Ursula E. A. Fittschen

Characteristics of Picoliter Droplet Dried Residues as Standards for Direct Analysis Techniques

The characteristics of dried residues of picodroplets of single-, two-, and three-element aqueous solutions, which qualify these as reference materials in the direct analysis of single particles, single cells, and other microscopic objects using, e.g., laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and micro-X-ray fluorescence (MXRF), were evaluated. Different single-, two-, and three-element solutions (0.01-1 g/L) were prepared in picoliter volume (around 130 pL) with a thermal inkjet printing technique. An achievable dosing precision of 4-15% was calculated by total reflection X-ray fluorescence (TXRF) determination of the transferred elemental mass of an array of 100 droplets. The size of the dried residues was determined by optical microscopy to be 5-20 microm in diameter depending on the concentration and the surface material. The elemental distribution of the dried residues was determined with synchrotron micro-X-ray fluorescence (SR-MXRF) analyses. The MXRF results show high uniformity for element deposition of every single droplet with an RSTD of 4-6% depending on the concentration of spotted solution. The shape and height profile of dried residues from picoliter droplets were studied using atomic force microscopy (AFM). It was found that these dry to give symmetrical spherical segments with maximum heights of 1.7 microm. The potential of this technique for direct LA-ICP-TOF-MS analysis is shown.

Confocal MXRF in environmental applications

In this review we highlight the performance of confocal micro X-ray fluorescence (CMXRF) for application in environmental science, citing contributions from recent studies (2008–2010). In CMXRF the use of focusing and collecting optics enables discrimination of the origin of fluorescence photons in three dimensions. It thereby enables simple and direct three dimensional imaging, and also the removal of unwanted signal contribution either from the depth of the sample or from its surface. By limiting the area of origin of fluorescence signal CMXRF can simplify quantitative approaches.

Side effects of a non‐peroxide‐based home bleaching agent on dental enamel

Changes in the chemistry and structure of enamel due to a non-peroxide-based home bleaching product (Rapid White) were studied in vitro using attenuated total reflectance-infrared spectroscopy, Raman spectroscopy, electron probe microanalysis, flame atomic absorption spectroscopy, and total reflection X-ray fluorescence. The results revealed that the citric-acid-containing gel-like component of the bleaching system substantially impacts on the dental hard tissue. Enamel is affected on several levels: (i) the organic component is removed from superficial and deeper enamel layers and remnants of the bleaching gel are embedded in the emptied voids; (ii) cracks and chemical inhomogeneities with respect to Ca and P occur on the surface; and (iii) within a submicron layer of enamel, the Ca-O bond strength in apatite decreases, thus enhancing calcium leakage from the bleached enamel hard tissue.

In Situ Functionalization and PEO Coating of Iron Oxide Nanocrystals Using Seeded Emulsion Polymerization

Herein we demonstrate that seeded emulsion polymerization is a powerful tool to produce multiply functionalized PEO coated iron oxide nanocrystals. Advantageously, by simple addition of functional surfactants, functional monomers, or functional polymerizable linkers-solely or in combinations thereof-during the seeded emulsion polymerization process, a broad range of in situ functionalized polymer-coated iron oxide nanocrystals were obtained. This was demonstrated by purposeful modulation of the zeta potential of encapsulated iron oxide nanocrystals and conjugation of a dyestuff. Successful functionalization was unequivocally proven by TXRF. Furthermore, the spatial position of the functional groups can be controlled by choosing the appropriate spacers. In conclusion, this methodology is highly amenable for combinatorial strategies and will spur rapid expedited synthesis and purposeful optimization of a broad scope of nanocrystals.

Shading in TXRF: calculations and experimental validation using a color X-ray camera

Absorption effects in total reflection X-ray fluorescence (TXRF) analysis are important to consider, especially if external calibration is to be applied. With a color X-ray camera (CXC), that enables spatially and energy resolved XRF analysis, the absorption of the primary beam was directly visualized for μL-droplets and an array of pL-droplets printed on a Si-wafer with drop-on-demand technology. As expected, deposits that are hit by the primary beam first shade subsequent droplets, leading to a diminished XRF signal. This shading effect was quantified with enhanced precision making use of sub-pixel analysis that improves the spatial resolution of the camera. The measured absorption was compared to simulated results using three different model calculations. It was found they match very well (average deviation < 10%). Thus errors in quantification due to absorption effects can be accounted for in a more accurate manner.

Evolution of anthropogenic aerosols in the coastal town of Salina Cruz, Mexico: part III size-segregated elemental composition analysed by total-reflection X-ray fluorescence spectrometry

Heavy metals in various size modes of the atmospheric aerosol are a concern for human health. Their and other elements’ concentrations are indicative for anthropogenic and natural aerosol sources. Si, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Hg, and Pb were determined as a complementary contribution to a study on aerosol cycling during the wet season, June 2004, in a humid, subtropical climate, i.e. in the city of Salina Cruz, situated on the Pacific coast of the Isthmus of Tehuantepec (16.2°N, 95.2°W), Mexico. For mass (gravimetry) and elemental analyses, particles were collected by a Berner low-pressure round nozzle cascade impactor using four stages corresponding to 0.1–0.25, 0.25–1.0, 1.0–4.0, and 4–16 µm of aerodynamic particle size. The impaction plates were modified such that approx. 1/6 consisted of a plastic support (Persplex®) for total reflection X-ray fluorescence spectrometry (TXRF). The elements’ total content was determined by TXRF without any further sample pretreatment. Limits of quantification (LOQ) for elemental content in individual impactor stages corresponded to 25–60 ng m−3 for Si; 0.8–4 ng m−3 for Cl, K, Ca, Ti, and V; 3–20 pg m−3 for Cr, Mn, Fe, Cu, Ni, and Zn; and 7–50 pg m−3 for As, Se, Br, Rb, Sr, Hg, and Pb. In some samples, however, high blank values for the supports gave an LOQ = 6–19 ng m−3 for Cl; 3--7 ng m−3 for Ca; 3–7 ng m−3 for Fe, Ni, Cu, and Zn; and 60–70 ng m−3 for Pb. The influence of local natural, industrial, and vehicle traffic sources for heavy-metal mobilization was obvious. Heavy-metal abundances did not coincide with regionally distributed pollutants. V and Ni were found at particularly elevated levels advected with the sea breeze, which points to ships as sources. Br and Pb were found at particularly low levels. The concentrations of Br, Rb, Sr, and Pb were found below LOQ at least in some, As, Co, Se, and Hg in all of the samples. The elements’ characteristic differences in mass size distributions were obvious despite the coarse size resolution. During the cycling of air masses from land to sea and back again, enrichment of super-micrometre particles in the near ground aerosol was observed under dry weather conditions. Rain preferentially removed the large particles with which heavy metals have been associated.

A setup for synchrotron-radiation-induced total reflection X-ray fluorescence and X-ray absorption near-edge structure recently commissioned at BESSY II BAMline.

An automatic sample changer chamber for total reflection X-ray fluorescence (TXRF) and X-ray absorption near-edge structure (XANES) analysis in TXRF geometry was successfully set up at the BAMline at BESSY II. TXRF and TXRF-XANES are valuable tools for elemental determination and speciation, especially where sample amounts are limited (<1 mg) and concentrations are low (ng ml(-1) to µg ml(-1)). TXRF requires a well defined geometry regarding the reflecting surface of a sample carrier and the synchrotron beam. The newly installed chamber allows for reliable sample positioning, remote sample changing and evacuation of the fluorescence beam path. The chamber was successfully used showing accurate determination of elemental amounts in the certified reference material NIST water 1640. Low limits of detection of less than 100 fg absolute (10 pg ml(-1)) for Ni were found. TXRF-XANES on different Re species was applied. An unknown species of Re was found to be Re in the +7 oxidation state.

Full-Field X-ray Fluorescence Microscopy Using a Color X-ray Camera

Introduction Elemental imaging of several elements simultaneously and with detection limits in the ppb range is achieved by synchrotron-based X-ray fluorescence microscopy, also often referred to as micro-X-ray fluorescence (MXRF). This has been shown, for example, by imaging Cu and U distribution in contaminated sediments [1] and P, Ca, and Zn distribution imaging of single cells and mitochondria [2]. A review on environmental application can be found in reference [3]. XRF micro-probes are available at synchrotrons all around the world and allow for 2D imaging with spatial resolution from several micrometers down to the nanometer range (30–100 nm); the latter mainly at thirdgeneration synchrotrons. X-ray fluorescence (XRF). Interaction of X-rays with matter is in general dominated by the absorption of photons to generate photoelectrons. Because of the relatively high energy of X-ray photons, core shell electrons are often targeted by this process. Relaxation of the core hole occurs by a transition of an outer shell electron and emission of the transition energy as either an Auger electron or a photon, usually in the X-ray energy range. The emitted fluorescent X-ray photon is characteristic of the excited element. This process is the basis for qualitative and quantitative determination of the elements present in the specimen, as well as XRF microscopy. As in other types of microscopy, MXRF can be performed in scanning mode or in full-field mode (Figure 1). Full-field MXRF. In the full-field MXRF mode, the full sample is illuminated by the X rays from the source, and the fluorescence is guided by an optic to the fluorescence array detector. This is illustrated in Figure 1a. Horizontal and vertical slit systems can be used to shape the beam. However, most MXRF setups operate in scanning mode, which means the sample is moved through a focused primary X-ray beam that excites the fluorescent X rays. A single element fluorescence detector can be used. This is illustrated in Figure 1b. The scanning mode comes with disadvantages regarding in situ applications where the sample must remain fairly static or where the sample is brittle or in other ways sensitive to movements. Here full-field MXRF is advantageous. An example is the imaging of elemental distributions in droplets (10–20 μL containing Mn, Ni, Cu, and Sc) while drying. This is shown in Figure 2. The droplets were allowed to dry undisturbed while the elemental information was recorded. Full-field MXRF allows for fast imaging of large areas (for example, 12×12 mm2 at 1,000 frames per second and 264×264 pixels) and therefore simultaneous detection of elemental changes over the entire field of view, which can be important for certain in situ applications. However, the detectability of each element will depend on the fluorescence yield of the element and the total counts acquired. Thus, the recording frequency will be limited by the need to acquire enough counts for detecting specific elements. Full-field MXRF also allows fast 3D elemental imaging by taking images at different depths of the sample using a sheet beam.

2D and 3D Imaging of Li-Ion Battery Materials Using Synchrotron Radiation Sources

Characterization of microstructural properties in electrodes for Li-Ion batteries can be regarded a key factor to understand functionality and aging process in the cells. X-ray microscopy has proven extremely powerful to capture a number of morphological parameters such as porosity, tortuosity or particle size distribution but also chemical information regarding phase distribution, state of charge or elemental migration over a large range of length scales. With their high penetration power utilizing various contrast methods X-rays offer deep insight into the battery materials and microstructural characteristics.