Thermal desorption of atmospheric organic pollutants enriched on charcoal

A technique of thermal vacuum desorption of charcoal, used in passive dosimeters to enrich organic pollutants of toxicological importance, is described. It combines the advantages of the classic procedure of using highly active charcoal followed by solvent desorption and the environmental one-step procedure of analyzing the whole thermally desorbed sample. For pollutants such as trichloroethylene, tetrachloroethylene, ether, benzene and ethanol, the recovery and reproducibility are satisfactory. The unexpected decomposition of halothane and ethylacetate at higher temperatures is caused by the catalytic activity of the charcoal, but this can be tolerated under constant operating conditions.

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Zusammenfassung Eine Methode zum Anreichem toxikologisch bedeutender organischer Luftverunreinigungen durch thermische Vakuumdesorption von Aktivkohle nach dem Einsatz in passiven Dosimetern wird beschrieben. Die Methode kombiniert die Vorteile der klassischen Prozedur unter Verwendung hochaktiver Kohle mit nachfolgender Desorption durch Lösungsmittel einerseits mit denen der Umwelt-Analyse der gesamten desorbierten Probe in einem Schritt andererseits. Für Luftverunreinigungen wie Trichlorethylen, Tetrachlorethylen, Ether, Benzen und Ethanol werden ausreichende Wiedergewinnung und Reproduzierbarkeit ermittelt. Die unerwartete Zersetzung von Halothan und Ethylacetat bei höheren Temperaturen wird auf die katalytische Wirkung der Aktivkohle zurückgeführt. Sie kann unter konstanten Versuchsbedingungen jedoch toleriert werden.

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Fast heavy ion induced photon emission from organic solids and plasma desorption mass spectrometry

Fission fragments from a ²⁵²Cf source have been used to study fast heavy ion induced desorption of ions and luminescence in the wavelength region 200–680 nm from samples of Csl, the amino acids valine, isoleucine and tyrosine, and of the peptide substance P. All samples emit photons under fast heavy ion bombardment. Most of the emission is confined to the near-UV region and within narrow time profiles. Analysis of the fast decay regions of the time profiles show that all the compounds have at least a fast and a slow decay component, both in the nanosecond region. The use of such narrow photon signals as start time markers for time-of-flight measurements (TOF) has been demonstrated. As the photon signal is derived directly from the desorption event it gives the true number of starts for a secondary ion TOF spectrum. Characteristics of the photon emission from a CsI target together with correlation studies between the desorbed secondary ions and the photon signal indicate that the light emission is from the bulk of the material and not correlated with the secondary ions.     

Thermal desorption comprehensive two-dimensional gas chromatography for in-situ measurements of organic aerosols

The complexity of organic composition and temporal variability of atmospheric aerosols presents an extreme analytical challenge. Comprehensive two-dimensional gas chromatography (GC x GC) has been used on time integrated filter samples to reveal the presence of thousands of individual organic compounds in aerosols, but without defining the temporal variability in composition ideal for providing information on source resolution and human exposure to specific pollutants. We hereby introduce a new instrument, 2D-TAG, which combines our in-situ thermal desorption aerosol GC (TAG) instrument with GC x GC allowing for dramatically improved separation of organics with automated measurements at hourly timescales.     

Thermal desorption analysis:

Experiments on water desorption from silicate glass powders of different chemical compositions were carried out by means of DSC. In order to establish the desorption energy distributions, a model of the heterogeneous surface was applied to the thermoanalytical desorption curves, and the results are discussed together with contact angle measurements on flat polished glass samples.The maxima in the desorption curves shift to lower temperature with increasing hydrophobic character; this is caused by divalent cations such as Pb²⁺, Ca²⁺ and Zn²⁺, while alkali metal ions are responsible for an increase in the hydrophilic behaviour.

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Zusammenfassung Wasserdesorptionsexperimente an Silikatglaspulvern unterschiedlicher Zusammensetzung wurden mittels DSC ausgeführt. Für die Berechnung von Desorptionsenergieverteilungen wurde ein Modell der heterogenen Oberfläche genutzt und zusammen mit Randwinkelmessungen an glatten, polierten Glasoberflächen diskutiert. Das Maximum der Desorptionskurven verschiebt sich mit wachsendem hydrophoben Verhalten nach tieferen Temperaturen, wofür divalente Kationen wie Pb²⁺ Ca²⁺ Zn²⁺ verantwortlich sind, während Alkaliionen das hydrophile Verhalten begünstigen.

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Thermal desorption of quasimolecular ions

The thermal desorption of [M + Alkali]⁺ quasimolecular ions from a heated metal surface is reported for some alkali salts of carboxylic acids and mixtures of alkali halides with a crown ether, glucose and adenosine. No quasimolecular ion could be detected from sucrose. With benzo[15]crown-5 the desorption of [M + Na]⁺ ions takes place even below the threshold temperature for thermionic emission of alkali ions. In addition, the desorption of intact [B(C₆H₅)₄]^? ions from a layer of NaB(C₆H₅)₄ is reported.     

Recombination radiation from organic solids

The recombination radiation from organic solids, defined as the light emission following the fusion of oppositely charged carriers into an electrically neutral state, is discussed as a phenomenon underlying the function of organic light-emitting diodes (LEDs). Its intensity and spectral range depend on the population and nature of the emissive states, which differ, in general, from those created using light. These differences are pointed out and shown to be a result of the reverse pathways of the mutual transformation of localized molecular excitons and coulombically-correlated charge-pair excited states formed either by photoexcitation or electron-hole recombination. Spectral features of the radiation produced by the recombination of statistically independent charge carriers are discussed in terms of two molecules-based excited states like excimers or electromers in single-component materials and exciplexes or electroplexes in multicomponent materials. Consequences for optical and electrical characteristics of organic LEDs are discussed and illustrated by examples. Progress in the fundamental and applied research may be expected based on properties of recombination-produced electronic excited states.     

Autowave exothermic organic synthesis in the mixes of organic solids

The autowave modes of organic exothermic synthesis in the mixes of organic solids were studied. A traveling wave of exothermic reaction of organic synthesis appeared in the mixes at local thermal ignition. Useful low‐molecular organic compounds having, at least, synthetic value were found out with good yields after the reactions. Autowave modes were observed in different classes of organic reactions – red‐ox, halogenation, protonation, acylation, imination etc. The possibility to organize the autowave modes is determined by the exothermic nature of the reaction (≥20 kJ/mol), phase condition and thermal stability of the reagents and products. Main peculiarities, kinetics and mechanisms of the reactions in autowave modes were investigated. The basic advantages of autowave exothermic synthesis in organic solids were analyzed.     

Infrared, surface-assisted laser desorption ionization mass spectrometry on frozen aqueous solutions of proteins and peptides using suspensions of organic solids

Surface-assisted, laser desorption ionization (SALDI) time-of-flight mass spectra of proteins and peptides have been obtained from bulk frozen aqueous solutions by adding solid organic powders to the solutions before freezing. Abundant analyte ions were obtained with a 3.28 µm Nd:YAG/OPO laser. 20 compounds were evaluated as solid additives, and 16 yielded protein mass spectra. Successful solids included compounds like pyrene, aspartic acid, and polystyrene. The best results were obtained with nicotinic acid and indole-2-carboxylic acid, which yielded protein mass spectra anywhere on the sample and with every laser shot. Compared with ultraviolet-matrix-assisted laser desorption ionization on the same instrument, cryo-IR-SALDI had a comparable detection limit (≈1 µM), a lower mass resolution for peptides, and a higher mass resolution for large proteins. Approximately 2500 cryo-IR-SALDI mass spectra were obtained from a single spot on a 0.3-mm-thick frozen sample before the metal surface was reached. About 0.1 nL of frozen solution was desorbed per laser shot. The extent of protein charging varied between the SALDI solids used. With thymine, myoglobin charge states up to MH ₁₂ ⁺¹² were observed. It is tentatively concluded that observed ions are preformed in the frozen sample.     

Water adsorption and desorption on microporous solids at elevated temperature

Summary An accurate gravimetric method was used to explore water adsorption/desorption isotherms between 105 and to 250°C for a number of synthetic and natural porous solids including controlled pore glass, activated carbon fiber monoliths, natural zeolites, pillared clay, and geothermal reservoir rocks. The main goal of this work was to evaluate water adsorption results, in particular temperature dependence of hysteresis, for relatively uniform, nano-structured solids, in the context of other state-of-the-art experimental and modeling methods including nitrogen adsorption, spectroscopy, neutron scattering, and molecular simulation. Since no single method is able to provide a complete characterization of porous materials, a combination of approaches is needed to achieve progress in understanding the fluid-solid interactions on the way to developing a predictive capability.     

Matrix-assisted laser desorption of neutral organic molecules

Results of initial investigations of matrix-assisted laser desorption (LD) of neutral molecules are presented. The investigations were performed using gramicidine D as the test molecule, since both the wavelength-dependent LD beharioor and the ionization and fragmentation behaviour of the pure material had been studied previously. Comparisons between previously reported results for the pure compound and the matrix mixtures used in these studies are made. The results show that, whereas no signal could be observed from the pure sample material at non-resonant desorbing wavelengths, addition of a strongly absorbing matrix to the sample initiated LD of abundant intact neutral sample molecules. The results are discussed in the light of previous studies of the LD mechanism and support an explosive, mechanically driven model for the LD process.     

Thermal desorption of hydrogen from carbon nanosheets

Carbon nanosheets are a unique nanostructure that, at their thinnest configuration, approach a single freestanding graphene sheet. Temperature desorption spectroscopy (TDS) has shown that the hydrogen adsorption and incorporation during growth of the nanosheets by radio frequency plasma-enhanced chemical vapor deposition are significant. A numerical peak fitting to the desorption spectra (300-1273 K) via the Polanyi-Wigner equation showed that desorption followed a second order process, presumably by the Langmuir-Hinshelwood mechanism. Six peaks provide the best fit to the TDS spectra. Surface desorption activation energies were determined to be 0.59, 0.63, and 0.65 eV for the external graphite surface layers and 0.85, 1.15, and 1.73 eV for desorption and diffusion from the bulk. In contrast to TDS data from previously studied a-C:H films [Schenk et al. J. Appl. Phys. 77, 2462 (1995)], a greater amount of hydrogen bound as sp(2) hybridized carbon was observed. A previous x-ray diffraction study of these films has shown a significant graphitic character with a crystallite dimension of L(a)=10.7 nm. This result is consistent with experimental results by Raman spectroscopy that show as-grown carbon nanosheets to be crystalline as commercial graphite with a crystallite size of L(a)=11 nm. Following TDS, Raman data indicate that the average crystallite increased in size to L(a)=15 nm.     

Nickel nanoparticles and solids using organic solvents

Nickel colloids were prepared by codeposition of the metal with several organic solvents: acetone, ethanol, 2-propanol, 2-methoxyethanol and 1,2-dimethoxyethane at 77 K. The stabilities of the colloids and fine powders were measured. The metallic films and active solids were obtained by evaporation under vacuum at room temperature. The Ni-2-methoxyethanol colloids are stable over three months at room temperature, and the UV-VIS absorption spectra of the most stable colloids were obtained. A chemical characterization of Ni solids was carried out by several techniques such as elemental analysis, FT-IR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry (TGA). The IR studies show the presence of the solvent in the solids, which was confirmed by microanalysis. From TGA, DSC, and TGA-FTIR the metal-solvent was studied. From TGA, the kinetic parameters of decomposition reaction were calculated using the Freeman and Carroll equations. Received: 6 June 2000 Accepted: 6 September 2000     

Thermal symmetry breaking transitions in NaCl-type solids

The four conditions of Landau's theory of symmetry and phase transitions have been applied to the NaCl-type structure to obtain the structures of crystalline solids that can result from continuous distortions or ordering processes.     

Frustrated organic solids display unexpected gas sorption

Between nonsorptive solvate and desolvate forms of p-tert-butylcalix[5]arene lies a frustrated crystalline region in which there is rapid sorption of gases. From sorption studies, we conclude that the frustrated form is porous and that the intermediate form represents a new type of material that was previously unrecognized by traditional gas sorption trends or ideals for other active systems.     

Thermal decomposition kinetics of solids from DDTA curves

It is shown that the activation energy for solid thermal decompositions which follow a first order kinetic equation can be determined in a very simple manner from a single derivative differential thermal analysis (DDTA) curve. The experimental results are in good agreement with those obtained by other workers.     

Thermal desorption of substances from an inhomogeneous surface

Conclusions An analysis was given of the thermal desorption equations for an inhomogeneous surface.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 204–205, January, 1967.     

Thermal desorption of substances from a homogeneous surface

Conclusions An analysis was made of the equation of thermal desorption for first-order reactions and a homogeneous surface.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 202–203, January, 1967.