Gas Chromatography – Mass Spectrometry of Binding Media from Early 20th Century Paint Samples from Arnold Schönberg’s Palette

Tubes of paint from the Arnold Schönberg Center, Vienna, have been investigated using gas chromatography – mass spectrometry. In total, 23 oil paint samples from paint tubes in different stages of dryness have been examined. The analyses have suggested that the principal painting medium in Schönberg’s palette is linseed oil, mixed with resinous compounds, essential oils, and beeswax, which have been simultaneously identified using off-line transmethylation with TMTFAH as a methylation reagent.     

Gas chromatography-mass spectrometric analysis of bonded long chain fatty acids in a single zebrafish egg by ultrasound-assisted one-step transmethylation and extraction

Changes in the level of lipid composition in a single zebrafish egg have been involved in biological responses to chemical exposures. In this paper, an one-step transmethylation of lipids and simultaneous extraction of resultant fatty acid methyl esters followed by gas chromatography-mass spectrometric analysis was developed for the identification of bonded long chain fatty acids in a single zebrafish egg. The efficiency of transmethylation under different experimental conditions has been investigated. Dried egg homogenates were directly mixed with either 0.5 M NaOH or 1% H₂SO₄ or 4% HCl solution of methanol and then an n-hexane solution was added on the top. Ultrasonication of this immiscible liquid-liquid-solid system produces high velocity impacts between solid particles and liquid phases and thus promotes mass transfer among phases. It was demonstrated that ultrasound irradiation has strong effect on the alkaline-catalyzed transmethylation of lipids but cannot significantly change the acid-catalyzed transmethylation of lipids. With the aid of ultrasonication, transmethylation can be combined with simultaneous extraction of the resultant fatty acid methyl esters into n-hexane phase. This approach simplifies the sample preparation procedure, shortens the reaction time but improves the efficiency of the transmethylation of lipids and reduces sample losses, especially for small size samples. It has been applied to determine bonded fatty acids in a single zebrafish egg. In total, 28 fatty acids from a single zebrafish egg have been identified reproducibly.     

Transmethylation of metals in aquatic systems

Transmethylation reactions between organometals and metal ions in aqueous solutions in biotic and abiotic systems, with and without the presence of sediment, were investigated. It was found that alkyllead compounds can transfer their alkyl groups to Sn(II) and Sn(IV) ions to form various methyltin compounds in biotic and abiotic systems. The presence of sediment enhanced the transmethylation reactions. Methyltin compounds do not transfer their methyl groups of Pb(II). Methylarsenic acids transfer their methyl groups to Sn(II) and Sn(IV) in an abiotic system, but not in a biotic system containing sediment. The strong adsorption of tin onto sediment was the reason for the non-availability of tin ions for methylation. Methylarsenic acids do not transmethylate Pb(II). Other alkyllead compounds, such as ethyllead and butyllead species were also able to transfer their alkyl groups to tin. When both trimethyllead and triethyllead species are present in the same system, only the individual monoalkyl tin species were formed in both the Sn(II) and Sn(IV) solutions. No mixed alkyltin was produced. The findings of this study suggest that alkyllead compounds, if present in the environment, could be potential methylating agents for the formation of other methylmetals, such as methyltins. Methyltin compounds have already been documented to methylate mercuric ions in aqueous solution. Thus the study of transmethylation reactions opens up a new area of research that is essential in predicting the fate of organometals in the environment.