Identification of Synthetic Organic Pigments (SOPs) Used in Modern Artist's Paints with Secondary Ion Mass Spectrometry with MeV Ions

Beyond Artists' Colors: A Spectral Reference Database for the Identification of β-Naphthol and Triarylcarbonium Colorants by MeV SIMS

β-Naphthol and triarylcarbonium colorants were often used by modern and contemporary artists in materials such as inks and paints. Their poor stability and ability to fade upon exposure to light make their identification in artworks crucial for planning exhibitions and preventive conservation. Secondary ion mass spectrometry with MeV primary ions (MeV SIMS) is necessary when analyzing synthetic organic colorants (SOCs) with similar molecular structures due to its advantages in high sensitivity and soft ionization, which causes a low fragmentation of organic molecules. In this work, we applied MeV SIMS with 5 MeV Si4+ to identify selected β-naphthol and triarylcarbonium colorants from the 19th/20th century Materials Collection kept at the Academy of Fine Arts Vienna. The collection contains SOCs from renowned companies, such as I.G. Farben and I.C.I., and serves as a unique source of reference materials in the analysis of artworks. Previous research on these colorants with X-ray fluorescence analysis (XRF), micro-Raman, and Fourier transform infrared (FTIR) spectroscopies failed in the case of colorant mixtures. Similar spectral features of the SOCs within one chemical class and their low concentrations in mixtures did not lead to their identification using these techniques. MeV SIMS detected molecular ions or protonated molecules in the positive-ion mode. In the negative-ion mode, the functional groups (NO2 - and SO3 -) of β-naphthol lakes/pigments and heteropolyacid species (WO3 - and MoO3 -) characteristic of triarylcarbonium toners were determined. The results demonstrate that MeV SIMS is highly effective for identifying β-naphthol and triarylcarbonium colorants in mixtures and distinguishing between pigments, toners, lakes, and dyes.

Review of recent advances on the use of mass spectrometry techniques for the study of organic materials in painted artworks

The study of painted artworks using scientific methods is fundamental for understanding the techniques used in their creation and their appropriate conservation. The ethical constraints involved in the handling of, and sampling from, these objects has steered recent developments in the field of Heritage science towards a range of new non-invasive/non-destructive spectroscopic techniques capable of providing important insights into their elemental or bulk chemical compositions. Due to the inherent complexities of heritage artefacts, however, their organic components are especially difficult to study in this way and their identification and degradation pathways are thus often best investigated using mass spectrometric (MS) techniques. The versatility, sensitivity and specificity of MS techniques are constantly increasing, with technological advances pushing the boundaries of their use in this field. The progress in the past ten years in the use of MS techniques for the analysis of paint media are described in the present review. While some historical context is included, the body of the review is structured around the five most widely used or emerging capabilities offered by MS. The first pertains to the use of spatially resolved MS to obtain chemical maps of components in cross-sections, which may yield information on both inorganic and organic materials, while the second area describes the development of novel sample preparation approaches for gas chromatography (GC)-MS to allow simultaneous analysis of a variety of components. The third focuses on thermally assisted analysis (either with direct MS or coupled with GC-MS), a powerful tool for studying macromolecules requiring zero (or minimal) sample pre-treatment. Subsequently, the use of soft ionisation techniques often combined with high-resolution MS for the study of peptides (proteomics) and other macromolecules (such as oligosaccharides and triglycerides) is outlined. The fifth area covers the advances in radiocarbon dating of painting components with accelerator MS (AMS). Lastly, future applications of other MS techniques to the study of paintings are mentioned; such as direct analysis in real time MS (DART-MS) and stable isotope ratio MS (IRMS). The latter, having proven its efficiency for the study of lipids in archaeological artefacts, is envisioned to become a valuable tool for this area, whereas DART-MS is already being utilised to study the surface composition of various museum objects. Rapid technological advances, resulting in increased sensitivity and selectivity of MS techniques, are opening up new approaches for paintings analysis, overcoming the fundamental hurdle of sample size available for destructive analysis. Importantly, while the last decade has seen proteomics applications come to the fore, this review aims to emphasise the wider potential of advanced MS techniques for the study of painting materials and their conservation.

Chemical Imaging of Organic Materials by MeV SIMS Using a Continuous Collimated Ion Beam

MeV SIMS is a type of secondary ion mass spectrometry (SIMS) technique where molecules are desorbed from the sample surface with ions of MeV energies. In this work, we present a novel system for molecular imaging of organic materials using a continuous analytical beam and a start trigger for timing based on the detection of secondary electrons. The sample is imaged by a collimated primary ion beam and scanning of the target with a lateral resolution of ∼20 μm. The mass of the analyzed molecules is determined with a reflectron-type time-of-flight (TOF) analyzer, where the START signal for the TOF measurement is generated by the secondary electrons emitted from a thin carbon foil (∼5 nm) placed over the beam collimator. With this new configuration of the MeV SIMS setup, a primary ion beam with the highest possible electronic stopping can be used (i.e., highest secondary molecular yield), and samples of any thickness can be analyzed. Since the electrons are collected from the thin foil rather than from the sample surface, the detection efficiency of secondary electrons is always the same for any type of analyzed material. Due to the ability to scan the samples by a piezo stage, samples of a few cm in surface size can be imaged. The imaging capabilities of MeV SIMS are demonstrated on crossing ink lines deposited on paper, a thin section of a mouse brain, and a fingerprint deposited on a thick Si wafer to show the potential application of the presented technique for analytical purposes in biology and forensic science.

Mass spectrometry in art conservation-With focus on paintings

Conservation of historic artifacts has been a multidisciplinary field from its very beginning. Traditionally, it has been and still is associated with the history of art. It applies knowledge from technical and basic sciences, adapting their solutions to its goals. At present, however, a new tendency is clearly emerging-scientific research is starting to play an increasingly important role not only as a service, but also by proposing new solutions both in the traditional conservation areas and in new areas of conservation activities. The above trend opens up new perspectives for the field of preservation of our heritage but may also create new threats. Therefore, the conservators' caution in introducing new technologies should always be justified; after all, they are responsible for the effects of any activities on the historic objects. This, quite selective review, discusses application of mass spectrometry techniques for the detection of various components that are important to the conservators of our heritage with particular focus on paintings. The text also contains some basic knowledge of technical details to introduce the methodology to a broader group of professionals.