Michel Sablier

Molecular criteria for discriminating museum Asian lacquerware from different vegetal origins by pyrolysis gas chromatography/mass spectrometry

This paper focuses on the identification of several chemical markers of vegetal species of Oriental lacquers with the aim at providing a methodology consistent with sampling restrictions necessarily applied in the field of cultural heritage. The method proposed is based on rapid and easy single step thermally assisted hydrolysis-methylation (THM) pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analysis that can be carried out with a minimum amount of matter (typically 10 μg for a sample collected on a museum or an archaeological object). The main contribution of this study is to provide multiple molecular criteria for discriminating the three Asian species used for making lacquers, namely Rhus verniciflua Stokes, Rhus succedanea and Melanorrhoea usitata. Because these trees grow in specific areas, identifying the species involved in ancient lacquer coatings also provides geobotanical data and fruitful information on the exchange networks and trading routes developed by ancient societies. With this purpose, a systematic study of all pyrolysis products of lacquer coatings was carried out on modern dried lacquer films from authentified provenance. It was demonstrated that the whole pyrolysis products play a significant role in identifying the vegetal species. The chemotaxonomic value of homologous series of alkanes, alkenes and benzene derivatives, rarely explored until now, was assessed. It was shown that the combination of data related to five distinct groups of pyrolytic markers (composition and/or distribution of alkanes, alkenes and benzene, alkenyl-, alkylcatechol and phenol derivatives) provided new strong criteria to establish vegetal origin and provenance of Asian artworks, even though they have been largely altered over time. Case studies of archaeological Chinese lacquered artefacts and Japanese Buddhistic altar were thereafter successfully investigated to address informative potential and efficiency of these criteria on ancient and degraded lacquer coatings.

Ion attachment mass spectrometry combined with infrared image furnace for thermal analysis: evolved gas analysis studies.

A well-established ion attachment mass spectrometer (IAMS) is combined with an in-house single-atom infrared image furnace (IIF) specifically for thermal analysis studies. Besides the detection of many chemical species at atmospheric pressure, including free radical intermediates, the ion attachment mass spectrometer can also be used for the analysis of products emanating from temperature-programmed pyrolysis. The performance and applicability of the IIF-IAMS is illustrated with poly(tetrafluoroethylene) (PTFE) samples. The potential of the system for the analysis of oxidative pyrolysis is also considered. Temperature-programmed decomposition of PTFE gave constant slopes of the plots of temperature versus signal intensity in a defined region and provided an apparent activation energy of 28.8 kcal/mol for the PTFE decomposition product (CF(2))(3). A brief comparison with a conventional pyrolysis gas chromatography/mass spectrometry system is also given.

Protonation thermochemistry of alpha-aminoacids bearing a basic residue.

The proton affinity (PA) and protonation entropy, ΔpS°, of glycine (Gly), 1, aspartic acid (Asp), 2, asparagine (Asn), 3, histidine (His), 4, lysine (Lys), 5, glutamic acid (Glu), 6, and glutamine (Gln), 7, have been reinvestigated by the extended kinetic method, using the “isothermal point” method and the orthogonal distance regression technique. The proton affinity values of α-amino acids bearing a basic residue (PA = 926.8, 965.2, 996.0, 993.9, 981.8 and 988.1 kJ mol−1 for 2–7, respectively) show significant deviation from the tabulated values. As expected from the effect of a strong intramolecular hydrogen bond in the protonated forms of these peculiar amino acids, negative protonation entropies are detected (ΔpS° = −36, −43, −37, −29, −95 and −55 J mol−1 K−1 for 2–7, respectively).

Application of the kinetic method to bifunctional bases: ESI tandem quadrupole experiments

Abstract The applicability of the kinetic method to the determination of the basicity of bidentate molecules has been assessed by considering several molecules M previously studied by equilibrium method (M=acetone (1), 1,3-propanediol (2), glycerol (3), 1,4-butanediol (4), 1,3-propanolamine (5), 1,4-butanolamine (6), 1,3-propanediamine (7) and 1,4-butanediamine (8)). Protonated adducts [MHBi]+ (where Bi is a reference base) were produced by electrospray ionisation and analysed by tandem quadrupole mass spectrometry. Application of the classical correlation of the natural logarithm of the ratio of peak intensities, ln([MH]+/[BiH]+), with either the proton affinities (PA) or the gas phase basicities (GB) of the reference bases Bi to deduce PA(M) or GB(M) has been examined. It is confirmed that only the use of several experiments at different collision energies (“extended” or “isothermal point” methods) may lead to meaningful results. Good agreement is observed between the PA(M) values tabulated or obtained from the isothermal point for molecule M = 1 and 5–8. However, the present PA values appear to be different from that obtained by equilibrium method in the case of diols 2–4. It is generally observed that the measured “apparent” protonation entropies of all the bifunctional molecules examined are significantly less than that obtained by equilibrium methods.

Proton Affinity and Heat of Formation of Vinyloxy [CH2CHO]. and Acetonyl [CH2COCH3]. Radicals

Frequently found in hydrocarbon oxidation and in the photochemistry of carbonyl compounds, the β-carbonyl radicals are of interest. The experimental proton affinities of the two title radicals have been determined from proton transfer reactions (as shown) monitored in an FT-ICR mass spectrometer. This led to an estimation of their heats of formation (1: 13±3; 2: -34±3 kJ mol(-1)). Ab initio molecular orbital calculations, up to the G2 level, confirmed these results.

Varying the radio frequency: a new scanning mode for quadrupole analyzers

This paper describes a new scanning mode for quadrupole mass spectrometers. In accordance with the theoretical equations of ion motion in a quadrupolar field, an alternative method of scanning is possible varying only the RF applied to the rods of the quadrupole, keeping constant the amplitude of the AC and DC potentials. First results are reported for a RF scanning range of 0.4‐1.1 MHz and an AC amplitude of approximately 250 V. # 1998 John Wiley & Sons, Ltd.

Low-Pressure Chemical Ionization in Ion Trap Mass Spectrometry:

This article presents the specificities of low-pressure chemical ionization in ion trap mass spectrometry. One main feature is the ability to perform chemical ionization with liquid reagents as readily as with “conventional” gases (methane, isobutane and ammonia). The reactivities and analytical applications of gas and liquid reagents are summarized from literature data and are compared when possible.

Identification and ecotoxicity of degradation products of chloroacetamide herbicides from UV-treatment of water

The widespread occurrence of chlorinated herbicides and their degradation products in the aquatic environment raises health and environmental concerns. As a consequence pesticides, and to a lesser degree their degradation products, are monitored by authorities both in surface waters and drinking waters. In this study the formation of degradation products from ultraviolet (UV) treatment of the three chloroacetamide herbicides acetochlor, alachlor and metolachlor and their biological effects were investigated. UV treatment is mainly used for disinfection in water and wastewater treatments. First, the chemical structures of the main UV-degradation products were identified using gas chromatography coupled with mass spectrometry and liquid chromatography-mass spectrometry. The main transformation reactions were dechlorination, mono- and multi-hydroxylation and cyclizations. The ecotoxicity of the mixed photoproducts formed by UV-treatment until 90% of the original pesticide was converted was compared to the toxicity of chloroacetamides using the green alga Pseudokirchneriella subcapitata, the crustacean Daphnia magna and the marine bacteria Vibrio fischeri as test organisms. UV-treatment of alachlor and metolachlor increased the toxicity compared to the parent compounds while an equal toxicity was found for photolysis products of acetochlor. This suggests that toxic photodegradation products are generated from chloroacetamides under UV-treatment. An important perspective of this finding is that the photolysis products are at least as toxic as the parent compounds.

Lithium ion attachment mass spectrometry for on-line analysis of trace components in air: direct introduction

Abstract Lithium ion attachment mass spectrometric method has been successfully applied for the real time, on-line continuous measurement of trace (ppb) organic compounds in air. The method is based upon the establishment of adducts with Li+ ions, which attach to most organic compounds in air but do not react with any of the major components of air. This paper describes the application of on-line, continuous analysis of volatile organic compounds in air using strawberries as a source of organic volatiles.

Sodium ion attachment reactions in an ion trap mass spectrometer

The capabilities of ion traps to perform attachment reactions with alkali cations using classical scanning sequences have been exploited here with an ion trap mass spectrometer equipped with an external ion source to generate the reagent Na(+) ions. Kinetic studies have shown that, as expected, the attachment efficiency is very high, near-collision efficiency, and illustrate how the present method is particularly well suited for ion trap mass spectrometers. The large adaptability of the experimental conditions suggests that a wide range of organic molecules, characterized by a large alkali ion affinity, could be readily detected even at low levels. Applications of sodium ion attachment reactions are illustrated by the detection and characterization of explosives and some of their correlated pyrolytic degradation products. Detection -limits for phthalate compounds are shown to reach the low ng range of injected samples, without any noticeable difficulties in the full scan mode of acquiring mass spectra. Copyright 2000 John Wiley & Sons, Ltd.