Comparative study of extraction methods of silver species from faeces of animals fed with silver-based nanomaterials.

Extractions methods based on ultrapure water, tetramethylammonium hydroxide (TMAH), and tetrasodium pyrophosphate (TSPP) were applied to faeces collected from two in vivo experiments of pigs and chickens fed with a silver-based nanomaterial to study the fate and speciation of silver. For TMAH extraction, cysteine and CaCl2 were used to evaluate their stabilization effect on the silver forms. The analytical techniques single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS), hydrodynamic chromatography hyphenated to ICP-MS (HDC-ICP-MS) and asymmetric flow field flow fractionation coupled to ICP-MS (AF4-ICP-MS) were applied to the simultaneous detection of particulate and dissolved silver. Results have shown that water extraction was a suitable option to assess the environmental release of silver, with percentages of 3 and 9% for faeces of pigs and chickens, respectively. The use of TMAH extraction combined with SP-ICP-MS analysis was useful to characterize Ag-containing particles (less than 1%). Both stabilizers, cysteine and CaCl2, have a similar effect on silver nanoparticle preservation for chicken faeces, whereas cysteine-Triton was better for pig samples. In any case, silver extraction efficiency with TMAH was low (39-42%) for both types of faeces due to a matrix effect. TSPP followed by ICP-MS enabled the fractionation of the silver in the faeces, with silver sulphide (41%) and ionic silver (62%) being the most abundant fractions.

Improving the Detectability of Microplastics in River Waters by Single Particle Inductively Coupled Plasma Mass Spectrometry.

Detection of microplastics in environmental samples requires fast, sensitive and selective analytical techniques, both in terms of the size of the microparticles and their concentration. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) allows the detection of plastic particles down to ca. 1 µm and down to concentrations of 100 particles per mL. In SP-ICP-MS, detection of carbon-containing particles is hampered by the presence of other forms of carbon (carbonates, organic matter, microorganisms…). An acidic pre-treatment of river water samples with 10% (v/v) nitric acid for 24 h allowed the reduction of the presence of dissolved carbon to ultrapure water levels and the digestion of potential microorganisms in the samples, recovering polystyrene microparticles up to 80%. Carbon-containing particles were detected in most of the samples analysed from Spanish and French Pyrenean rivers. The presence of microplastics in these samples was confirmed by Raman microscopy and their morphology was defined by electron microscopy combined with energy-dispersive X-ray spectroscopy. The developed SP-ICP-MS method is suitable for the rapid screening of river waters for the presence of microplastics, which can then be analysed by inherently slower but more selective techniques (e.g., Raman microscopy).

How to trust size distributions obtained by single particle inductively coupled plasma mass spectrometry analysis.

Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is a technique widely used to obtain direct information about the number concentration and the size distribution of nanoparticles in liquid suspensions. However, its methods still lack clear quality control strategies to confirm the validity of the information derived from them. Only the detection of the complete size distribution of the nanoparticles in a sample over the size critical value ensures obtaining unbiased quantitative information, otherwise information should be restricted to report the presence of nanoparticles over a certain size and number concentration since their actual total number concentration is underestimated and the size overestimated. Under the latter conditions, data processing produces histograms showing the tails of the incomplete size distributions, although apparently, complete distributions can also be obtained when particle events are recorded as peaks, as reported here for the first time. The occurrence of these misleading situations must be critically evaluated for each SP-ICP-MS analysis. An approach, based on estimation of size critical values and successive dilutions, is proposed for the assessment of the validity of the quantitative information obtained, together with specific criteria for reconsidering the information that can be derived from those measurements. The approach was verified with different case studies and applied to the analysis of complex nanomaterials, confirming the validity of the reported information by comparison with other techniques. A calculation tool is also included to facilitate the estimation of size critical values under experimental conditions.

Analytical applications of single particle inductively coupled plasma mass spectrometry: a comprehensive and critical review.

Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) refers to the use of ICP-MS as a particle counting technique. When ICP-MS measurements are performed at very high data acquisition frequencies, information about (nano)particles containing specific elements and their dissolved forms can be obtained (element mass per particle, size and number and mass concentrations). As a result of its outstanding performance, SP-ICP-MS has become a relevant technique for the analysis of complex samples containing inorganic nanoparticles. This review discusses the maturity level achieved by the technique through the methods developed for the detection, characterisation and quantification of engineered and natural (nano)particles. The application of these methods in different analytical scenarios is comprehensively reviewed and critically discussed, with special attention to their current technical and metrological limitations. The emergent applications of SP-ICP-MS in the field of nanoparticle-tagged immunoassay and hybridization methods are also reviewed.

Evaluation of hydrodynamic chromatography coupled to inductively coupled plasma mass spectrometry for speciation of dissolved and nanoparticulate gold and silver.

In this study, hydrodynamic chromatography coupled to inductively coupled plasma mass spectrometry has been evaluated for the simultaneous determination of dissolved and nanoparticulate species of gold and silver. Optimization of mobile phase was carried out with special attention to the column recovery of the different species and the resolution between them. Addition of 0.05 mM penicillamine to the mobile phase allowed the quantitative recovery of ionic gold and gold nanoparticles up to 50 nm, whereas 1 mM penicillamine was necessary for quantitative recovery of ionic silver and silver nanoparticles up to 40 nm. The resolution achieved between ionic gold and 10-nm gold nanoparticles was 0.7, whereas it ranged between 0.31 and 0.93 for ionic silver and 10-nm silver nanoparticles, depending on the composition of mobile phase. Best-case mass concentration detection limits for gold and silver species were 0.05 and 0.75 µg L-1, respectively. The developed methods allowed the simultaneous detection of nanoparticulate and dissolved species of gold and silver in less than 10 min. Size determination and quantification of gold and silver species were carried out in different dietary supplements, showing good agreement with the results obtained by electron microscopy and total and ultrafiltrable contents, respectively. Due to the attainable resolution, the quality of the quantitative results is affected by the relative abundance of nanoparticulate and dissolved species of the element and the size of the nanoparticles if present.

Detection, size characterization and quantification of silver nanoparticles in consumer products by particle collision coulometry.

Silver nanoparticles (AgNPs) are widely used in industrial and consumer products owing to its antimicrobial nature and multiple applications. Consequently, their release into the environment is becoming a big concern because of their negative impacts on living organisms. In this work, AgNPs were detected at a potential of + 0.70 V vs. Ag/AgCl reference electrode, characterized, and quantified in consumer products by particle collision coulometry (PCC). The electrochemical results were compared with those measured with electron microscopy and single-particle inductively coupled plasma mass spectrometry. The theoretical and practical peculiarities of the application of PCC technique in the characterization of AgNPs were studied. Reproducible size distributions of the AgNPs were measured in a range 10-100 nm diameters. A power allometric function model was found between the frequency of the AgNPs collisions onto the electrode surface and the number concentration of nanoparticles up to a silver concentration of 1010 L-1 (ca. 25 ng L-1 for 10 nm AgNPs). A linear relationship between the number of collisions and the number concentration of silver nanoparticles was observed up to 5 × 107 L-1. The PCC method was applied to the quantification and size determination of the AgNPs in three-silver containing consumer products (a natural antibiotic and two food supplements). The mean of the size distributions (of the order 10-20 nm diameters) agrees with those measured by electron microscopy. The areas of current spikes from the chronoamperogram allow the rapid calculation of size distributions of AgNPs that impact onto the working electrode.

Size characterization and quantification of titanium dioxide nano- and microparticles-based products by Asymmetrical Flow Field-Flow Fractionation coupled to Dynamic Light Scattering and Inductively Coupled Plasma Mass Spectrometry.

A procedure for the size characterization and quantification of titanium dioxide (TiO2) nano- and microparticles by Asymmetric Flow Field-Flow Fractionation (AF4) coupled to Dynamic Light Scattering (DLS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is described. Different strategies for size characterization with size standards and the use of the DLS signal for the estimation of hydrodynamic diameters are evaluated. The procedure has been applied to the characterization of TiO2 nanoparticles in photocatalytic products and crab sticks (surimis), where TiO2 is present as E171 food additive. Sizes in the range of 50-90 nm and 160-170 nm were estimated in the different photocatalytic products by AF4-DLS, in good agreement with the sizes predicted by calibration versus SiO2 and polystyrene standards. In surimis, sizes between 140 and 350 nm were estimated by AF4-DLS, similar to those reported in literature for E171 additive. These results were also compared to those obtained by single particle ICP-MS, which allowed the detection of a nano-sized fraction of TiO2 present in the four surimis analyzed. Titanium contents in one of the photocatalytic products determined by AF4-ICP-MS was 16.86 ± 2.54 mg g-1, whereas the alkaline extraction followed by AF4-ICP-MS allowed the determination of TiO2 content in four surimis at concentration levels in the range of the µg g-1 (from 3.14 ± 0.10 to 14.55 ± 1.46 µg Ti g-1), with channel recoveries above 85% in all cases. The method has been validated by comparison with the Ti content determined by ICP-OES after microwaved assisted acid digestion of all the samples. The methodology proposed allows the complete quantification of the (nano)particulate forms of titanium in complex matrices together with their size characterization.

Wine markers in archeological potteries: detection by GC-MS at ultratrace levels.

The detection of organic residues that remain absorbed into the pores of ceramic artifacts constitutes a source of information regarding their management. Taking into account the poor conservation state of the potteries and the low amount of the organic tracers together with the main drawbacks to get the relevant information concerning different aspects of past societies, the detection of organic biomarkers is still an analytical challenge. In this work, an improved analytical methodology to maximize the recovery of organic markers related to wine in archeological ceramics is presented. The developed method consists on the extraction of wine-related organic compounds including tartaric acid, malic acid, fumaric acid, succinic acid, citric acid, and syringic acid by means of ultrasonic probe-assisted extraction (UPAE) followed by a preconcentration step by mixed-mode strong anion exchange and reversed-phase solid-phase extraction (SPE) and a derivatization step prior to analysis by means of gas chromatography-mass spectrometry (GC-MS). Finally, the method was applied to real archeological ceramic fragments (two dolia), suspected to have been used to store wine, together with organic residues found inside two amphorae from Zaragoza (Spain). Graphical abstract.

Probing some organic ukiyo-e Japanese pigments and mixtures using non-invasive and mobile infrared spectroscopies.

Non-invasive identification of organic colourants in paintings still remains a challenging issue, especially in the case of extremely thin layers of paint on printed paper such as Japanese ukiyo-e prints. Because prints are fragile artworks, various non-invasive analytical methods need to be employed. The present work focuses on results obtained by combining fibre optic reflectance spectroscopy in the near-infrared range (FORS NIR) with mid-infrared (MIR) spectroscopy. The first step consists of identifying spectroscopic marker bands typical of some organic pigments (indigo, gamboge, cochineal, turmeric, safflower, dragon's blood). Some reference printouts involving paper substrate, binder and pigments (seldom used or as mixtures) were then investigated in order to establish a straightforward way to extract the marker bands of the pigments. Some data post-treatments were applied to the spectra, such as spectral subtraction, in order to abstract the signal from overlapping bands originating from both substrate and binder, and second derivative calculation to emphasise the pigment marker bands' frequency positions. These data treatments turned out to be relevant to extract information on the organic pigments of interest, even within complex mixtures.

Comparison between non-invasive methods used on paintings by Goya and his contemporaries: hyperspectral imaging vs. point-by-point spectroscopic analysis.

The development of non-invasive techniques for the characterization of pigments is crucial in order to preserve the integrity of the artwork. In this sense, the usefulness of hyperspectral imaging was demonstrated. It allows pigment characterization of the whole painting. However, it also sometimes requires the complementation of other point-by-point techniques. In the present article, the advantages of hyperspectral imaging over point-by-point spectroscopic analysis were evaluated. For that purpose, three paintings were analysed by hyperspectral imaging, handheld X-ray fluorescence and handheld Raman spectroscopy in order to determine the best non-invasive technique for pigment identifications. Thanks to this work, the main pigments used in Aragonese artworks, and especially in Goya's paintings, were identified and mapped by imaging reflection spectroscopy. All the analysed pigments corresponded to those used at the time of Goya. Regarding the techniques used, the information obtained by the hyperspectral imaging and point-by-point analysis has been, in general, different and complementary. Given this fact, selecting only one technique is not recommended, and the present work demonstrates the usefulness of the combination of all the techniques used as the best non-invasive methodology for the pigments' characterization. Moreover, the proposed methodology is a relatively quick procedure that allows a larger number of Goya's paintings in the museum to be surveyed, increasing the possibility of obtaining significant results and providing a chance for extensive comparisons, which are relevant from the point of view of art history issues.

Detection, characterization and quantification of inorganic engineered nanomaterials: A review of techniques and methodological approaches for the analysis of complex samples.

The increasing demand of analytical information related to inorganic engineered nanomaterials requires the adaptation of existing techniques and methods, or the development of new ones. The challenge for the analytical sciences has been to consider the nanoparticles as a new sort of analytes, involving both chemical (composition, mass and number concentration) and physical information (e.g. size, shape, aggregation). Moreover, information about the species derived from the nanoparticles themselves and their transformations must also be supplied. Whereas techniques commonly used for nanoparticle characterization, such as light scattering techniques, show serious limitations when applied to complex samples, other well-established techniques, like electron microscopy and atomic spectrometry, can provide useful information in most cases. Furthermore, separation techniques, including flow field flow fractionation, capillary electrophoresis and hydrodynamic chromatography, are moving to the nano domain, mostly hyphenated to inductively coupled plasma mass spectrometry as element specific detector. Emerging techniques based on the detection of single nanoparticles by using ICP-MS, but also coulometry, are in their way to gain a position. Chemical sensors selective to nanoparticles are in their early stages, but they are very promising considering their portability and simplicity. Although the field is in continuous evolution, at this moment it is moving from proofs-of-concept in simple matrices to methods dealing with matrices of higher complexity and relevant analyte concentrations. To achieve this goal, sample preparation methods are essential to manage such complex situations. Apart from size fractionation methods, matrix digestion, extraction and concentration methods capable of preserving the nature of the nanoparticles are being developed. This review presents and discusses the state-of-the-art analytical techniques and sample preparation methods suitable for dealing with complex samples. Single- and multi-method approaches applied to solve the nanometrological challenges posed by a variety of stakeholders are also presented.

Field-emission scanning electron microscopy and energy-dispersive x-ray analysis to understand the role of tannin-based dyes in the degradation of historical wool textiles.

An innovative approach, combining field-emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDX) analysis, is presented to investigate the degradation mechanisms affecting tannin-dyed wool. In fact, tannin-dyed textiles are more sensitive to degradation then those dyed with other dyestuffs, even in the same conservation conditions. FESEM-EDX was first used to study a set of 48 wool specimens (artificially aged) dyed with several raw materials and mordants, and prepared according to historical dyeing recipes. EDX analysis was performed on the surface of wool threads and on their cross-sections. In addition, in order to validate the model formulated by the analysis of reference materials, several samples collected from historical and archaeological textiles were subjected to FESEM-EDX analysis. FESEM-EDX investigations enabled us to reveal the correlation between elemental composition and morphological changes. In addition, aging processes were clarified by studying changes in the elemental composition of wool from the protective cuticle to the fiber core in cross-sections. Morphological and elemental analysis of wool specimens and of archaeological and historical textiles showed that the presence of tannins increases wool damage, primarily by causing a sulfur decrease and fiber oxidation.

Microcharacterization of a natural blue pigment used in wall paintings during the Romanesque period in northern Spain.

In Romanesque wall paintings in Aragon (Spain), the pigment used for creating blue was a very characteristic mineral, aerinite, which came from local ores in the southern Pyrenees. Optical and scanning electron microscopy (SEM), with energy-dispersive X-ray (EDX) analysis, X-ray diffraction, and reflectance spectroscopy were used to make a detailed microcharacterization of this rare blue pigment in order to improve the knowledge of its composition and possible variability, from samples of medieval paintings and some mineral ores. New analytical data on the chemical composition of the blue pigment are reported here, together with the characterization of its microstructure, and the heterogeneity of the natural pigment made by the features of the ore itself. X-ray diffraction pattern and color parameters of the mineral ores are also included. The data obtained by SEM-EDX will assist identification of this pigment by electron microscopy. The natural variability in composition observed in the samples may be used to explain formation of the extracted mineral and to compare several ore sources. Connection of the ore composition with the pigments used in Romanesque wall paintings will help both provenance and attribution studies.

Positive and negative-mode laser desorption/ionization-mass spectrometry (LDI-MS) for the detection of indigoids in archaeological purple.

Laser-based ionization techniques have demonstrated to be a valuable analytical tool to study organic pigments by mass spectrometric analyses. Though laser-based ionization techniques have identified several natural and synthetic organic dyes and pigments, they have never been used in the characterization of purple. In this work, positive and negative-mode laser desorption/ionization mass spectrometry (LDI-MS) was used for the first time to detect indigoids in shellfish purple. The method was used to study organic residues collected from archaeological ceramic fragments that were known to contain purple, as determined by a classical high-performance liquid chromatography-based procedure. LDI-MS provides a mass spectral fingerprint of shellfish purple, and it was found to be a rapid and successful tool for the identification of purple. In addition, a comparison between positive and negative mode ionization highlighted the complementarity of the two ionization modes. On the one hand, the negative-ion mode LDI-MS showed a better selectivity and sensitivity to brominated molecules, such as 6,6'-dibromoindigo, 6-monobromoindigo, 6,6'-dibromoindirubin, 6- and 6'-monobromoindirubin, thanks to their electronegativity, and produced simpler mass spectra. On the other hand, negative-ion mode LDI-MS was found to have a lower sensitivity to non-brominated compounds, such as indigo and indirubin, whose presence can be established in any case by collecting the complementary positive-ion LDI mass spectrum.

Discovering the composition of ancient cosmetics and remedies: analytical techniques and materials.

This article reviews the analytical techniques and procedures used in the study of ancient cosmetics, therapeutic chemicals, and remedies found in historical and archaeological sites. Well consolidated techniques based on molecular and atomic spectroscopy, for example FT-IR, Raman, SEM-EDX, and XRD, and analytical procedures based on high-performance chromatography and mass spectrometry, for example GC-MS and HPLC-MS are reviewed. The advantages of recently introduced techniques based on synchrotron radiation and on direct mass spectrometric techniques are also discussed. The possibility of extracting information about composition, preparation techniques, and the degradation processes of ancient cosmetics, pharmaceutics, and ritual balms is analysed by use of several case studies.

Gas chromatography/mass spectrometry and pyrolysis-gas chromatography/mass spectrometry for the chemical characterisation of modern and archaeological figs (Ficus carica).

Gas chromatography/mass spectrometry (GC/MS) after alkaline hydrolysis, solvent extraction and trimethylsilylation, and analytical pyrolysis using hexamethyldisilazane (HMDS) for in situ derivatisation followed by gas chromatographic/mass spectrometric analysis (Pyrolysis-silylation-GC/MS) were used to investigate the hydrolysable and soluble constituents, and the polymerised macromolecules of an archaeological fig (Ficus carica) recovered in Zaragoza (Spain), as well as of modern figs. The main aim was to study the compositional alterations undergone by the fig tissues in a particular archaeological environment: the fig was in a vessel and covered by a layer of a mixture of orpiment and gypsum. A comparison between the GC/MS results from modern and archaeological figs revealed that degradative reactions took place, leading to the disappearance/depletion of reactive (unsaturated fatty acids) and sensitive compounds (phytosterols and triterpenes). Py-silylation-GC/MS data provided evidence of a significant degradation of the saccharide and lipid components of the fig tissue, which left a residue enriched in polyphenols and polyesters.

Chemical investigation on black pigments in the carved decoration of sixteenth century alabaster tombs from Zaragoza (Spain).

An analytical protocol based on optical microscopy (OM), scanning electron microscopy (SEM) observation, energy-dispersive X-ray (EDX) analyses, analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis (Py-silylation-GC/MS) and gas chromatography/mass spectrometry (GC/MS) after alkaline hydrolysis, solvent extraction and trimethylsilylation was used to study the origin and nature of black pigments from the carved inscriptions of several panels of two alabaster tombs dated from the mid-sixteenth century. Optical microscopy and SEM observation showed the presence of an amorphous very dark-brown substance, from translucent to opaque. EDX analyses revealed that the samples were mainly made up of C and O, thus highlighting the organic nature of the material used in the inscriptions. Py-silylation-GC/MS and GC/MS analyses provided detailed molecular compositions, highlighting the presence of a wide range of compound classes including diterpenoid acids, tricyclic abietanes, mid- and long-chain monocarboxylic fatty acids, n-alkanols and nalkanes. The pyrograms, the chromatographic profiles and the presence of characteristic biomarkers indicated that a mixture of pine pitch and beeswax had been used to make the black inscriptions.