Role of laser ablation–inductively coupled plasma–mass spectrometry in cultural heritage research: A review

Laser-based analytical techniques in cultural heritage science - Tutorial review

This tutorial review combines the fundamentals of the design and operation of lasers with their usage in applications related to conservation and cultural heritage (CH) science - as components of analytical devices for the study of the chemical composition of materials. The development of laser instruments and their fundamental physical background, including a short explanation of their properties and parameters, are briefly summarised, and an overview of different laser-based analytical techniques is given. The analytical techniques covered in this tutorial are divided into three groups based on their technical aspects and properties: (1) vibrational spectroscopy, (2) elemental analysis, and (3) different molecular mass spectrometric techniques.

Artefact Profiling: Panomics Approaches for Understanding the Materiality of Written Artefacts

This review explains the strategies behind genomics, proteomics, metabolomics, metallomics and isotopolomics approaches and their applicability to written artefacts. The respective sub-chapters give an insight into the analytical procedure and the conclusions drawn from such analyses. A distinction is made between information that can be obtained from the materials used in the respective manuscript and meta-information that cannot be obtained from the manuscript itself, but from residues of organisms such as bacteria or the authors and readers. In addition, various sampling techniques are discussed in particular, which pose a special challenge in manuscripts. The focus is on high-resolution, non-targeted strategies that can be used to extract the maximum amount of information about ancient objects. The combination of the various omics disciplines (panomics) especially offers potential added value in terms of the best possible interpretations of the data received. The information obtained can be used to understand the production of ancient artefacts, to gain impressions of former living conditions, to prove their authenticity, to assess whether there is a toxic hazard in handling the manuscripts, and to be able to determine appropriate measures for their conservation and restoration.

Characterization of fresh PM deposits on calcareous stone surfaces: Seasonality, source apportionment and soiling potential

Particulate matter (PM) pollution is one of the major threats to cultural heritage outdoors. It has been recently implied that organic aerosols will prevail over inorganic carbon particulates in the future, changing the main mechanisms of damage caused by poor air quality to calcareous heritage in particular. We studied fresh particulate deposits on marble and limestone surfaces exposed to urban air in sheltered and unsheltered configurations. Due to different air pollution sources in different seasons, the amount and composition of surface deposits varied throughout the year. The main and most constant contributor to PM_2.5 (particles smaller than 2.5 μm) were primary traffic emissions (30 %), followed by secondary formation of acidic inorganic aerosols, such as sulphate in summer and nitrate in winter (33 % altogether), and seasonal biomass-burning emissions (14 %). Although biomass burning is the major source of primary organic aerosols including the light-absorbing fraction that prevailed over black carbon (BC) in colder months (up to 60 % carbonaceous aerosol mass), we show that surface darkening causing the soiling effect is still governed by the minor BC fraction of atmospheric aerosols, which remained below 20 % of the carbonaceous aerosol mass throughout the year. This, however, can change in remote environments affected by biomass-burning emissions, such as winter resorts, or by rigorous BC mitigation measures in the future. In the short run, sheltered positions were less affected by different removal processes, but we show that surface deposits are not simply additive when considering longer periods of time. This must be taken into account when extrapolating surface accumulation to longer time scales.

Quantitative Determination of the Surface Distribution of Supported Metal Nanoparticles: A Laser Ablation–ICP–MS Based Approach

A laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) based method is proposed for the quantitative determination of the spatial distribution of metal nanoparticles (NPs) supported on planar substrates. The surface is sampled using tailored ablation patterns and the data are used to define three-dimensional functions describing the spatial distribution of NPs. The volume integrals of such interpolated surfaces are calibrated to obtain the mass distribution of Ag NPs by correlation with the total mass of metal as determined by metal extraction and ICP–MS analysis. Once this mass calibration is carried out on a sacrificial sample, quantifications can be performed over multiple samples by a simple micro-destructive LA–ICP–MS analysis without requiring the extraction/dissolution of metal NPs. The proposed approach is here tested using a model sample consisting of a low-density polyethylene (LDPE) disk decorated with silver NPs, achieving high spatial resolution over cm2-sized samples and very high sensitivity. The developed method is accordingly a useful analytical tool for applications requiring both the total mass and the spatial distribution of metal NPs to be determined without damaging the sample surface (e.g., composite functional materials and NPs, decorated catalysts or electrodic materials).

Laser-induced breakdown spectroscopy in heritage science

Laser-induced breakdown spectroscopy (LIBS) is a versatile analytical technique that can be used to probe the elemental composition of materials in diverse types of heritage samples, objects or monuments. The main physical principles underlying LIBS are presented along with analytical figures of merit and technical details concerning instrumentation. In practice, LIBS analysis does not require any sample preparation and the technique is nearly non-invasive, offering close to microscopic spatial resolution and the possibility for depth profile analysis. These features are, at present, available in a number of compact or transportable instruments that offer versatility and enable the use of LIBS for the analysis of a broad variety of objects/samples at diverse locations and this can be highly valuable at several stages of archaeological investigations and conservation campaigns. Representative examples are presented indicating how LIBS has been used to obtain compositional information for materials in the context of archaeological science, art history and conservation.

Inorganic mass spectrometry

Inorganic mass spectrometry has been used as a well-known analytical technique to determine elemental/isotopic composition of very diverse materials, based on the different mass-to-charge ratios of the ions produced in a specific source. In this case, two mass spectrometric techniques are explained and their analytical properties discussed: inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionisation mass spectrometry (TIMS), since they are the most used in art and archaeological material studies. Both techniques combine advantageous analytical properties, like low detection limits, low interferences and high precision. The use of laser ablation as sample introduction system in ICP-MS allows to avoid sample preparation and to perform good spatial-resolution analysis. The development of new instruments, improving the mass separation and the detection of the ions, specially multicollection detectors, results in high-precision isotopic analysis. A summary of the important applications of these mass spectrometric techniques to the analysis of art and archaeological materials is also highlighted.

A powerful tool for assessing distribution and fate of potentially toxic metals (PTMs) in soils: integration of laser ablation spectrometry (LA-ICP-MS) on thin sections with soil micromorphology and geochemistry

The dynamic behavior and inherent spatial heterogeneity, at different hierarchic levels, of the soil system often make the spatial distribution of potentially toxic metals (PTMs) quite complex and difficult to assess correctly. This work demonstrates that the application of laser ablation spectrometry (LA-ICP-MS) to soil thin sections constitutes an ancillary powerful tool to well-established analytical methods for tracing the behavior and fate of potential soil contaminants at the microsite level. It allowed to discriminate the contribution of PTMs in distinct soil sub-components, such as parent rock fragments, neoformed, clay-enriched or humified matrix, and specific pedogenetic features of illuvial origin (unstained or iron-stained clay coatings) even at very low contents. PTMs were analyzed in three soil profiles located in the Muravera area (Sardinia, Italy), where several, now abandoned mines were exploited. Recurrent trends of increase of many PTMs from rock to pedogenic matrix and to illuvial clay coatings, traced by LA-ICP-MS compositional data, revealed a pedogenetic control on metal fractionation and distribution, based on adsorption properties of clay minerals, iron oxyhydroxides or organic matter, and downprofile illuviation processes. The main PTMs patterns coupled with SEM-EDS analyses suggest that heavy metal-bearing mineral grains were sourced from the mine plants, in addition to the natural sedimentary input. The interplay between soil-forming processes and geomorphic dynamics significantly contributed to the PTMs spatial distribution detected in the different pedogenetic horizons and soil features.

Critical assessment of the elemental composition of Corning archeological reference glasses by LA-ICP-MS

Corning archeological reference glasses A, B, C, and D have been made to simulate different historic technologies of glass production and are used as standards in historic glass investigations. In this work, nanoseconds (193, 266 nm) and femtosecond (800 nm) laser ablation were used to study the elemental composition of Corning glasses using laser ablation inductively coupled plasma mass spectrometry. The determined concentrations of 26 oxides (Li₂O, B₂O₃, Na₂O, MgO, Al₂O₃, SiO₂, P₂O₅, K₂O, CaO, TiO₂, V₂O₅, Cr₂O₃, MnO, Fe₂O₃, CoO, NiO, CuO, ZnO, Rb₂O, SrO, ZrO₂, SnO₂, Sb₂O₅, BaO, PbO, Bi₂O₃) are compared with values reported in the literature. Results show variable discrepancies between the data, with the largest differences found for Cr₂O₃ in Corning A; Li₂O, B₂O₃, and Cr₂O₃ in Corning B; and MnO, Sb₂O₅, Cr₂O₃, and Bi₂O₃ in Corning C. The best agreement between the measured and literature values was found for Corning D. However, even for this reference, glass re-evaluation of the data was necessary and new values for PbO, BaO, and Bi₂O₃ are proposed.

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