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Improved methods for separation and quantitative determination of hydrocarbon types from gas oil have been developed, which were based on high-performance thin-layer chromatography with ultraviolet and fluorescence scanning densitometry using horizontal elution. One of the methods allows the separation, detection, and determination of alkanes and naphthenes to be carried out, using berberine-impregnated silica gel HPTLC plates, elution with n-hexane, and berberine-induced fluorescence detection at 365 nm. Another developed method allows total aromatics to be determined using silica gel HPTLC plates by elution with n-hexane and acetone, and UV detection. In turn, PACs over three aromatic rings can be determined on either silica gel or caffeine-impregnated silica gel HPTLC plates, elution with n-hexane, and selective detection using native fluorescence at 365 nm. Concentrations lower than 5 wt% can be determined using this technique. In addition, a technique for an efficient, baseline-resolved separation of a gas oil according to the number of aromatics rings (mono + di-, tri-, and polyaromatic compounds with more than three rings) is presented here. This technique involves a multistep elution on a mixed (silica gel and caffeine-impregnated silica gel HPTLC plate) using a counter-elution device, and UV detection.

Different methodologies, based on planar chromatography/detection with densitometry, have been used to analyse compound classes (also known as hydrocarbon group type (HGT)) in samples coming from petroleum and coal conversion. The main problem encountered to analyse these samples is the choice of standard: because of the high variability of the signal that is dependent of molecular structure, one pure hydrocarbon does not reflect the response of a mixture. However, a step based on thin layer chromatography at preparative scale has allowed the fractionation of sample to obtain its derived standards. After this, alkanes have been quantified by fluorescence in presence of berberine sulfate and aromatic compounds have been detected by UV after separation by high performance thin layer chromatography (HPTLC) at analytical scale. The feasibility of the planar chromatography has been tested. The quantitative results obtained for different samples are in agreement with those provided using well-established techniques in the petrochemical industry and the coal-derived product (CDP) analysis.

International audience; The present work investigates the potential of two analytical tools to ensure rapid and affordable analysis of tar, produced during biomass gasification. On one hand, high performance thin layer chromatography (HPTLC) provides quantitative and qualitative information on tar composition and on the other, UV spectroscopy allows rapid quantitative total polycyclic aromatic hydrocarbon (PAHs) determination. An original separation method, based on HPTLC coupled with UV and fluorescence detection, enables the resolution of non-volatile hydrocarbons into families from two to five aromatic rings, with a difference between condensed and non-condensed structures. The method uses a two-stage migration with ethyl acetate/n-hexane and n-hexane on RP-plates, at -23 degrees C. HPTLC is also used for tar quantification, by means of standard addition method after merging all the aromatic compounds in one peak. Thereafter, two approaches are proposed for UV quantification: the first, UV direct quantification, consists in determining the absorbance and concentration of a reference sample, which permits to calculate unknown tar concentration. The second, based on UV spectra deconvolution (UVSD), calculates tar concentration by UV deconvolution of selected standard spectra without the need of reference samples. Both approaches were applied on thirty-seven samples formed in three gasifiers, a Bubbling Fluidized Bed (BFB), an Internal Circulating Bubbling Fluidized Bed (ICBFB) and a Circulating Fluidized Bed (CFB). All the methods applied show a good agreement between the results obtained and the concentration of tar determined by HPLC/UV, the reference method.

6 Figures, 2 Tables, A large number of analytes, including non-fluorescent ones, can be sensitively detected by fluorescence scanning densitometry using silica gel HPTLC plates impregnated with a solution of coralyne cation. This is carried out by the variation, increase or decrease, that the corresponding analyte induces on native coralyne emission at a given excitation wavelength. A similar phenomenon was previously described for berberine cation, and Reichardt's dye probes. However, the sensitivity of coralyne in HPTLC detection of non-fluorescent, structurally different analytes (e.g., long-chain alkanes, alcohols, alkylbromides, neutral lipids) is superior to that of the above-mentioned probes. In this work, the analytical viability of this phenomenon for HPTLC detection using coralyne as a probe is explored, and fluorescent responses of a number of analytes on the coralyne system are rationalized in the light of a previously proposed model. This establishes that the resulting intensity for a probe in the presence of a given compound can be explained as a balance between radiative (contribution of non-specific interactions) and non-radiative processes (specific interactions), the latter producing fluorescence quenching. Experimental results and proposed model suggest that this phenomenon may be general for practically all kinds of analytes., The authors thank the Spanish Ministerio de Educación y Ciencia (MEC) and the Diputación General de Aragón (DGA) for financial support (projects CTQ2005-00227/PPQ and PM010, respectively).

6 Figuras., Many chemical compounds, including nonfluorescent ones, induce changes in the fluorescence spectra of certain probes, such as berberine cation and Reichardt's betaine, both in the absence and the presence of solvent, that affect almost exclusively emission intensity. In this work, the application of fluorescence detection by intensity changes (FDIC) to HPLC and TLC chromatographic systems with fluorescence detectors has been studied. FDIC detection is of special interest in detecting nonfluorescent analytes, either in HPLC or in TLC mode. It does not involve covalent interactions, and the dielectric permittivity (ε) of the medium plays an important role. The balance between nonspecific and specific interactions produces either an increase or a decrease in fluorescence intensity. Therefore, the influence of chromatographic conditions and chemical structure of analytes on the sign and magnitude of fluorescence peaks for sample detection in HPLC and TLC systems has been discussed. In general, probe nature and concentration determine response and detection sensitivity for a given sample in TLC and HPLC. As solubility and fluorescence properties in solvents determine the operating conditions for a FDIC probe in HPLC mode, nature and flows of mobile phase and solvent are important for chromatographic response and detection sensitivity., Authors thank the Spanish Ministerio de Ciencia y Tecnología (MCyT) and Ministerio de Educación y Ciencia for financial support (projects PPQ2001-2388 and CTQ2005-00227/PPQ). E.M.G. acknowledges MCyT for a grant.

A straight run gas oil has been hydrotreated with a commercial CoMo/Al2O3 catalyst, under variable conditions of severity, in order to yield processed products containing a variable amount of residual sulfur. These products have been characterized by simulated distillation, gas chromatography with sulfur-selective detection (GC−SCD), and thin-layer chromatography. The sulfur compounds have been grouped into distinct representative families. The rate constants for the reaction of desulfurization of the considered groups and the apparent rate order with respect to some individual sulfur compounds have been determined. The following hydrocarbon groups have been determined in the hydrotreated products by analytical thin-layer chromatography−densitometry: alkanes, cycloalkanes, total aromatics, and polyaromatic compounds (PACs). The straight run gas oil has been submitted to fractionation by preparative thin-layer chromatography, and the resulting fractions of alkanes, cycloalkanes, and aromatics have been ch...

Hydrocarbon group-type analysis (HGTA) is a common technique for characterization of complex mixtures derived from raw materials such as coal, petroleum, or biomass. In these and other, related, samples, trying to achieve extensive separation of all the components would be very difficult at least, and most of the relevant properties of the samples can be related to the amounts of the different types of hydrocarbon. Groups of interest depend mainly on the nature of the sample, and some kind of liquid chromatography is usually involved in the most common HGTA methods. Thin-layer chromatography (TLC) can nowadays usually be used instead of HPLC, resulting in several advantages in terms of speed, cost, and general convenience. Detection and quantification of the different peaks might involve the use of special equipment, e.g. in TLC-flame ionization detection (FID) methods, although it can also be accomplished by means of UV and fluorescence scanning densitometry. In this paper, we describe a series of TLC-ba...