Analytische Chemie
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Engineered nanomaterials (NM) with their large surface-to-volume ratios and their for some materials observed size-dependent functional properties are of increasing relevance for current and future developments in various fields such as medical and pharmaceutical industry, computing and electronics or food and consumer products. The performance and safety of NM are determined by the sum of their intrinsic physicochemical properties. Especially, the particle surface chemistry, which is largely controlled by the chemical nature and density of functional groups (FG) and ligands, is an important key driver for NM performance, stability, and processibility as well as the interaction of NM with the environment. Thus, methods for FG quantification can foster the sustainable development of functional and safe(r) NM.
Aiming at the development of simple, versatile, and multimodal tools for the quantification of many bioanalytically relevant FG and ligands, we investigated and compared various analytical methods commonly used for FG quantification. This includes electrochemical titration methods, dye-based optical assays, and other instrumental analytical techniques such as nuclear magnetic resonance and thermal analysis methods.
The potential of our multimodal approach for FG quantification was demonstrated for commercial and custom-made polymeric and silica particles of varying FG, used as optical pH sensors. In the future, our strategy can contribute to establish multi-method characterization strategies to provide a more detailed picture of the structure-properties relationship.
Process analytical technology (PAT) is a cross-sectional technology and thus essential for future smart production. While in the past decades, the focus of process optimization strategies was on increasing efficiency, in the future, the focus will be on the sustainability of a production and its products. In addition, products will be increasingly personalized in order to match the property profile exactly to the intended use. PAT is able to provide context-sensitive information at the molecular level for process control. Spectroscopic sensors can determine inline and simultaneously both the chemical composition and its sub-microscopic morphology. The article will focus on the optical spectroscopy and therefore starts with a brief introduction on the basic concepts of molecular spectroscopy. In addition, the particularities of measuring liquids, surfaces, or particulate systems in PAT applications are described. This should enable the reader to select the appropriate method for the specific problem. Many examples from everyday industrial practice illustrate the applications. The areas covered are the manufacturing industry, process and pharmaceutical industry, food industry, as well as biotechnology and medical technology. Future will show that PAT is especially important for applications in the field of medicine (point of care) circular economy (recycling, water–wastewater, etc.). It is important to emphasize that sustainability in industrial production can only be successful with an inter- and transdisciplinary close exchange between the different disciplines.
Lithium exists in two stable isotopes, 6Li and 7Li. The ratio of these in every ore varies depending on the geological history of the sample, thus providing a tool for fingerprinting the distinct origin of Li containing samples. Determination of the exact isotope ratio for e.g. designation of provenance today relies on expensive and bulky instrumentation such as multi `collector inductively coupled plasma mass spectrometry` (MC-ICP-MS). These instruments, however, are known to bear pitfalls in the characterization of particular elements including Lithium. BAM recently developed two alternative analytical devices for this task, solely relying on inexpensive optical spectroscopy in combination with state-of-the-art multivariate data analysis such as Machine learning algorithms. Both techniques have been comprehensively studied using certified reference materials and comparing the results to MC-ICP-MS results and could be shown to result in comparable figures of merit, paving the way for a more general accessibility to provenance determination instrumentation. The results also pave the way towards even further simplification of the laboratory infrastructure demands and to further include additional elements into the isotopic fingerprinting methodology.
Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products.
The Effect of Low Charge Polycarboxylate on C3A Passivation Monitored by Optical Spectroscopy
(2019)
Tricalcium aluminate (C3A) is less than 10 wt.% of the total cement composition; however, during hydration, the soluble C3A plays an important role in cement setting when mixed with the appropriate amount of sulfate.1 A good understanding about the balance of these components is therefore crucial to follow with the rapid growth of substitution materials and the rising levels of aluminate clinker. The aim of this investigation is the use of optical spectroscopy and in-situ X-ray diffraction utilizing a water-soluble organic dye (dye-S) to monitor early hydration of calcium aluminate (C3A) in the presence of 26 wt.% CaS04.2H2O (G) and PCE polymers with different charge densities (PCE-LC and PCE-HC). Phase characterization and optical evaluation were performed using in-situ X-ray diffraction and steady-state fluorescence and diffuse reflectance spectroscopy. Fluorescence spectroscopy of the reference C3A + dye-S revealed a fast decay in fluorescence intensity. However, in the presence of 26 wt.% G (C3A + dye-S + 26 wt.% G), a gradual increase in fluorescence intensity was observed in the first hours of reaction followed by a plateau that subsequently dropped in intensity after eight hours. The addition of PCE-LC and PCE HC to the mixture exhibited changes in the intensity threshold and overall a higher fluorescence intensity. Dye changes during hydration and structural changes will be further discussed.