonates with thiols or amines

The reactivity of thiosulfonates with nucleophilic reagents was investigated. When reactions of thiosulfonates with thiols were performed, unsymmetrical disulfides were obtained in excellent yields. This procedure could employ numerous aryl or alkyl thiols. On the other hand, reactions of thiosulfonates with amines proceeded in the presence of a copper catalyst. The procedure was performed efficiently in air, and afforded the corresponding sulfenamides.