EXPRESS: Landmark Publications in Analytical Atomic Spectrometry: Fundamentals and Instrumentation Development.

The almost-two-centuries history of spectrochemical analysis has generated a body of literature so vast that it has become nearly intractable for experts, much less for those wishing to enter the field. Authoritative, focused reviews help to address this problem but become so granular that the overall directions of the field are lost. This broader perspective can be provided partially by general overviews but then the thinking, experimental details, theoretical underpinnings and instrumental innovations of the original work must be sacrificed. In the present compilation, this dilemma is overcome by assembling the most impactful publications in the area of analytical atomic spectrometry. Each entry was proposed by at least one current expert in the field and supported by a narrative that justifies its inclusion. The entries were then assembled into a coherent sequence and returned to contributors for a round-robin review.

An invasive bivalve with the potential to reconstruct chronologies of geomarkers in a large South American basin.

The Sr/Ca and 87Sr/86Sr ratios are used as natural indicators (geomarkers) in fish to reveal migratory patterns, due to significant relationships between these ratios measured in the water and in the fish calcified structures (otoliths, bones). The aim of this study was to assess the potential use of the Limnoperna fortunei shell as a proxy for monitoring the spatial and temporal variability of Sr/Ca and 87Sr/86Sr in water. These ratios were compared in water samples and bivalve shells proceeding from eight sites of four hydrogeological regions of the La Plata Basin (Argentina and Uruguay), collected in two hydrological periods (winter and summer) in order to depict the pattern of geographical and temporal variability and to evaluate the relationship between both matrices. Significant positive linear relationships were found between shell edge and water for 87Sr/86Sr (R2 = 0.96-0.97, p < 0.005) and Sr/Ca (R2 = 0.83-0.86, p < 0.05) in summer and winter. Slopes did not differ significantly from 1 (p > 0.05) for 87Sr/86Sr, while they differed from 1 for Sr/Ca in both seasons (p < 0.05), indicating that the elemental ratio would be influenced by endogenous/exogenous factors. No significant seasonal differences were found for both natural tags (p > 0.05), except for the lower Uruguay River (87Sr/86Sr) and outer estuary (Sr/Ca). These results indicate that the L. fortunei shell could be a valuable tool for monitoring spatio-temporal variations in water 87Sr/86Sr. Shell Sr/Ca shows high potential utility as a geomarker in freshwater, but additional assessments are needed to understand the impact of temperature and growth on this ratio.

Peptide-Platinum(IV) Conjugation Minimizes the Negative Impact of Current Anticancer Chemotherapy on Nonmalignant Cells.

The relative success of platinum (Pt)-based chemotherapy comes at the cost of severe adverse side effects and is associated with a high risk of pro-oncogenic activation in the tumor microenvironment. Here, we report the synthesis of C-POC, a novel Pt(IV) cell-penetrating peptide conjugate showing a reduced impact against nonmalignant cells. In vitro and in vivo evaluation using patient-derived tumor organoids and laser ablation inductively coupled plasma mass spectrometry indicates that C-POC maintains robust anticancer efficacy while displaying diminished accumulation in healthy organs and reduced adverse toxicity compared to the standard Pt-based therapy. Likewise, C-POC uptake is significantly lowered in the noncancerous cells populating the tumor microenvironment. This results in the downregulation of versican, a biomarker of metastatic spreading and chemoresistance that we found upregulated in patients treated with standard Pt-based therapy. Altogether, our findings underscore the importance of considering the off-target impact of anticancer treatment on normal cells to improve drug development and patient care.

Long-term platinum-based drug accumulation in cancer-associated fibroblasts promotes colorectal cancer progression and resistance to therapy.

A substantial proportion of cancer patients do not benefit from platinum-based chemotherapy (CT) due to the emergence of drug resistance. Here, we apply elemental imaging to the mapping of CT biodistribution after therapy in residual colorectal cancer and achieve a comprehensive analysis of the genetic program induced by oxaliplatin-based CT in the tumor microenvironment. We show that oxaliplatin is largely retained by cancer-associated fibroblasts (CAFs) long time after the treatment ceased. We determine that CT accumulation in CAFs intensifies TGF-beta activity, leading to the production of multiple factors enhancing cancer aggressiveness. We establish periostin as a stromal marker of chemotherapeutic activity intrinsically upregulated in consensus molecular subtype 4 (CMS4) tumors and highly expressed before and/or after treatment in patients unresponsive to therapy. Collectively, our study underscores the ability of CT-retaining CAFs to support cancer progression and resistance to treatment.

Comparison of Mg/Ca concentration series from Patella depressa limpet shells using CF-LIBS and LA-ICP-MS.

The elemental composition of marine mollusk shells can offer valuable information about environmental conditions experienced by a mollusk during its lifespan. Previous studies have shown significant correlations between Mg/Ca concentration ratios measured on biogenic carbonate of mollusk shells and sea surface temperature (SST). Here we propose the use of Laser-Induced Breakdown Spectroscopy (LIBS) and the validation of the Calibration-Free LIBS (CF-LIBS) approach for the rapid measurement and estimation of Mg/Ca molar concentration profiles within Patella depressa Pennant, 1777 limpet shells. To achieve these objectives, results derived from CF-LIBS methodology are compared with those obtained from an established analytical technique for this purpose, such as Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Concentration series obtained with both methodologies show defined temporal patterns and reflect the season-of-capture in each specimen. The results evidence a significant correlation (R2 = 0.63-0.81) between CF-LIBS and LA-ICP-MS Mg/Ca molar concentration profiles within four live-collected P. depressa shells. Averaged error for the molar concentration estimated with CF-LIBS was lower than 10% in every specimen. The comparison between the results obtained from two techniques used in this study has allowed us to demonstrate for the first time that Mg/Ca molar concentration measured in biogenic carbonates were accurately inferred using CF-LIBS technique. The CF-LIBS approach validation represents great potential for the rapid and large-scale paleoenvironmental and archaeological analysis of this mollusk species, which is frequently found in archaeological sites.

White mullet Mugil curema population structure from Mexico and Brazil revealed by otolith chemistry.

The white mullet Mugil curema supports several fisheries in the neotropical region; nevertheless, the population structure is still elusive. The aim of this study was to assess the presence of adult management units and nursery areas from five sampling sites throughout the Gulf of Mexico and northern Brazil using otolith microchemistry. The Li/Ca, Na/Ca, Mn/Ca, Sr/Ca, Ba/Ca and Pb/Ca ratios were measured in otolith core (juvenile stage) and edge (adult stage) (N = 131) using laser ablation-inductively coupled plasma-mass spectrometry. Several ratios were significantly different between sampling sites for core and edge (P < 0.05). For otolith edge, permutational multivariate analysis of variance showed significant differences (P < 0.05) between all sampling sites from Mexico (except between Mecoacán and Tamiahua, P > 0.05) and between Mexico (pooled samples) and Brazil. Quadratic discriminant analyses showed jackknifed classification higher in the edge (66.6% and 99.5% for Mexico and Brazil plus Mexico, respectively) than in the core (46.3% and 76.5% Mexico and Brazil plus Mexico, respectively). The two cluster analyses based on the core microchemistry (Mexico and Brazil plus Mexico) produced three main clusters, which did not coincide with catchment areas. These results support the segregation of the M. curema adult life stages among several sampling sites from Mexico and Brazil; moreover, core analysis suggested that the nursery areas did not correspond to the capture sites or adults stocks.

Otoliths as indicators for fish behaviour and procurement strategies of hunter-gatherers in North Patagonia.

This study evaluates the potential use of archaeological otoliths of Genidens barbus (Cuvier and Valenciennes) as a tool to study fish behavior and hunter-gatherers procurement strategies on the North Patagonian coast. The studied samples come from the San Antonio archaeological locality dated at ca. 1000-800 14C yr BP (Late Holocene). To assess whether exposure to fire significantly affects the otolith Sr:Ca and Ba:Ca ratios, burned and unburned modern lapilli otoliths have been analyzed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry and no statistically significant differences were found between the results of both treatments. Core-to-edge chemical time series were carried out on ancient otoliths (ca. 1000 14C yr BP) in order to study the fish life history. Three amphidromous patterns were found for ancient samples. The capture environments and seasons inferred by the otolith edge chemistry and marginal increase, respectively, suggest a location in high salinity water (estuary and sea) in summer. Finally, to estimate the size of archaeological fish, a linear regression between total length and otolith length was constructed using 70 modern catfish otoliths. The size variability (358-610 mm) might indicate the use of non-selective capture techniques, probably nets, by hunter-gatherer groups.

An exploratory study of the potential of LIBS for visualizing gunshot residue patterns.

The study of gunshot residue (GSR) patterns can assist in the reconstruction of shooting incidences. Currently, there is a real need of methods capable of furnishing simultaneous elemental analysis with higher specificity for the GSR pattern visualization. Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-elemental analysis of the sample, requiring very small amounts of material and no sample preparation. Due to these advantages, this study aims at exploring the potential of LIBS imaging for the visualization of GSR patterns. After the spectral characterization of individual GSR particles, the distribution of Pb, Sb and Ba over clothing targets, shot from different distances, were measured in laser raster mode. In particular, an array of spots evenly spaced at 800µm, using a stage displacement velocity of 4mm/s and a laser frequency of 5Hz was employed (e.g. an area of 130×165mm2 was measured in less than 3h). A LIBS set-up based on the simultaneous use of two spectrographs with iCCD cameras and a motorized stage was used. This set-up allows obtaining information from two different wavelength regions (258-289 and 446-463nm) from the same laser induced plasma, enabling the simultaneous detection of the three characteristic elements (Pb, Sb, and Ba) of GSR particles from conventional ammunitions. The ability to visualize the 2D distribution GSR pattern by LIBS may have an important application in the forensic field, especially for the ballistics area.

Migration and brackish environment use of Prochilodus lineatus (Characiformes: Prochilodontidae) inferred by Sr:Ca ratio transects of otolith

The streaked prochilod, Prochilodus lineatus, represents the most important fishery in the La Plata Basin (South America). Our objective was to analyze brackish environment use by the streaked prochilod captured from Paraná and Uruguay rivers. To accomplish this, lapillus otolith sections were analyzed for Sr:Ca with laser ablation-inductively coupled plasma-mass spectrometry (LA ICP-MS) to infer habitat use of fish. To the interpretation of transects, a threshold that represents the transition between freshwater and brackish environments was calculated using the Sr:Ca ratio of the otolith edge of specimens captured in the first section of the La Plata Estuary (salinity ≥ 0.5 PSU). The percentage of fish using the estuary was higher in the Paraná (37%) than the Uruguay River (5%). Change-point analysis showed that fish entered the estuary between 1 and 3 times throughout life at a wide range of ages (0-15 years). These incursions had no obvious periodicity. This information should be integrated into future management actions, which should also be specific to each area since migration patterns differ between the major rivers of the basin.(AU)

El sábalo, Prochilodus lineatus, representa la pesquería más importante en la Cuenca del Río de la Plata (Sudamérica). Nuestro objetivo fue analizar el uso del hábitat estuarino del sábalo proveniente de los ríos Uruguay y Paraná. Para esto, se analizó la relación Sr:Ca en secciones de otolitos lapilli por ablación láser acoplada a espectrometría de masas con fuente de plasma de acoplamiento inductivo (LA ICP-MS) para inferir el uso de hábitat. Para interpretar las transectas, un umbral que representa la transición entre los ambientes de agua dulce y estuarino, fue calculado usando la relación Sr:Ca del borde del otolito de especímenes capturados en la primera sección del estuario del Plata (salinidad ≥0.5 UPS). El porcentaje de peces que usaron el estuario fue más elevado para el Paraná (37%) en relación al Uruguay (5%). El análisis de cambio puntual mostro que los individuos ingresan al estuario entre 1 a 3 veces a lo largo de la vida en un amplio rango de edades (0-15 años). Las incursiones no mostraron una periodicidad notoria. Esta información debería integrarse a futuras acciones de manejo que deberían ser específicas para cada área considerando los patrones de migración que difieren entre los grandes ríos de la Cuenca.(AU)

A flowing atmospheric pressure afterglow as an ion source coupled to a differential mobility analyzer for volatile organic compound detection.

Atmospheric pressure glow discharges have been widely used in the last decade as ion sources in ambient mass spectrometry analyses. Here, an in-house flowing atmospheric pressure afterglow (FAPA) has been developed as an alternative ion source for differential mobility analysis (DMA). The discharge source parameters (inter-electrode distance, current and helium flow rate) determining the atmospheric plasma characteristics have been optimized in terms of DMA spectral simplicity with the highest achievable sensitivity while keeping an adequate plasma stability and so the FAPA working conditions finally selected were: 35 mA, 1 L min(-1) of He and an inter-electrode distance of 8 mm. Room temperature in the DMA proved to be adequate for the coupling and chemical analysis with the FAPA source. Positive and negative ions for different volatile organic compounds were tested and analysed by FAPA-DMA using a Faraday cup as a detector and proper operation in both modes was possible (without changes in FAPA operational parameters). The FAPA ionization source showed simpler ion mobility spectra with narrower peaks and a better, or similar, sensitivity than conventional UV-photoionization for DMA analysis in positive mode. Particularly, the negative mode proved to be a promising field of further research for the FAPA ion source coupled to ion mobility, clearly competitive with other more conventional plasmas such as corona discharge.

Effect of internal and external conditions on ionization processes in the FAPA ambient desorption/ionization source.

Ambient desorption/ionization (ADI) sources coupled to mass spectrometry (MS) offer outstanding analytical features: direct analysis of real samples without sample pretreatment, combined with the selectivity and sensitivity of MS. Since ADI sources typically work in the open atmosphere, ambient conditions can affect the desorption and ionization processes. Here, the effects of internal source parameters and ambient humidity on the ionization processes of the flowing atmospheric pressure afterglow (FAPA) source are investigated. The interaction of reagent ions with a range of analytes is studied in terms of sensitivity and based upon the processes that occur in the ionization reactions. The results show that internal parameters which lead to higher gas temperatures afforded higher sensitivities, although fragmentation is also affected. In the case of humidity, only extremely dry conditions led to higher sensitivities, while fragmentation remained unaffected.

Characterization of a new mobility separation tool: HRIMS as differential mobility analyzer.

High resolution ion mobility spectrometer (HRIMS) is a new instrument that uses parallel plate Differential Mobility Analysis as principle of separation. Gas phase analysis of volatile organic compounds (VOCs) has been performed for the characterization of this new mobility system using an UV-lamp for ionization. Studies of the effect of temperature and the presence of a desiccant are detailed. Identification of the different peaks obtained with an electrometer was successfully carried out for a group of alcohols, aromatic compounds and ketones (ethanol, 1-propanol, isopropanol, 1-butanol, 1-pentanol, 1-heptanol, acetone, 2-butanone, 2-pentanone, 2-octanone, benzene, toluene, xylene and bromobenzene) following a modified Millikan equation. Moreover, the investigation of the discrimination capabilities within the different VOCs families as well as the mobility dependence with molecular mass was successfully achieved.

Critical evaluation of the potential of radiofrequency pulsed glow discharge-time-of-flight mass spectrometry for depth-profile analysis of innovative materials.

The combination of radiofrequency pulsed glow discharge (RF-PGD) analytical plasmas with time-of-flight mass spectrometry (TOFMS) has promoted the applicability of this ion source to direct analysis of innovative materials. In this sense, this emerging technique enables multi-elemental depth profiling with high depth resolution and sensitivity, and simultaneous production of elemental, structural, and molecular information. The analytical potential and trends of this technique are critically presented, including comparison with other complementary and well-established techniques (e.g. SIMS, GD-OES, etc.). An overview of recent applications of RF-PGD-TOFMS is given, including analysis of nano-structured materials, coated-glasses, photovoltaic materials, and polymer coatings.

Thickness determination of subnanometer layers using laser ablation inductively coupled plasma mass spectrometry.

Laser ablation inductively coupled plasma mass spectrometry has been applied to determine the thickness of subnanometer (subnm) metallic layers. Metallic Nd was deposited onto Si wafers with 0.5, 1, 3, and 6 nm thickness and covered by a 10 nm Al coating. Integrated ion signals corresponded to the layer thickness, indicating that external calibration provides accurate data. Utilizing sensitivity ratios obtained from ablation of a glass standard reference material (SRM) and the Al layer as reference, the deviations between prepared and measured layer thickness were less than 10%. A further attempt was made to determine the layer thickness with the absolute sensitivity obtained from ablation of a glass SRM. The approach also yielded a linear correlation between determined and actual layer thickness, but bias and interday variability were significantly higher. This is assumed to result from imprecise determination of the crater size when ablating the glass SRM. This study shows that subnm layers of metals can be analyzed for their thickness either using reference materials of identical composition or using sensitivity ratios when one layer can be used as a reference. Absolute determination of the layer thickness is less accurate but can circumvent the lack of reference materials of similar composition.

Evaluation of pulsed radiofrequency glow discharge time-of-flight mass spectrometry for precious metal determination in lead fire assay buttons.

In this paper, an exploration of the capabilities and limitations of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (GD-TOFMS) for the determination of the precious metals Ag, Au, Pd, Pt and Rh in lead buttons obtained by Pb fire assay is reported on. Since the matrix consists almost entirely of lead (>99%), the occurrence of doubly charged Pb (Pb(2+)) ions can hinder accurate determination of Rh. This problem was counteracted by relying on the time-resolved formation of different ion types over the pulse period of the glow discharge, which allows discrimination against the Pb(2+) ions. The formation of ArCu(+) ions as a result of the use of a copper anode was assessed to pose no threat to the accuracy of the results obtained for the set of samples analyzed as its contribution to the total signal at m/z=103 could be adequately corrected for. The method developed was evaluated in terms of accuracy and precision using a set of Pb button standards with analyte concentrations between 5 and 100 µg g(-1). For the purpose of validation, a 10 µg g(-1) standard was considered as a sample. Overall, an acceptable accuracy was obtained with a bias of <5% between the experimental results and the corresponding reference values, except for Au, for which a larger deviation occurred. Precision values (repeatability) of typically <5% relative standard deviation (RSD) (for N=3) were obtained and the limits of detection (LODs) vary from ~0.020 µg g(-1) for Ag to ~0.080 µg g(-1) for Pt.

Pulsed radiofrequency glow discharge time-of-flight mass spectrometry for nanostructured materials characterization.

Progress in the development of advanced materials strongly depends on continued efforts to miniaturizing their structures; thus, a great variety of nanostructured materials are being developed nowadays. Metallic nanowires are among the most attractive nanometer-sized materials because of their unique properties that may lead to applications as interconnectors in nanoelectronic, magnetic, chemical or biological sensors, and biotechnological labels among others. A simple method to develop self-ordered arrays of metallic nanowires is based on the use of nanoporous anodic alumina (NAA) and self-assembled nanotubular titanium dioxide membranes as templates. The chemical characterization of nanostructured materials is a key aspect for the synthesis optimization and the quality control of the manufacturing process. In this work, the analytical potential of pulsed radiofrequency glow discharge with detection by time-of-flight mass spectrometry (pulsed rf-GD-TOFMS) is investigated for depth profile analysis of self-assembled metallic nanostructures. Two types of nanostructured materials were successfully studied: self-assembled NAA templates filled with arrays of single metallic nanowires of Ni as well as arrays of multilayered Au/FeNi/Au and Au/Ni nanowires and nanotubular titanium dioxide templates filled with Ni nanowires, proving that pulsed rf-GD-TOFMS allows for fast and reliable depth profile analysis as well as for the detection of contaminants introduced during the synthesis process. Moreover, ion signal ratios between elemental and molecular species (e.g., (27)Al(+)/(16)O(+) and (27)Al(+)/(32)O(2)(+)) were utilized to obtain valuable information about the filling process and the presence of possible leaks in the system.

Femtosecond laser ablation inductively coupled plasma mass spectrometry: fundamentals and capabilities for depth profiling analysis.

Laser ablation coupled to inductively coupled plasma mass spectrometry has become a versatile and powerful analytical method for direct solid analysis. The applicability has been demonstrated on a wide variety of samples, where major, minor, and trace element concentrations or isotope ratio determinations have been of interest. The pros and cons of UV-nsec laser ablation have been studied in detail, and indicate that aerosol generation, aerosol transport, and aerosol excitation-ionization within the ICP contribute to fractionation effects, which prevent this method from a more universal application to all matrices and all elements. Recent progresses in IR-fs and UV-fs laser ablation coupled to ICP-MS have been reported, which increase the inter-matrix and multi-element quantification capabilities of this method. These fundamental improvements in LA-ICP-MS are of significant importance for entering new applications in material science and related research fields. In particular, because coatings (conducting and non-conducting) consist of single or multilayers of various elemental composition and of different thickness (nm-mm range), significant progress in the field of depth profiling with fs-laser ablation can be expected. Therefore, in-depth profile analysis of polymers, semiconductors, and metal sample investigations, using ultra-fast laser ablation for sampling and the currently achievable figures of merit, are discussed. In this review manuscript, the enhanced capabilities of fs-LA-ICP-MS for direct solid sampling are highlighted, and it is discussed about current methods used for quantitative analysis and depth profiling, the ablation process of UV-ns and UV-fs, the influence of the laser beam profile, aerosol structure and transport efficiency, as well as the influence of the ICP-MS (e.g., vaporization and ionization efficiency in the plasma, and type of mass analyzer).

Laser ablation inductively coupled plasma mass spectrometry for direct analysis of the spatial distribution of trace elements in metallurgical-grade silicon.

The spatial distribution and concentration of impurities in metallurgical-grade silicon (MG-Si) samples (97-99% w/w Si) were investigated by use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The spatial resolution (120 mum) and low limits of detection (mg kg(-1)) for quality assurance of such materials were studied in detail. The volume-dependent precision and accuracy of non-matrix-matched calibration for quantification of minor elements, using NIST SRM 610 (silicate standard), indicates that LA-ICP-MS is well suited to rapid process control of such materials. Quantitative results from LA-ICP-MS were compared with previously reported literature data obtained by use of ICP-OES and rf-GD-OES. In particular, the distribution of element impurities and their relationship to their different segregation coefficients in silicon is demonstrated.

Depth profiling with modified dc-Grimm and rf-Grimm-type glow discharges operated with high gas flow rates and coupled to a high-resolution mass spectrometer.

The improved analytical capability of direct-current (dc) and radiofrequency (rf) "fast flow" glow discharges coupled to a sector field mass spectrometer (GD-SFMS) are presented. In particular, the effect of GD chamber design has been studied to obtain suitable crater shapes for depth-profile analysis of solid samples while maintaining the high sensitivity and stability of this source. In this study it was observed that the distance between the sample surface and the end of the flow tube is critical and so careful optimisation is needed. Under optimum conditions plane crater profiles, with high ion-signal sensitivity and sufficient stability, were obtained. The capability to determine qualitative and semi-quantitative depth profiles is presented here using, as model, a coated sample of certified thickness. Finally, the depth resolution achieved for qualitative depth profiles obtained by rf-GD-(SF)MS is compared with that for the well-established rf-GD optical emission spectroscopy (OES) technique.