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Per- and polyfluoroalkyl substances (PFAS) are widely used for durable water-repellent finishing of different fabrics and textiles like outdoor clothing, carpets, medical textiles and more. Existing PFAS extraction techniques followed by target analysis are often insufficient in detecting widely used side-chain fluorinated polymers (SFPs) that are barely or non-extractable. SFPs are typically copolymers consisting of a non-fluorinated backbone with perfluoroalkyl side-chains to obtain desired properties. We compared the accessible analytical information and performance of complementary techniques based on oxidation (dTOP assay, PhotoTOP), hydrolysis (THP assay), standard extraction, extractable organic fluorine (EOF), and total fluorine (TF) with five functional textiles and characterized 7 further textiles only by PhotoTOP oxidation. The results show that when applied directly to textile samples, oxidation by dTOP and PhotoTOP and also hydrolysis by the THP are able to capture large fractions of the TF in form of perfluoroalkyl side-chains present in the textiles while methods relying on extracts (EOF, target and non-target analysis) were much lower (e.g., factor ~25-50 lower). The conversion of large fractions of the measured TF into PFCAs or FTOHs from fluorinated side chains is in contrast to previous studies. Concentrations ranged from <LOQ to over ~1000 mg F/kg after oxidation/hydrolysis and <LOQ to over 2000 mg F/kg for TF, while EOF and target PFAS in extracts were detected at much lower concentrations (up to ~ 60 mg F/kg) (amount of fluorine in the order: extraction << EOF << oxidation/hydrolysis ≤ TF). Perfluoroalkyl carboxylic acids (PFCAs) and fluorotelomer alcohols (FTOHs) from THP and PhotoTOP both represented the chain-length distribution in the textiles showing that long-chain SFPs are still used in current textiles. Further advantages and disadvantages of the applied methods are discussed.
Determination of elemental mass fractions in sediments plays a major role in evaluating the environmental status of aquatic ecosystems. Herewith, the optimization of a new total digestion protocol and the subsequent analysis of 48 elements in different sediment reference materials (NIST SRM 2702, GBW 07313, GBW 07311 and JMC-2) based on ICP-MS/MS detection is presented. The developed method applies microwave acid digestion and utilizes HBF4 as fluoride source for silicate decomposition. Similar to established protocols based on HF, HBF4 ensures the dissolution of the silicate matrix, as well as other refractory oxides. As HBF4 is not acutely toxic; no special precautions have to be made and digests can be directly measured via ICP-MS without specific sample inlet systems, evaporation steps or the addition of e.g. H3BO3, in order to mask excess HF. Different acid mixtures with and without HBF4 were evaluated in terms of digestion efficiency based on the trace metal recovery. The optimized protocol (5 mL HNO3, 2 mL HCL, 1 mL HBF4) allows a complete dissolution of the analyzed reference materials, as well as quantitative recoveries for a wide variety of certified analytes. Low recoveries for e.g. Sr, Ba and rare earth elements due to fluoride precipitation of HF-based digestions protocols, can be avoided by the usage of HBF4 instead. Based on the usage of high purity HBF4 all relevant trace, as well as matrix elements can be analyzed with sufficiently low LOQs (0.002 μg L−1 for U up to 6.7 μg L−1 for Al). In total, 34 elements were within a recovery range of 80%–120% for all three analyzed reference materials GBW 07313, GBW 07311 and JMC-2. 14 elements were outside a recovery range of 80%–120% for at least one of the analyzed reference materials.
Bacterial adhesion on surfaces of medical, water and food applications may lead to infections, water or food spoilage and human illness. In comparison to traditional static and macro flow chamber assays for biofilm formation studies, microfluidic chips allow in situ monitoring of biofilm formation under various flow regimes, have better environment control and smaller sample requirements.
In this work, a novel microfluidic platform is developed to investigate biofilm adhesion under precisely controlled bacteria concentration, temperature, and flow conditions. This platform central unit is a single-inlet microfluidic flow cell with a 5 mm wide chamber designed and tested to achieve ultra-homogenous flow in the central area of chamber. Within this area, defined microstructures are integrated that will disturb the homogeneity of the flow, thus changing bacterial adhesion pattern.
Here we present the monitoring of bacterial biofilm formation in a microfluidic chip equipped with a microstructure known as micro-trap. This feature is based on a 3D bacteria trap designed by Di Giacomo et al. and successfully used to sequester motile bacteria.
At first, fluorescent particles similar in size to Escherichia coli (E. coli) are used to simulate bacteria flow inside the flow cell and at the micro-trap. The turbulences induced by the trap are analyzed by imaging and particle tracking velocimetry (PTV). Secondly, the model strain E. coli TG1, ideal and well described for biofilm studies, is used to analyze biofilm formation in the micro-trap. Therefore, a stable fluorescent strain E. coli TG1-MRE-Tn7-141 is constructed by using Tn7 transposon mutagenesis according to the method described by Schlechter et al. Sequestering of E. coli cells within the micro-trap was followed using epifluorescence microscopy.
The novel microfluidic platform shows great potential for assessment of bacterial adhesion under various flow regimes. The performance of structural feature with respect to the generation of turbulences that promote or reduce bacterial adhesion can be systematically examined.
The combination of flow analysis and fluorescent strain injection into the microfluidic chip shows that the micro-trap is useful for capturing bacteria at defined positions and to study how flow conditions, especially micro-turbulences, can affect biofilm formation. It represents a powerful and versatile tool for studying the relation between topography and bacteria adhesion.
Homochirality is an obvious feature of life on Earth. On the other hand, extraterrestrial samples contain largely racemic compounds. The same is true for any common organic synthesis. Therefore, it has been a perplexing puzzle for decades how these racemates could have formed enantiomerically enriched fractions as a basis for the origin of homochiral life forms. Numerous hypotheses have been put forward as to how preferentially homochiral molecules could have formed and accumulated on Earth. In this article, it is shown that homochirality of the abiotic organic pool at the time of formation of the first self-replicating molecules is not necessary and not even probable. It is proposed to abandon the notion of a molecular ensemble and to focus on the level of individual molecules. Although the formation of the first self-replicating, most likely homochiral molecule, is a seemingly improbable event, on a closer look, it is almost inevitable that some homochiral molecules have formed simply on a statistical basis. In this case, the non-selective leap to homochirality would be one of the first steps in chemical evolution directly out of a racemic “ocean”. Moreover, most studies focus on the chirality of the primordial monomers with respect to an asymmetric carbon atom. However, any polymer with a minimal size that allows folding to a secondary structure would spontaneously lead to asymmetric higher structures (conformations). Most of the functions of these polymers would be influenced by this inherently asymmetric folding. Furthermore, a concept of physical compartmentalization based on rock nanopores in analogy to nanocavities of digital immunoassays is introduced to suggest that complex cell walls or membranes were also not required for the first steps of chemical evolution. To summarize, simple and universal mechanisms may have led to homochiral self-replicating systems in the context of chemical evolution. A homochiral monomer pool is deemed unnecessary and probably never existed on primordial Earth.
Homochirality is an obvious feature of life on Earth. On the other hand, extraterrestrial samples contain largely racemic compounds. The same is true for any common organic synthesis. Therefore, it has been a perplexing puzzle for decades how these racemates could have formed enantiomerically enriched fractions as a basis for the origin of homochiral life forms. Numerous hypotheses have been put forward as to how preferentially homochiral molecules could have formed and accumulated on Earth. In this article, it is shown that homochirality of the abiotic organic pool at the time of formation of the first self-replicating molecules is not necessary and not even probable. It is proposed to abandon the notion of a molecular ensemble and to focus on the level of individual molecules. Although the formation of the first self-replicating, most likely homochiral molecule is a seemingly improbable event, on a closer look, it is almost inevitable that homochiral molecules have formed simply on a statistical basis. In this case, the non-selective leap to homochirality would be one of the first steps in chemical evolution directly out of a racemic “ocean”. Moreover, most studies focus on the chirality of the primordial monomers with respect to an asymmetric carbon atom. However, any polymer with a minimal size that allows folding to a secondary structure, would spontaneously lead to asymmetric higher structures (conformations). Most of the functions of these polymers would be influenced by this inherently asymmetric folding. To summarize, simple and universal mechanisms may have led to homochiral self-replicating systems in the context of chemical evolution. A homochiral monomer pool is deemed unnecessary and probably never existed on primordial Earth.
The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.
Gallium – a versatile element for tuning the photoluminescence properties of InP quantum dots
(2019)
With the goal to tune the emission properties of colloidal InP quantum dots, the incorporation of Ga was explored. Unexpectedly, depending on the nature of the gallium precursor, the photoluminescence shifted either to the red (gallium oleate) or to the blue (gallium acetylacetonate). In the first case, larger-sized InP/GaP core/shell nanocrystals were formed, while in the second case the formation of an InGaP alloy structure enabled the blue range of emission (475 nm) to be accessed.
Fluorescent semiconductor nanocrystals, also known as quantum dots (QDs), enabled many advancements in biotechnology, photovoltaics, photocatalysis, quantum computing and display devices. The high versatility of this nanomaterial is based on their unique size-tunable photoluminescence properties, which can be adjusted from the visible to the near-infrared range. In contrast to other nanomaterials, QDs made the transition from a laboratory curiosity to the utilization in commercial products, like the QLED television screen or in smartphone displays. The best investigated QDs are composed of heavy metals like cadmium or lead, which is not the best choice in terms of toxicity and environmental pollution. A more promising material is Indium Phosphide (InP), which is also currently used by Samsung, Sony and co. in the QLED displays.
In this contribution, I would like to give you a sneak peek behind the curtains of nanomaterial synthesis and show how this material is produced, how to stabilize their structural properties, and assess their toxicity in environmentally relevant conditions. Furthermore, I would like to present a synthesis method to accomplish the last open challenge in display technology of a blue luminescent LED based on QDs by introducing a new element to the InP QDs.
The interaction of microplastics with freshwater biota and their interaction with other stressors is still not very well understood. Therefore, we investigated the ingestion, excretion and toxicity of microplastics in the freshwater gastropod Lymnaea stagnalis.
MP ingestion was analyzed as tissues levels in L. stagnalis after 6–96 h of exposure to 5–90 μm spherical polystyrene (PS) microplastics. To understand the excretion, tissue levels were determined after 24 h of exposure followed by a 12 h–7 d depuration period. To assess the toxicity, snails were exposed for 28 d to irregular PS microplastics (<63 μm, 6.4–100,000 particles mL−1), both alone and in combination with copper as additional stressor. To compare the toxicity of natural and synthetic particles, we also included diatomite particles. Microplastics ingestion and excretion significantly depended on the particle size and the exposure/depuration duration. An exposure to irregular PS had no effect on survival, reproduction, energy reserves and oxidative stress. However, we observed slight effects on immune cell phagocytosis. Exposure to microplastics did not exacerbate the reproductive toxicity of copper. In addition, there was no pronounced difference between the effects of microplastics and diatomite. The tolerance towards microplastics may originate from an adaptation of L. stagnalis to particle-rich environments or a general stress resilience. In conclusion, despite high uptake rates, PS fragments do not appear to be a relevant stressor for stress tolerant freshwater gastropods considering current environmental levels of microplastics.
Two nanosensors for simultaneous optical measurements of temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nm-sized silica-coated polystyrene nanoparticles (PS-NPs) doped with the near infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3 CrBPh4)[1][2] and an inert reference fluorescence dye (Nile Red NR or 5,10,15,20tetrakis-(pentafluorophenyl) porphyrin TFPP) and are covalently labeled with the pHsensitive fluorophore fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal distinguishable emission spectra suitable for ratiometric intensity-based and time-resolved studies in the visible and near infrared spectral region. The core-shell nanostructure of these sensors reveals high colloidal stability in various aqueous media. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of the TOP nanosensors for optically detecting the three bioanalytically and biologically relevant analytes temperature, oxygen and pH simultaneously at the same position.
Two nanosensors for simultaneous optical measurements of the bioanalytically and biologically relevant analytes temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nmsized silica-coated polystyrene nanoparticles (PS-NPs) doped with a near-infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3, CrBPh4) and an inert reference dye (Nile Red, NR or 5,10,15,20tetrakis(pentafluorophenyl) porphyrin, TFPP) and are covalently labeled with pHsensitive fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal spectrally distinguishable emission bands, allowing for ratiometric intensity-based and time-resolved studies in the visible and near-infrared wavelength region. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of these nanosensors for the sensitive luminescence readout of TOP simultaneously at the same spatialposition.
Two nanosensors for simultaneous optical measurements of temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nm-sized silica-coated polystyrene nanoparticles (PS-NPs) doped with the near infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3 CrBPh4)[1][2] and an inert reference fluorescence dye (Nile Red NR or 5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin TFPP) and are covalently labeled with the pH-sensitive fluorophore fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal distinguishable emission spectra suitable for ratiometric intensity-based and time-resolved studies in the visible and near infrared spectral region. The core-shell nanostructure of these sensors reveals high colloidal stability in various aqueous media. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of the TOP nanosensors for optically detecting the three bioanalytically and biologically relevant analytes temperature, oxygen and pH simultaneously at the same position.
Exploratory analysis of hyperspectral FTIR data obtained from environmental microplastics samples
(2020)
Hyperspectral imaging of environmental samples with infrared microscopes is one of the preferred methods to find and characterize microplastics. Particles can be quantified in terms of number, size and size distribution. Their shape can be studied and the substances can be identified. Interpretation of the collected spectra is a typical problem encountered during the analysis. The image datasets are large and contain spectra of countless particles of natural and synthetic origin. To supplement existing Analysis pipelines, exploratory multivariate data analysis was tested on two independent datasets. Dimensionality reduction with principal component analysis (PCA) and uniform manifold approximation and projection (UMAP) was used as a core concept. It allowed for improved visual accessibility of the data and created a chemical two-dimensional image of the sample. Spectra belonging to particles could be separated from blank spectra, reducing the amount of data significantly. Selected spectra were further studied, also applying PCA and UMAP. Groups of similar spectra were identified by cluster analysis using k-means, density based, and interactive manual clustering. Most clusters could be assigned to chemical species based on reference spectra. While the results support findings obtained with a ‘targeted analysis’ based on automated library search, exploratory analysis points the attention towards the group of unidientified spectra that remained and are otherwise easily overlooked.
Near-infrared (NIR) spectroscopy is a promising candidate for low-cost, nondestructive, and high-throughput mass quantification of micro¬plastics in environmental samples. Widespread application of the technique is currently hampered mainly by the low sensitivity of NIR spectroscopy compared to thermo-analytical approaches commonly used for this type of analysis. This study shows how the application of NIR spectroscopy for mass quantification of microplastics can be extended to smaller analyte levels by combining it with a simple and rapid microplastic enrichment protocol. For this purpose, the widely used flotation of microplastics in a NaCl solution, accelerated by centrifugation, was chosen which allowed to remove up to 99 % of the matrix at recovery rates of 83–104 %. The spectroscopic measurements took place directly on the stainless-steel filters used to collect the extracted particles to reduce sample handling to a minimum. Partial least squares regression (PLSR) models were used to identify and quantify the extracted microplastics in the mass range of 1–10 mg. The simple and fast extraction procedure was systematically optimized to meet the requirements for the quantification of microplastics from common PE-, PP-, and PS-based packaging materials with a particle size < 1 mm found in compost or soils with high natural organic matter content (> 10 % determined by loss on ignition). Microplastics could be detected in model samples at a mass fraction of 1 mg g-1. The detectable microplastic mass fraction is about an order of magnitude lower compared to previous studies using NIR spectroscopy without additional enrichment. To emphasize the cost-effectiveness of the method, it was implemented using some of the cheapest and most compact NIR spectrometers available.
Near-infrared (NIR) spectroscopy is a promising candidate for low-cost, nondestructive, and highthroughput mass quantification of microplastics in environmental samples. Widespread application of the technique is currently hampered mainly by the low sensitivity of NIR spectroscopy compared to thermoanalytical approaches commonly used for this type of analysis. This study shows how the application of NIR spectroscopy for mass quantification of microplastics can be extended to smaller analyte levels by combining it with a simple and rapid microplastic enrichment protocol. For this purpose, the widely used flotation of microplastics in a NaCl solution, accelerated by centrifugation, was chosen which allowed to remove up to 99 % of the matrix at recovery rates of 83–104 %. The spectroscopic measurements took place directly on the stainless-steel filters used to collect the extracted particles to reduce sample handling to a minimum. Partial least squares regression (PLSR) models were used to identify and quantify the extracted microplastics in the mass range of 1–10 mg.
The simple and fast extraction procedure was systematically optimized to meet the requirements for the quantification of microplastics from common PE-, PP-, and PS-based packaging materials with a particle size < 1 mm found in compost or soils with high natural organic matter content (> 10 % determined by loss on ignition). Microplastics could be detected in model samples at a mass fraction of 1 mg g-1. The detectable microplastic mass fraction is about an order of magnitude lower compared to previous studies using NIR spectroscopy without additional enrichment. To emphasize the cost-effectiveness of the method, it was implemented using some of the cheapest and most
compact NIR spectrometers available.
µ-FTIR spectroscopy is a widely used technique in microplastics research. It allows to simultaneously characterize the material of the small particles, fibers or fragments, and to specify their size distribution and shape. Modern detectors offer the possibility to perform two-dimensional imaging of the sample providing detailed information. However, datasets are often too large for manual evaluation calling for automated microplastic identification. Library search based on the comparison with known reference spectra has been proposed to solve this problem.
To supplement this ‘targeted analysis’, an exploratory approach was tested. Principal component analysis (PCA) was used to drastically reduce the size of the data set while maintaining the significant information. Groups of similar spectra in the prepared data set were identified with cluster analysis. Members of different clusters could be assigned to different polymer types whereas the variation observed within a cluster gives a hint on the chemical variability of microplastics of the same type. Spectra labeled according to the respective cluster can be used for supervised learning. The obtained classification was tested on an independent data set and results were compared to the spectral library search approach.
Working towards a comprehensive understanding of introduction pathways, number, and fate of micro¬plastics in the environment, suitable analytical methods are a precondition. Micro-spectroscopic methods are probably the most widely used techniques. Besides their ability to measure single spectra of a particle or fiber, most modern FTIR- and Raman microscopes are also capable of two-dimensional imaging. This is very appealing to microplastics research because it allows to simultaneously characterize the analytes chemically as well as their size (distribution) and shape.
Two-dimensional imaging on extensive sample areas with FTIR-micros¬copes is facilitated by focal plane array (FPA) detectors resulting in large data sets comprised of up to several million spectra. With numbers too large for manual inspection of each individual spectrum, automated data evaluation is inevitable. Identifying different polymers based on the comparison with known reference spectra (library search) has proven to be a suitable approach. For that purpose, FTIR-spectra of common plastics can be collected to create an individual reference library.
To Supplement this ‘targeted analysis’, looking for known substances via library search, an exploratory approach was tested. Principal component analysis (PCA) proved to be a helpful tool to drastically reduce the size of the data set while maintaining the significant information. Subsequently, cluster analysis was used to find groups of similar spectra. Spectra found in different clusters could be assigned to different polymer types. The variation observed within clusters gives a hint on chemical variability of microplastics of the same polymer found in the sample. Spectra labeled according to the respective cluster/polymer type were used to build a classification model which allowed to quickly predict the polymer type based on the FTIR spectrum. Classification was tested on a second, independent data set and results were compared to the spectral library search procedure.
Für die Erfassung der Verbreitung von Mikroplastik (MP) in der Umwelt ist die zeit- und kostenaufwendige Analysestrategie und der damit verbundene geringe Probendurchsatz eine limitierende Größe. Eine große Zahl verschiedener Studien dokumentriet das Auftreten von MP über den gesamten Globus. Meist sind die Studien aufgrund des großen analytischen Aufwands auf exemplarische, stichpunktartige Untersuchungen kleiner Umweltaliquoten und zahlenmäßig kleiner Probenumfänge begrenzt. Um die Verbreitung, die Eintragspfade und den Verbleib von MP in der Umwelt besser zu verstehen und effektive Vermeidungsstrategien abzuleiten, ist es jedoch notwendig, analytisch mehr Proben erfassen zu können.
Bildgebende mikro-spektroskopische Methoden wie das Raman- und FTIR-Imaging ermöglichen eine zeitaufwendige, umfassende Charakterisierung kleiner Umweltaliquoten. Neben der Partikelanzahl sind zusätzlich Informationen zu Partikelgröße, Größenverteilung und Oberflächenmorphologie zugänglich. Chemische und thermische Extraktionsverfahren sind bereits deutlich schneller und können diese Informationen durch eine Massenbilanz vervollständigen. Die analysierbare Probenmenge ist jedoch auf Milligramm Mengen beschränkt.
Wir schlagen daher vor, die Analyse von Proben auf MP durch ein vorangestelltes Screening mit der Nahinfrarot-Spektroskopie (NIRS) zur komplementieren. In diesem wird bereits eine erste Einschätzung über die Präsenz von MP in einer Probe gefällt und dadurch die wertvolle Messzeit anderer Methoden effizienter genutzt.
NIR zur Analyse von Polymeren wird seit langem eingesetzt, jedoch bisher lediglich im Rahmen einer Studie zur Mikroplastikuntersuchung mittels Hyperspektraler Bildgebung beschrieben. Der NIR Spektralbereich findet sich zwischen dem sichtbaren Licht und dem mittleren Infrarot (MIR). MIR Spektren sind durch klar definierte Banden charakterisiert, welche mehrheitlich von den Grundschwingungen der Moleküle stammen. Die höheren Energien im nahen Infrarot regen hingegen Kombinations- und Oberschwingungen der Streck und Biegeschwingungen an. Die resultierenden Absorptionsbanden sind oft breit und relativ unspezifisch. Erst mit Hilfe einer computergestützten Datenauswertung lassen sich aus diesen Spektren nützliche Informationen gewinnen. Dies erklärt die steigende Popularität der NIR-Spektroskopie in der jüngeren Vergangenheit mit einem Schwerpunkt als prozessanalytische Methode. NIR Spektrometer für das industrielle Prozessmonitoring zeichnen sich durch eine kompakte und robuste Konstruktionsweise aus. Die verfügbaren faseroptischen Reflexionssonden eignen sich gut um pulverförmige Proben zu untersuchen. Der räumlich erfassbare Messbereich kann durch die Sondengeometrie variiert werden. Sind die untersuchten Partikel im Verhältnis zur abgetasteten Fläche klein, wird als spektrale Information die Summe der Absorption aller Partikel im Sichtfeld erfasst. Die Methode ist deshalb nicht für Detailuntersuchungen von MP geeignet, erlaubt es jedoch innerhalb weniger Minuten eine Einschätzung über das Vorkommen von Mikroplastik in einer Probe zu treffen.
Exemplarisch wurden für diese Untersuchungen vier der am weitesten verbreiteten Kunststoffe Polyethylen (PE), Polyethylenterephthalat (PET), Polypropylen (PP) und Polystyrol (PS) gewählt. Aus den additivfreien Polymeren wurden nach einer Kryo-vermahlung und anschließender Siebung (< 125 µm) Modellproben generiert. Die Polymere wurden dafür zu einem Massenanteil von 1 % mit einem Standardboden (LUFA2.3, gesiebt < 125 µm) vermischt. Die Gesamtmenge von 1 g je Probe wurde in Aluminiumbehältern präpariert und 8 Messungen an unterschiedlichen, zufällig gewählten Positionen vorgenommen. Die erhaltenen Spektren wurden zur Kalibrierung chemometrischer Modelle genutzt.
In einem hierarchischen Ansatz wurde anhand der NIR-Spektren eine Klassifizierung vorgenommen:
1. Bestimmung ob eine Probe MP enthält (Ja/Nein).
2. Identifikation der Polymere in der Probe.
Eine aussagekräftige Klassifizierung beruht auf einer Vorbehandlung der Spektren. Hierdurch werden die Unterschiede zwischen den einzelnen Polymerbanden hervorgehoben. Die Eignung der so erstellten Modelle wurde anhand eines Referenzmaterials und am Beispiel von Realproben erfolgreich getestet. Dabei zeigte sich, dass nicht nur in den erstellten Polymer-Bodenmischungen, sondern auch in den Rückständen von fermentiertem Bioabfall und in Filterrückständen einer Waschmaschine, MP richtig erkannt wurde. Weiterhin zeigten Tests mit Mikroplastik-freien Bodenproben unterschiedlicher Herkunft, dass keine falsch-positive Resultate erzeugt wurden. Alle vier untersuchten Polymere, d.h. PE, PET, PS und PP mit einem Massenanteil von 1 % in einer Bodenmatrix werden auch bei einer gemischten Polymerzusammensetzung mit der NIR-Spektroskopie erkannt.
Der kombinierte Einsatz von NIRS und Chemometrie ermöglicht die Entscheidung über ein potenzielles Vorkommen sowie die Zuordnung des Materials der enthaltenen Polymerpartikel für eine Massefraktion ≥ 1 % in einer (trockenen) Probenmenge von 1 g innerhalb von 10–15 min. Der zeitaufwendige Schritt der Methode liegt hier in der Erstellung geeigneter chemometrischer Modelle sowie deren Validierung. Wesentliche Voraussetzung ist dabei, dass bei der Kalibrierung die Varianz der zu erwartenden Partikel und der Matrix realistisch abgebildet wird.
Fluorescent sensory MIP (molecularly imprinted polymer) particles were combined with a droplet-based 3D microfluidic system for the selective determination of a prototype small-molecule analyte of environmental concern, 2,4-dichlorophenoxyacetic acid or 2,4-D, at nanomolar concentration directly in water samples. A tailor-made fluorescent indicator cross-linker was thus designed that translates the binding event directly into an enhanced fluorescence signal. The phenoxazinone-type cross-linker was co-polymerized into a thin MIP layer grafted from the surface of silica microparticles following a RAFT (reversible addition-fragmentation chain transfer) polymerization protocol. While the indicator cross-linker outperformed its corresponding monomer twin, establishment of a phase-transfer protocol was essential to guarantee that the hydrogen bond-mediated signalling mechanism between the urea binding site on the indicator cross-linker and the carboxylate group of the analyte was still operative upon real sample analysis. The latter was achieved by integration of the fluorescent core-shell MIP sensor particles into a modular microfluidic platform that allows for an in-line phasetransfer assay, extracting the analyte from aqueous sample droplets into the organic phase that contains the sensor particles. Real-time fluorescence determination of 2,4-D down to 20 nM was realized with the system and applied for the analysis of various surface water samples collected from different parts of the world.
The plant secondary metabolite families of coumarin and 4-hydroxy coumarin have a broad pharmacological spectrum ranging from antibacterial to anticancer properties. One prominent member of this substance class is the synthetic but naturally inspired anticoagulant drug and rodenticide warfarin (coumadin). A vast number of publications focus on the identification of warfarin and its major cytochrome P450-mediated phase I metabolites by liquid chromatography (LC) with mass spectrometry (MS) and tandem mass spectrometric (MS/MS) detection techniques. For the first time, electron ionization (EI) induced high-resolution quadrupole time-of-flight mass spectrometric (HR-qToF-MS) data of in-liner derivatized warfarin and selected hydroxylated species is provided in this study as an alternative to LC-MS/MS approaches. Furthermore, the characteristic fragments and fragmentation pathways of the analyzed methyl ethers are concluded. The obtained data of analytical standards, specific deuterated and 13C-labeled compounds prove inductive cleavage of the acyl or acetonyl side chain, methyl migration, and H-migration, along with consequential inductive cleavage as predominant fragmentation routes. Based on the HR-spectral data, commonalities and differences between the analyzed compounds and fragment groups were evaluated with future applicability in structure elucidation and spectra prediction of related compounds.