Egg vs. Oil in the Cookbook of Plasters: Differentiation of Lipid Binders in Wall Paintings Using Gas Chromatography-Mass Spectrometry and Principal Component Analysis.

Wall paintings are integral to cultural heritage and offer rich insights into historical and religious beliefs. There exist various wall painting techniques that pose challenges in binder and pigment identification, especially in the case of egg/oil-based binders. GC-MS identification of lipidic binders relies routinely on parameters like the ratios of fatty acids within the plaster. However, the reliability of these ratios for binder identification is severely limited, as demonstrated in this manuscript. Therefore, a more reliable tool for effective differentiation between egg and oil binders based on a combination of diagnostic values, specific markers (cholesterol oxidation products), and PCA is presented in this study. Reference samples of wall paintings with egg and linseed oil binders with six different pigments were subjected to modern artificial ageing methods and subsequently analysed using two GC-MS instruments. A statistically significant difference (at a 95% confidence level) between the egg and oil binders and between the results from two GC-MS instruments was observed. These discrepancies between the results from the two GC-MS instruments are likely attributed to the heterogeneity of the samples with egg and oil binders. This study highlights the complexities in identifying wall painting binders and the need for innovative and revised analytical methods in conservation efforts.

Secret Recipe Revealed: Chemical Evaluation of Raw Colouring Mixtures from Early 19th Century Moravia.

An archaeological excavation in Prostejov (Czech Republic) revealed a workshop of a local potter with colourless, pink, and blue powders presumably used to produce faience/surface decoration. A comprehensive analytical study, which combined elemental and molecular analysis techniques, was performed to shed light on the chemical composition of these unique findings. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM EDX), inductively coupled-plasma mass spectrometry (ICP MS), flow injection analysis (FIA) with electrospray ionisation mass spectrometry (ESI MS), laser desorption ionisation mass spectrometry (LDI MS), and Raman spectroscopy were applied to reveal the elemental composition of the powders and identify the colouring agents in the pink and blue powders. The colouring agents in the pink powder were probably iron and the agent in the blue powder is Prussian blue. On top of that, it was also possible to determine the organic additives in these powders through pyrolysis gas chromatography with mass spectrometric detection (Py GC/MS), atmospheric solids analysis probe ion mobility mass spectrometry (ASAP IM MS), and LDI MS. The organic constituents were identified as plant resin, beeswax, and fats. These results point to the preparation of faience/pigment mixtures as oil paint.

Combination of electronically driven micromanipulation with laser desorption ionization mass spectrometry - The unique tool for analysis of seed coat layers and revealing the mystery of seed dormancy.

Electronically driven micromanipulation (EDM) with microscopic control was used as a novel tool for sample preparation prior to direct (matrix assisted) laser desorption/ionization mass spectrometric ((MA)LDI-MS) analysis of mature pea seed coat composition in defined layers. Microscissors were used for seed coat fragment shape adjustment, microtweezers for sample holding and "microjackhammer" Milling Pro for precise mechanical removing of cell layers in defined depths (2, 5 or 10 µm). These procedures circumvent the application of embedding media or enzymatic digestion of seed coat that would complicate mass spectra interpretation (presence of matrix signals, analyte signals enhancement or attenuation) and represent alternative for 3D metabolites profiling. In addition, microinjector was used to apply a solution on intact or micropeeled seed coat surface in nano-volumes, i.e. MALDI matrix and/or lithium salt, that provide improvement of signal of sugars. Utilization of EDM enabled optimization of matrix composition on a single small fragment of seed coat overcoming thus problems with biological (seed to seed) variability. LDI-MS data were studied by multivariate statistical analysis and significant metabolites in particular layers of seed coats were identified. Normalized intensities of signals (NS) of long-chain hydroxylated fatty acids (HLFA) on intact dormant pea genotype (JI64) seed coats were significantly higher than in their counterparts treated by micropeeling confirming HLFA accumulation in outermost layers (cutin). Fatty acids distribution differences between dormant and non-dormant genotypes were explored in detail. On the other hand, NS of sugar chains and particular polyphenols were significantly higher in micropeeled seed coats of studied dormant and non-dormant genotypes than in intact seed coats. Furthermore, combination of EDM with mass spectrometry imaging (MSI) allowed vertical profiling of metabolites in hilum (a place of former attachment of seed to maternal plant) and comparison of its composition with surrounding tissues. The obtained results contribute to the understanding of relations between seed coat chemical composition and physical seed dormancy.

Non-enzymatic electrochemical determination of cholesterol in dairy products on boron-doped diamond electrode.

Determination of cholesterol in food matrices is essential for quality control concerning the health of consumers. Herein, a simple electrochemical approach for cholesterol quantitation in dairy products is evaluated. The newly developed differential pulse voltammetric method using acetonitrile-perchloric acid mixture as a supporting electrolyte is statistically compared to GC-MS and HPLC-UV. Oxidation signals of cholesterol at +1.5 V and +1.4 V (vs. Ag/AgNO3 in acetonitrile) provide detection limits of 4.9 µM and 6.1 µM on boron-doped diamond and glassy carbon electrodes, respectively. A simple liquid-liquid extraction procedure from dairy products into hexane resulted in a recovery rate of (74.8 ± 3.8)%. The method provides results in close agreement (at a 95% confidence level) with GC-MS, while HPLC-UV resulted in a significant difference in estimated cholesterol concentrations for all samples. This newly developed method is a simpler, faster and cheaper alternative to instrumentally demanding MS-based methods and clearly outperforms HPLC-UV.