Vid Simon Šelih

New Insight into Platinum Dissolution from Nanoparticulate Platinum‐Based Electrocatalysts Using Highly Sensitive In Situ Concentration Measurements

Time‐ and potential‐resolved electrochemical Pt dissolution from commercial Pt and prepared PtCu alloy nanoparticulate catalysts have been studied under potentiodynamic conditions in 0.1 M HClO4 by using on‐line inductively coupled plasma mass spectrometry (ICP‐MS). For the first time the exact amount of dissolved Pt per cycle has been measured on real electrocatalysts. Results show clearly that Pt dissolution depends on the particle size: approximately seven times as much Pt is released into the solution from commercial 3 nm Pt particles as from a commercial 30 nm Pt sample. The stability of our prepared PtCu electrocatalyst is higher than that of a commercial 3 nm electrocatalyst, which is, however, still slightly lower than that of a commercial 30 nm Pt electrocatalyst.

Comparison of laser ablation-inductively coupled plasma-mass spectrometry and micro-X-ray fluorescence spectrometry for elemental imaging in Daphnia magna

Visualization of elemental distributions in thin sections of biological tissue is gaining importance in many disciplines of biological and medical research. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and scanning micro-X-ray fluorescence spectrometry (micro-XRF) are two widely used microanalytical techniques for elemental mapping. This article compares the capabilities of the two techniques for imaging the distribution of selected elements in the model organism Daphnia magna in terms of detection power and spatial resolution. Sections with a thickness of 10 and 20 microm of the fresh water crustacean Daphnia magna were subjected to LA-ICP-MS and micro-XRF analysis. The elemental distributions obtained for Ca, P, S and Zn allow element-to-tissue correlation. LA-ICP-MS and micro-XRF offer similar limits of detection for the elements Ca and P and thus, allow a cross-validation of the imaging results. LA-ICP-MS was particularly sensitive for determining Zn (LOD 20 microg g(-1), 15 microm spot size) in Daphnia magna, while the detection power of micro-XRF was insufficient in this context. However, LA-ICP-MS was inadequate for the measurement of the S distributions, which could be better visualized with micro-XRF (LOD 160 microg g(-1), 5 s live time). Both techniques are thus complementary in providing an exhaustive chemical profiling of tissue samples.

Multi-element analysis of wines by ICP-MS and ICP-OES and their classification according to geographical origin in Slovenia

Inductively coupled plasma mass spectrometry and optical emission were used to determine the multi-element composition of 272 bottled Slovenian wines. To achieve geographical classification of the wines by their elemental composition, principal component analysis (PCA) and counter-propagation artificial neural networks (CPANN) have been used. From 49 elements measured, 19 were used to build the final classification models. CPANN was used for the final predictions because of its superior results. The best model gave 82% correct predictions for external set of the white wine samples. Taking into account the small size of whole Slovenian wine growing regions, we consider the classification results were very good. For the red wines, which were mostly represented from one region, even-sub region classification was possible with great precision. From the level maps of the CPANN model, some of the most important elements for classification were identified.

Multi-element quantification of ancient/historic glasses by laser ablation inductively coupled plasma mass spectrometry using sum normalization calibration.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for quantitative analysis of ancient/historic glasses is subject to calibration issues which have been addressed in this work. Since ancient/historic glasses have widely ranging matrix compositions, a complementary analysis by an alternative method is generally employed to determine at least one major element which can be used as an internal standard. We demonstrate that such a complementary analysis is unnecessary using a so-called sum normalization calibration technique (mathematically formulated) by simultaneous measurement of 54 elements and normalizing them to 100% [w/w] based on their corresponding oxide concentrations. The crux of this approach is that by assuming a random internal standard concentration of a particular major oxide, e.g. SiO2, the normalization algorithm varies the internal standard concentration until the cumulated concentrations of all 54 elemental oxides reach 100% [w/w]. The fact that 54 elements are measured simultaneously predetermines the laser ablation mode to rastering. Nine glass standards, some replicating historic compositions, were used for calibration. The linearity of the calibration graphs (forced through the origin) represented by the relative standard deviations in the slope were between 0.1 and 6.6% using SiO2 as an internal standard. This allows high-accuracy determination of elemental oxides as confirmed by good agreement between found and reported values for major and minor elemental oxides in some synthetic glasses with typical medieval composition (European Science Foundation 151 and 158). Also for trace elemental concentrations of lanthanides in a reference glass (P&H Developments Ltd. DLH7, a base glass composition with nominally 75 microg g(-1) elements added) accurate data were obtained. Interferences from polyatomic species and doubly charged species on the masses of trace elements are possible, depending on the base composition of the glass, with Ba and Sb glasses showing potential interferences on some lanthanides. We showed that they may be reduced to a great extent by using an Octopole Reaction System although the overall sensitivity decreases which may be a problem for some low-level determinations.

3D laser ablation-ICP-mass spectrometry mapping for the study of surface layer phenomena – a case study for weathered glass

In this work, a multi-elemental 3D laser ablation-ICP-mass spectrometry mapping procedure for high-resolution depth information retrieval to investigate surface layer phenomena is presented. The procedure is based on laser drilling on a virtual grid on the surface, followed by extraction of depth maps along the z-axis (for each element monitored). Using a burst of 50 laser pulses at 1 Hz on each point of the grid, a penetration rate of ca. 150 nm per pulse (in glass) was obtained and a lateral resolution in the order of the laser beam diameter. By ultrafast ICP-MS monitoring of individual ablation pulses (58 ms for a set of 19 elements) using a laser ablation cell with fast signal washout (less than 0.5 s for whole laser pulse), the corresponding peak areas could be consistently integrated, resulting in spatial elemental data associated with individual pulses. The usual laser drilling limitations such as pulse mixing and signal tailing are avoided with this approach. After manipulation of the spatial elemental datasets and quantification, stacks of 50 2D depth maps (for each element monitored) were produced which could be visualized as volume images or time-lapse movies. As a proof of concept, this approach was successfully used to investigate the degradation mechanisms of a medieval, weathered glass artifact by colocalization analysis of selected cross-sectional 2D elemental images in arbitrary planes of the volume images. It was shown that degradation must have started as a result of dealkalinization leading to depletion of alkalis/earth alkalis in glass surface layers and enrichment of network formers (Si and Al), and subsequent worsening by cracking and formation of corrosion pits and so-called spatiotemporal Liesegang rings indicative of radial leaching.

Basic modeling approach to optimize elemental imaging by laser ablation ICPMS.

The quality of element image maps generated by laser ablation (LA) ICPMS rastering depends on the measurement conditions (laser fluence, repetition rate, beam diameter, scanning speed, flow rate, and acquisition time). Optimizing these conditions is often a matter of trial and error since the quality criteria for elemental imaging (sensitivity, spatial resolution, noise, and analysis time) are intricately linked. A simple mathematical model, and ensuing software, was developed to simulate the LA-ICPMS output upon virtual rastering of a digital image of a cross-section of a sample. Even though the LA-ICPMS map is not directly correlated with elemental imaging, element distributions are often related to visual features in the sample, allowing optimization of the LA-ICPMS settings for the desired quality criteria (samples without any visual features can not be optimized in this way). The virtual LA-ICPMS rastering software assumes that the ablation cell and tube interface act as a continuous stirred-tank reactor (i.e., exponential washout) and a plug flow reactor (i.e., zero dispersion), respectively, using an inert gas for transport of the aerosol particles. The software also incorporates a random noise generator which simulates the experimentally deduced signal-to-noise ratios as a function of the anticipated concentration and LA-ICPMS settings. The software was successfully validated and demonstrated by comparing the software output of selected patterns created in the emulsion of a black-and-white negative film with the experimental rastering output performed by measurement of (107)Ag in the emulsion.

Quantitative multi-element mapping of ancient glass using a simple and robust LA-ICP-MS rastering procedure in combination with image analysis.

AbstractThe surface of two glass artefacts in mosaic style, probably fragments of conglomerate glass bowls dating back two millennia, was investigated by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). By rastering with the laser beam over a selected area of the surface of the glass artefacts, elemental oxide maps were generated. Quantification of the elemental oxides in the maps was achieved using a so-called sum normalization procedure, summating the elements—54 in total—as their oxides to 100% (w/w), without using an internal standard and applying only one external standard (NIST SRM glass 610). This results in a robust mapping procedure which automatically corrects for drift and defocusing issues. Sum normalization was applied to each pixel in the map separately and required a custom source code to process all the data in the tens of thousands of pixels to generate the elemental oxide concentration maps. The digital element maps generated upon rastering of the two glass artefacts are very compelling and are an excellent entry point to gain detailed insight into their fabrication and provenance using image analysis software for retrieval of localized elemental oxide concentrations and correlations. FigureInvestigated decorative glass artefact, probably a fragment of a glass bowl dating back two millenia

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.

Evaluation of a method for treatment of iron gall ink corrosion on paper

AbstractIron gall ink was the most widely used writing ink for paper from the Middle Ages to the twentieth century. Unfortunately, the ink ingredients contain corrosive transition metal ions and acids that cause severe damage to the paper carrier. New or improved paper conservation methods for iron gall ink stabilization are constantly sought. The aim of the study was evaluation of a recently proposed stabilization treatment, adapted to lower relative humidity, applied to various model and historical paper samples containing iron gall ink. The effect of stabilization treatment on paper samples during artificial thermal aging was followed by the determination of the molecular weight distribution by size exclusion chromatography and colorimetry. Migration of iron and copper compounds from the ink lines was monitored by laser ablation inductively coupled plasma mass spectrometry. The results demonstrate that effective stabilization of iron gall ink-containing paper can be successfully achieved by interleaving with papers impregnated with the antioxidant tetrabutylammonium bromide and alkaline buffer under experimental conditions. Negative side effects of the stabilization treatment, such as migration of iron or copper ions from the ink lines and changes of color after the treatment and after accelerated thermal degradation, were limited, proving that the proposed stabilization treatment can be considered for future use by conservators.

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.