Quantification anomalies in single pulse LA-ICP-MS analysis associated with laser fluence and beam size.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has undergone major improvements in recent years which have led to reduction of the analysis time, higher spatial resolution, and better sensitivity. However, quantification and accurate analysis remain one of the bottlenecks in LA-ICP-MS analysis and so far satisfactory calibration solutions are restricted to well-documented matrices and suitable internal standards. Additional uncertainties associated with laser fluence and beam size via various ablation cells and interfaces make quantification even more challenging. This work is focused on the influence of fluence, beam size and aerosol transport on quantification in single pulse LA-ICP-MS analysis via approaches based on pulse intensity, LA spot volumes, noise characteristics, etc. for different elements (As, Gd, La, Ni, Te and Zn), concentrations (between 10 and 1000 µg g-1), and matrices (gelatin standards and NIST SRM 612). The findings indicate that selection of the appropriate laser fluence, just above the ablation threshold, and beam size, depending on the interface of LA and ICP-MS, are critical for reliable quantification and should be properly adjusted to avoid excessive Poisson and Flicker noise, achieve maximum sensitivity, and prevent the formation of double peaks in single pulses.

Toward a Flexible and Efficient TiO2 Photocatalyst Immobilized on a Titanium Foil.

Titanium foils of different thicknesses were anodized, and the photocatalytic activity of the resulting TiO2 nanotube (NT) layers was determined. All of the titanium foils were anodized simultaneously under identical experimental conditions to avoid the influence of the aging of the anodizing electrolyte and other anodization parameters, such as voltage, time, and temperature. To characterize the microstructures of the titanium foils, we used electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and stylus profilometry analyses. The adhesion was tested with a Scotch tape test and the morphology of the TiO2 NTs was studied in detail using the SEM technique, while the surface areas of the TiO2 NTs were determined using a three-dimensional (3D) optical interference profilometer. With X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the chemical composition and structure of TiO2 oxide were established. The degradation of caffeine under UV irradiation was measured with a high-precision UV-vis-IR spectrophotometer, and the photoluminescence method was used to confirm the photocatalytic behavior of the TiO2 NT layers. The influence of the intrinsic properties, including twinning and the grain boundaries of the starting titanium foils with similar chemical compositions, was determined and explained. Finally, we identified the main characteristics that define a highly effective and flexible photocatalyst.

New Insights into Antibacterial and Antifungal Properties, Cytotoxicity and Aquatic Ecotoxicity of Flame Retardant PA6/DOPO-Derivative Nanocomposite Textile Fibers.

The aim of this study was to evaluate the antibacterial and antifungal activity, cytotoxicity, leaching, and ecotoxicity of novel flame retardant polyamide 6 (PA6) textile fibers developed by our research group. The textile fibers were produced by the incorporation of flame-retardant bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative (PHED) in the PA6 matrix during the in situ polymerization process at concentrations equal to 10 and 15 wt% (PA6/10PHED and PA6/15PHED, respectively). Whilst the nanodispersed PHED provided highly efficient flame retardancy, its biological activity led to excellent antibacterial activity against Escherichia coli and Staphylococcus aureus, as well as excellent antifungal activity against Aspergillus niger and Candida albicans. The results confirmed leaching of the PHED, but the tested leachates did not cause any measurable toxic effect to the duckweed Lemna minor. The in vitro cytotoxicity of the leached PHED from the PA6/15PHED sample was confirmed for human cells from adipose tissue in direct and prolonged contact. The targeted biological activity of the organophosphinate flame retardant could be beneficial for the development of PA6 textile materials with multifunctional properties and the low ecotoxicity profile, while the PHED's leaching and cytotoxicity limit their application involving the washing processes and direct contact with the skin.

Resolving the nanoparticles' structure-property relationships at the atomic level: a study of Pt-based electrocatalysts.

Achieving highly active and stable oxygen reduction reaction performance at low platinum-group-metal loadings remains one of the grand challenges in the proton-exchange membrane fuel cells community. Currently, state-of-the-art electrocatalysts are high-surface-area-carbon-supported nanoalloys of platinum with different transition metals (Cu, Ni, Fe, and Co). Despite years of focused research, the established structure-property relationships are not able to explain and predict the electrochemical performance and behavior of the real nanoparticulate systems. In the first part of this work, we reveal the complexity of commercially available platinum-based electrocatalysts and their electrochemical behavior. In the second part, we introduce a bottom-up approach where atomically resolved properties, structural changes, and strain analysis are recorded as well as analyzed on an individual nanoparticle before and after electrochemical conditions (e.g. high current density). Our methodology offers a new level of understanding of structure-stability relationships of practically viable nanoparticulate systems.

Electrochemical Dissolution of Iridium and Iridium Oxide Particles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry, and X-ray Absorption Spectroscopy Study.

Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.

Importance of non-intrinsic platinum dissolution in Pt/C composite fuel cell catalysts.

The dissolution of different platinum-based nanoparticles deposited on a commercial high-surface area carbon (HSAC) support in thin catalyst films is investigated using a highly sensitive electrochemical flow cell (EFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). The previously reported particle-size-dependent dissolution of Pt is confirmed on selected industrial samples with a mean Pt particle size ranging from 1 to 4.8 nm. This trend is significantly altered when a catalyst is diluted by the addition of HSAC. This indicates that the intrinsic dissolution properties are masked by local oversaturation phenomena, the so-called confinement effect. Furthermore, by replacing the standard HSAC support with a support having an order of magnitude higher specific surface area (a micro- and mesoporous nitrogen-doped high surface area carbon, HSANDC), Pt dissolution is reduced even further. This is due to the so-called non-intrinsic confinement and entrapment effects of the (large amount of) micropores and small mesopores doped with N atoms. The observed more effective Pt re-deposition is presumably induced by local Pt oversaturation and the presence of nitrogen nucleation sites. Overall, our study demonstrates the high importance and beneficial effects of porosity, loading and N doping of the carbon support on the Pt stability in the catalyst layer.

Metal maps of sclerotic hippocampi of patients with mesial temporal lobe epilepsy.

The loss of metal homeostasis has been implicated in the pathophysiology of mesial temporal lobe epilepsy associated with hippocampal sclerosis (mTLE-HS). Here we applied laser ablation inductively coupled plasma mass spectrometry imaging to establish the spatial distribution of Zn, Fe, Cu and Mn in coronal sections of hippocampi of four patients with drug-resistant mTLE-HS who underwent amygdalohippocampectomy. Detailed maps of the metal concentrations in the different morphological areas/layers were built and analyzed. The highest level of Zn (>20 µg g-1) was found in mossy fiber-rich regions - cornu ammonis field 4 (CA4), gyrus dentatus, and CA3. The distribution of Fe appears to reflect the routes of the main intrahippocampal blood vessels. The highest concentrations of Cu (>10 µg g-1) and Mn (>15 µg g-1) were observed in regions/layers with neuron somata - subiculum, CA4, gyrus dentatus, and stratum pyramidale (SPy) in CA1 and CA2. Alveus and other regions with axons and dendrites generally showed lower levels of Zn, Cu, and Mn. The Cu concentration was decreased in the areas of total neuronal loss in SPy in CA1 (9.73 ± 0.91 µg g-1), compared to the subiculum (13.32 ± 1.29 µg g-1; p = 0.043). The Cu and Mn concentrations correlated positively with neuron density in the SPy in CA1 (R = 0.629, p < 0.001; and R = 0.391, p = 0.004). These results provide a deeper insight into hippocampal metabolism of metals, and pave the road for identifying the components of the mechanism of epileptogenesis among Cu and Mn transporters and metalloproteins.

Novel Image Metrics for Retrieval of the Lateral Resolution in Line Scan-Based 2D LA-ICPMS Imaging via an Experimental-Modeling Approach.

The quality of elemental image maps obtained via line scan-based LA-ICPMS is a function of the temporal response of the entire system, governed by the design of the system and mapping and acquisition conditions used, next to the characteristics of the sample. To quantify image degradation, ablation targets with periodic gratings are required for the construction of a modulation transfer function (MTF) and subsequent determination of the lateral resolution as a function of image noise and contrast. Since such ablation targets, with suitable matrix composition, are not readily available, computer-generated periodic gratings were virtually ablated via a computational process based on a two-step discrete-time convolution procedure using empirical/experimental input data. This experimental-modeling procedure simulates LA-ICPMS imaging based on two consecutive processes, viz., LA sampling (via ablation crater profiles [ACP]) and aerosol washout/transfer/ICPMS measurement (via single pulse responses [SPR]). By random selection of experimental SPRs from a large database for each individual pulse during the simulation, the convolution procedure simulates an accurate elemental image map of the periodic gratings with realistic (proportional or flicker) noise. This facilitates indirect retrieval of the experimental lateral resolution for the matrix targeted without performing actual line scanning on periodic gratings.

The effect of fluoride ions on the corrosion behaviour of Ti metal, and Ti6-Al-7Nb and Ti-6Al-4V alloys in artificial saliva.

Metallic materials used for manufacture of dental implants have to exhibit high corrosion resistance in order to prevent metal release from a dental implant. Oral cavity is aggressive towards metals as it represents a multivariate environment with wide range of conditions including broad range of temperatures, pH, presence of bacteria and effect of abrasion. An increasing use of various Ti-based materials for dental implants and orthodontic brackets poses the question of their corrosion resistance in the presence of fluoride ions which are present in toothpaste and mouth rinse. Corrosion behaviour of Ti metal, Ti-6Al-7Nb and Ti-6Al-4V alloys and constituent metals investigated in artificial saliva is significantly affected by the presence of fluoride ions (added as NaF), as proven by electrochemical methods. Immersion test was performed for 32 days. During that time the metal dissolution was measured by inductively coupled plasma mass spectrometry. At the end of the test the composition, thickness and morphology of the surface layers formed were investigated by X-ray photoelectron spectroscopy and scanning electron microscopy.

The Effect of pH Value of a Simulated Physiological Solution on the Corrosion Resistance of Orthopaedic Alloys.

Metals and alloys used in orthopaedics and dentistry are exposed in vivo to various agents and environmental conditions. One of the important factors that determine the corrosion behaviour of metallic biomaterials is the pH of the environment. The corrosion resistance of stainless steel 316L (Fe/Cr18/Ni10/Mo3), titanium and titanium alloy Ti-6Al-4V (Ti90/Al6/V4) was studied in terms of their electrochemical properties and biodegradation in simulated physiological solutions of different pH values (4.5, 6.5, 7.5 and 8). The electrochemical characteristics of individual metal components were also investigated using cyclic voltammetry, linear polarization and potentiodynamic polarization methods. The concentration of dissolved metal ions released during 32 days immersion under simulated physiological conditions was determined by inductively coupled plasma mass spectroscopy. The corrosion behaviour of stainless steel 316L is strongly affected by the pH of the physiological solution in the range from 4.5 to 8.0. The corrosion resistance was enhanced at higher pH and the concentrations of released metal ions lower. The behaviour of titanium and its alloy however is almost independent of the pH.

Characterization of artificially generated PbS aerosols and their use within a respiratory bioaccessibility test.

A new method is presented for the preparation, characterization and use of PbS (galena) nanoparticles within an in vitro bioaccessibility test representing the respiratory tract, specifically the conditions occurring in conjunction with phagocytosis by cells using artificial lysosomal fluid. Particle production through nanosecond laser ablation enables their rapid production with a relatively narrow particle size distribution, and a diameter enabling them to represent particles that can enter the alveolar region of the respiratory tract (<3 microm). The PbS nanoparticles were characterized by cascade impaction to define their particle size distribution and through the use of X-ray diffraction (XRD) and electron microprobe analysis (EMPA) to define their mineralogy and homogeneity respectively. The particles were collected via liquid impingement in artificial lysosomal fluid and the undissolved material was separated via ultrafiltration after a contact time of 7-140 hours to define the bioaccessibility. The particles produced by the laser ablation of PbS have a homogenous composition and are 0.083-0.75 microm in diameter, spherical, crystalline, and have the same stoichiometry as the target material. Despite the low solubility constant of PbS in water (K(sp) = 3.4 x 10(-28)), 53% +/- 2.25 (SD) (n = 3) of the Pb was leached after ca. 48 hours, at which point equilibrium is reached. The competing effects of citrate and tartrate in the artificial lysosomal fluid are responsible for this high level of bioaccessibility. Nanoparticles of PbS display a level of bioaccessibility within human lungs that suggests they represent a significant risk to human health through the inhalation pathway as a result of phagocytosis, although this needs to be supported by in vivo tests.

Chromium in soil layers and plants on closed landfill site after landfill leachate application.

Landfill leachate (LL) usually contains low concentrations of heavy metals due to the anaerobic conditions in the methanogenic landfill body after degradation of easily degradable organic matter and the neutral pH of LL, which prevents mobilization and leaching of metals. Low average concentrations of metals were also confirmed in our extensive study on the rehabilitation of an old landfill site with vegetative landfill cover and LL recirculation after its treatment in constructed wetland. The only exception was chromium (Cr). Its concentrations in LL ranged between 0.10 and 2.75 mg/L, and were higher than the concentrations usually found in the literature. The objectives of the study were: (1) to understand why Cr is high in LL and (2) to understand the fate and transport of Cr in soil and vegetation of landfill cover due to known Cr toxicity to plants. The total concentration of Cr in LL, total and exchangeable concentrations of Cr in landfill soil cover and Cr content in the plant material were extensively monitored from May 2004 to September 2006. By obtained data on Cr concentration in different landfill constituents, supported with the data on the amount of loaded leachate, amount of precipitation and potential evapotranspiration (ETP) during the performance of the research, a detailed picture of time distribution and co-dependency of Cr is provided in this research. A highly positive correlation was found between concentrations of Cr and dissolved organic carbon (r=0.875) in LL, which indicates the co-transport of Cr and dissolved organic carbon through the system. Monitoring results showed that the substrate used in the experiment did not contribute to Cr accumulation in the landfill soil cover, resulting in percolation of a high proportion of Cr back into the waste layers and its circulation in the system. No negative effects on plant growth appeared during the monitoring period. Due to low uptake of Cr by plants (0.10-0.15 mg/kg in leaves and 0.05-0.07 mg/kg in stems of Salix purpurea), the estimated Cr offtake from LL by plants represented only a small proportion of the LL Cr mass load during the observation period, resulting in no dispersion of Cr into the environment through leaf drop.