Methodology for dyes purification by preparative bidimensional offline reversed-phase high-performance liquid chromatography separation based on mobile phase pH change: Case study of Justicia spicigera.

The extensive characterization of the natural dyes involves the purification of their colored compounds for their structural analysis and stability studies. As most natural compounds being ionizable, herein is presented the optimization of an easy and affordable preparative bidimensional offline reversed-phase high-performance liquid chromatography purification based on mobile phase pH change. At the analytical scale, several combinations of stationary phases and mobile phases at different pH values were investigated first. The orthogonality between the dimensions was quantitatively evaluated using the nearest-neighbor distance approach. The optimized separation method was transferred to the preparative scale for the successful isolation of two colored compounds from Justicia spicigera, a traditional dye plant from Central America. They were identified as perisbivalvine B (2-amino-8-hydroxy-7-methoxy-3H-phenoxazin-3-one) and one of its derivatives, also found in another tinctorial plant species, Peristrophe bivalvis growing in Asia.

Spectral characterisation of a traditional Mesoamerican dye: relationship between in situ identification on the 16th century Codex Borbonicus manuscript and composition of Justicia spicigera plant extract.

Characterisation of vegetal colourants in manuscripts is still a challenging task. Their identification using non-invasive techniques - since sampling is rarely possible - is valid only if there is evidence that the recorded signals are generated by compounds specific to the plant species. Otherwise, more extensive chemical characterisations are required to relate the non-invasive technique signals to the chemical composition of the dye extract and thus avoid misidentification. The case study of a traditional Mesoamerican dye found in the Codex Borbonicus is reported herein. The non-invasive identification of the colourant plant source and chemical characterisation of the coloured molecules were carried out through a multi-analytical technique approach. In situ Raman and UV-Vis emission fluorescence signals suggested the use of Justicia spicigera leaves to produce the brown paint layers of the manuscript. Analysis of the plant extract by liquid chromatography revealed that two compounds are mostly responsible for the colour, and these compounds were successfully isolated. Both contribute to the Raman spectra while only one of them is mainly responsible for the fluorescence recorded on Codex Borbonicus.

A Preliminary Study on the Differentiation of Linseed and Poppy Oil Using Principal Component Analysis Methods Applied to Fiber Optics Reflectance Spectroscopy and Diffuse Reflectance Imaging Spectroscopy.

This paper presents results from the examination of a set of experimental samples using fibre optic reflectance spectroscopy (FORS) and diffuse reflectance imaging spectroscopy in the short-wave infrared (SWIR) range, combined with statistical analysis of the data for the discrimination and mapping of poppy and linseed oil. The aim was to evaluate the efficacy of this non-invasive approach for the study of paint samples with a view to the application of the method for characterisation of the two drying oils in painted art. The approach allowed discrimination between the two drying oils based on FORS spectra and the hyperspectral cube, indicating the influence of the spectral region around 1700 nm on the statistical discrimination based on the anti-symmetric and symmetric first overtone stretching of methylenic CH2 groups. This method is being studied as a potential non-invasive method of organic analysis of oil types that have formerly been studied using gas chromatography-mass spectrometry (GC-MS), which requires micro-samples.

2D macro-XRF to reveal redacted sections of French queen Marie-Antoinette secret correspondence with Swedish count Axel von Fersen.

During the French Revolution, Marie-Antoinette, queen of France and wife of Louis XVI, maintained a highly secret correspondence with the Swedish count Axel von Fersen, her close friend and rumored lover. An unidentified censor later redacted certain sections of the exchanged letters. This presumably sensitive content has been puzzling historians for almost 150 years. We report on the methodology that successfully unraveled this historical mystery. X-ray fluorescence spectroscopy was used in macroscanning mode on the redacted sections. Specific data processing was applied to improve the legibility of the hidden writings (elemental ratios, statistical data reduction, multimodal images fusion, unmixing procedure, and image treatments). This methodology successfully revealed the redacted contents of eight letters, shedding new light not only on Marie-Antoinette and Fersen relationship but also on the author of the redactions. It will also be of great interest for other historical and forensic cases involving the disentanglement of superimposed multi-elemental materials.

Characterizing the Intrinsic Fluorescence Properties of Historical Painting Materials: The Case Study of a Sixteenth-Century Mesoamerican Manuscript.

Ultraviolet visible (UV-Vis) fluorescence spectroscopy is widely used to study polychrome objects and can help to identify the nature of certain materials when they present specific fluorescent properties. However, given the complexity of the stratified and heterogeneous materials under study, the characterization of an intrinsic fluorescence related to a given constituent (a pigment or a binder composing a paint layer for example) is not straightforward, and the recorded raw data need to be corrected for a number of effects that can influence the detected spectral distribution. The application of standard correction procedures to experimental fluorescence data gathered on the polychromatic surface of the Codex Borbonicus, a 16th-century Aztec manuscript, is described. The results are confronted to an alternate new methodology that is based on the hypothesis of transparent non-scattering paint layers. This second approach allows to establish more clearly the material origin of the detected emission and to discriminate apparent fluorescence (emitted by the substrate and transmitted through the paint layers) from actual intrinsic emission generated by the coloring materials under study. The results show that most of the various emission profiles detected in the paint layers of the manuscript actually originate from a unique fluorophore (composing the substrate) and should not be used to characterize the coloring materials.