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Eingeladener Vortrag
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Solvent-free sample preparation offers some advantages over solvent-based techniques, such as improved accuracy, reproducibility and sensitivity, for matrix-assisted laser desorption/ionization (MALDI) analysis. However, little or no information is available on the application of solvent-free techniques for the MALDI analysis of polymer blends. Solvent-free sample preparation by ball milling was applied with varying sample-to-matrix ratios for MALDI time-of-flight mass spectrometry analysis of various polymers, including polystyrenes, poly(methyl methacrylate)s and poly(ethylene glycol)s. The peak intensity ratios were compared with those obtained after using the conventional dried droplet sample preparation method. In addition, solvent-assisted milling was also applied to improve sample homogeneities.
Depending on the sample preparation method used, different peak intensity ratios were found, showing varying degrees of suppression of the signal intensities of higher mass polymers. Ball milling for up to 30 min was required to achieve constant intensity ratios indicating homogeneous mixtures. The use of wet-assisted grinding to improve the homogeneity of the blends was found to be disadvantageous as it caused partial degradation and mass-dependent segregation of the polymers in the vials.The results clearly show that solvent-free sample preparation must be carefully considered when applied to synthetic polymer blends, as it may cause additional problems with regard to homogeneity and stability of the blends.
Reliable measurement of the size of polydisperse, complex-shaped commercial nanopowders is a difficult but necessary task, e.g., for regulatory requirements and toxicity risk assessment. Suitable methods exist for the accurate characterization of the size of non-aggregated, stabilized, spherical and monodisperse nanoparticles. In contrast, industrial nanoscale powders usually require dedicated sample preparation procedures developed for the analysis method of choice. These nano-powders tend to agglomerate and/or aggregate, a behavior which in combination with an innate broad particle size distribution and irregular shape often significantly alters the achievable accuracy of the measured size parameters. The present study systematically tests two commercially available nanoscale powders using different sample preparation methods for correlative analysis by scanning electron microscopy, dynamic light scattering, Brunauer–Emmet–Teller method and differential mobility analysis. One focus was set on the sample preparation by embedding nanoparticles in carbon-based hot-mounting resin. Literature on this topic is scarce and the accuracy of the data extracted from cross sections of these particles is unclearly stated. In this paper systematic simulations on the deviation of the size parameters of well-defined series of nanoparticles with different shapes from the nominal value were carried out and the contributing factors are discussed.
Quantitative Microstructural Analysis - VAMAS TWA 37 & Liaison with ISO/TC 202 Microbeam Analysis
(2023)
The progress in activities on Microbeam Analysis under VAMAS/TWA 37 is reviewed. Particularly the liaison with the new projects within the ISO technical committee TC 202 is presented and discussed with respect to the identification and launching corresponding VAMAS projects. The ongoing project "FIB sample processing for TEM" is presented in detail.
The phenomenon of expelling nanomaterial from microparticles of different materials, such as Au, WO3 or B2O3 under the influence of a convergent electron beam (CB) of a transmission electron microscope (TEM) was reviewed by Ignacio Gonzalez-Martinez [1]. Converging the e-beam in a TEM means that a high amount of energy enters the microparticle at a very local place and interact with the matter. Obviously, during the convergent beam protocol, no imaging with the electron beam is possible, but at the end, nanoparticles with different appearances lie down next to the microparticle while its size is reduced.
Hence, there is a blind spot in the observation, which we want to fill, as we want to help clarify the nature of the expelling phenomenon. One hypothesis that explains the phenomenon is the so-called damage (of the microparticle) induced by an electric field (DIEF). Within this theory, the material is ionized and expelled in form of ionic waves. Our aim is therefore to fabricate specimens with artificial microlandscapes, as schematically exemplified in figure 1a), using the focused ion beam (FIB) and micromanipulators, as experimental setups to follow the paths of the expelled material.
As a first step towards the fabrication of such specimen, we make experimental feasibility studies for each fabrication method, FIB structuring with Ga+ ion beam and micromanipulated microparticle deposition. Bridges (gray regions in Fig. 1) are created by milling a commercially available electron transparent membrane (silicon oxide or carbon) of a Cu-TEM grid. Platinum or carbon walls (blue features in Fig. 1) are built to stand on those bridges. Microparticles (yellow sphere in Fig. 1) of gold or other material are deposited in the center of the bridges.
Figure 2a) shows four square holes (black area) and between them the residual silicon oxide membrane bridges (dark grey). On top of the bridges, walls (light grey) are deposited. The width of the bridges is different, the walls overlap the holes as well as the distance between the walls is very small, so these and other parameters need to be optimized. Figure 2b) shows a square hole (black) with bridges (white) on the right side on top of a carbon membrane (grey). There are still some obstacles which needs to be eliminated. For instance, the deposition process of the walls is not reliable as visible at the wall on top where a hole arises instead of a wall.
These studies are still in progress and the results are further discussed in terms of the applicability for the DIEF experiment in the TEM.
Nowadays, in every terrestrial and aquatic ecosystem, even in the remotest areas, small residues of plastics, the so called microplastic (MP) can be found. MPs are particles with a size of 1-1000 µm (ISO/TR 21960:2020), mainly containing synthetic polymers like polyethylene (PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate (PET). Even styrene-butadiene rubber (SBR) as an indication for tire wear is included due to similar particle formation. To understand the MPs consequences to the environment, it is of high priority to capture its extent of contamination. It is surprising that in the analysis of polymer masses in environmental samples, PE, PS and SBR are often detected, but only small amounts of PP, although this is the second most commonly produced standard plastic and many MP particles originate from carelessly disposed packaging materials.
This presentation provides hypotheses about the reasons of rare PP identification and mass quantification in environmental samples. Different investigations of pristine PP and representative environmental samples, including the pre-treatment by Accelerated Solvent Extraction (ASE) or with density separation followed by the thermal extraction / desorption gas chromatography-mass spectrometry (TED-GC/MS) are presented. The results are discussed according to the material properties and a possible degradation mechanism under different weathering conditions which indicate less stability under relevant storage conditions.
XPS of GR2M
(2022)
Experience gained at BAM within the European project ISGScope on the accurate measureemnt of graphene oxide flakes by electron microscopy is presented. Particularly, factors such as the type of solvent, substrate temperature, but also proper, gentle measurement parameters and image analysis conditions towards automation are highlighted. The measurement procedures in develeopment are being prepared to launch an inter-laboratory comparison under VAMAS (TWA41) as preparatory guidance for future standardisation at ISO.
Quantitative Microstructural Analysis - VAMAS TWA 37 & Liaison with ISO/TC 202 Microbeam Analysis
(2022)
The progress in activities on Microbeam Analysis under VAMAS/TWA 37 is reviewed. Particularly the liaison with the new projects within the ISO technical committee TC 202 is presented and discussed with respect to the possibility of identifying and launching related VAMAS projects. The recently started project FIB sample processing for TEM is highlighted. Need of more promotion for the engagement of more participants from industry and academia at national, European and international level is highlighted. Also, the competition with the other technical working areas (on 'nano' or materials-related) is critically discussed. Further, a short overview of the VAMAS areas of activities is given where Germany is involved. Planed regional VAMAS Workshops in Germany in 2023 are announced.
Whereas the characterization of nanomaterials using different analytical techniques is often highly automated and standardized, the sample preparation that precedes it causes a bottleneck in nanomaterial analysis as it is performed manually. Usually, this pretreatment depends on the skills and experience of the analysts. Furthermore, adequate reporting of the sample preparation is often missing. In this overview, some solutions for techniques widely used in nano-analytics to overcome this problem are discussed. Two examples of sample preparation optimization by au-tomation are presented, which demonstrate that this approach is leading to increased analytical confidence. Our first example is motivated by the need to exclude human bias and focuses on the development of automation in sample introduction. To this end, a robotic system has been de-veloped, which can prepare stable and homogeneous nanomaterial suspensions amenable to a variety of well-established analytical methods, such as dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), field-flow fractionation (FFF) or single-particle inductively coupled mass spectrometry (sp-ICP-MS). Our second example addresses biological samples, such as cells exposed to nanomaterials, which are still challenging for reliable analysis. An air–liquid interface has been developed for the exposure of biological samples to nanomaterial-containing aerosols. The system exposes transmission electron microscopy (TEM) grids under reproducible conditions, whilst also allowing characterization of aerosol composition with mass spectrometry. Such an approach enables correlative measurements combining biological with physicochemical analysis. These case studies demonstrate that standardization and automation of sample preparation setups, combined with appropriate measurement processes and data reduction are crucial steps towards more reliable and reproducible data.
Sample preparation for analytical scanning electron microscopy using initial notch sectioning
(2021)
A novel method for broad ion beam based sample sectioning using the concept of initial notches is presented. An adapted sample geometry is utilized in order to create terraces with a well-define d step in erosion depth from the surface. The method consists of milling a notch into the surface, followed by glancing-angle ion beam erosion, which leads to preferential erosion at the notch due to increased local surface elevation. The process of terrace formation can be utilized in sample preparation for analytical scanning electron microscopy in order to get efficient access to the depth-dependent microstructure of a material. It is demonstrated that the method can be applied to both conducting and non-conducting specimens. Furthermore, experimental parameters influencing the preparation success are determined. Finally, as a proof-of-concept, an electron backscatter diffraction study on a surface crystallized diopside glass ceramic is performed, where the method is used to analyze orientation dependent crystal growth phenomena occurring during growth of surface crystals into the bulk.