Pyrolysis comprehensive gas chromatography and mass spectrometry: A new tool to assess the purity of ancient collagen prior to radiocarbon dating.

Exogenous carbonaceous contaminants coming from sediments significantly bias the radiocarbon date of collagen samples extracted from archaeological bone and teeth. In this study, a new approach combining pyrolysis, comprehensive gas chromatography and mass spectrometry (Py-GC × GC/MS) was proposed to ensure their removal during the demineralization and bone collagen extraction. This approach permitted to identify hydrocarbon contaminants for archaeological samples from the Neolithic period, in 30-40 µg of collagen. The use of 2D GC improved importantly the separation, selectivity and resolution compared to 1D GC thus permitting to detect organic contaminants within the complex chromatograms issued from collagen pyrolysis. Moreover, efficiency of the extraction steps in collagen sample preparation for radiocarbon dating (acid and alkali treatments, filtration steps) could be evaluated for four different protocols on the basis of organic contaminant removal. Radiocarbon dating of the extracted collagen of four of the tested protocols corroborated the results of the Py GC × GC/MS data. This approach opens new perspectives for the use of comprehensive gas chromatography in the domain of archaeological sciences.

Analysis of the volatile organic matter of engine piston deposits by direct sample introduction thermal desorption gas chromatography/mass spectrometry.

This article establishes an alternative method for the characterization of volatiles organic matter (VOM) contained in deposits of the piston first ring grooves of diesel engines using a ChromatoProbe direct sample introduction (DSI) device coupled to gas chromatography/mass spectrometry (GC/MS) analysis. The addition of an organic solvent during thermal desorption leads to an efficient extraction and a good chromatographic separation of extracted products. The method was optimized investigating the effects of several solvents, the volume added to the solid sample, and temperature programming of the ChromatoProbe DSI device. The best results for thermal desorption were found using toluene as an extraction solvent and heating the programmable temperature injector from room temperature to 300 degrees C with a temperature step of 105 degrees C. With the use of the optimized thermal desorption conditions, several components have been positively identified in the volatile fraction of the deposits: aromatics, antioxidants, and antioxidant degradation products. Moreover, this work highlighted the presence of diesel fuel in the VOM of the piston deposits and gave new facts on the absence of the role of diesel fuel in the deposit formation process. Most importantly, it opens the possibility of quickly performing the analysis of deposits with small amounts of samples while having a good separation of the volatiles.

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 ß-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.

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.