Analytische Chemie
Filtern
Erscheinungsjahr
Dokumenttyp
- Vortrag (2194)
- Zeitschriftenartikel (1943)
- Posterpräsentation (1009)
- Beitrag zu einem Tagungsband (514)
- Sonstiges (128)
- Forschungsbericht (65)
- Forschungsdatensatz (57)
- Buchkapitel (52)
- Dissertation (39)
- Newsletter (38)
Sprache
- Englisch (5002)
- Deutsch (1052)
- Mehrsprachig (54)
- Spanisch (5)
- Russisch (4)
- Französisch (3)
- Polnisch (2)
- Italienisch (1)
Schlagworte
- Fluorescence (236)
- Nanoparticles (194)
- LIBS (143)
- Concrete (136)
- XPS (121)
- Quantum yield (117)
- Nanoparticle (112)
- Mechanochemistry (101)
- Zerstörungsfreie Prüfung (101)
- Ultrasound (98)
Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (1471)
- 8 Zerstörungsfreie Prüfung (1320)
- 6 Materialchemie (1065)
- 6.1 Oberflächen- und Dünnschichtanalyse (368)
- 6.3 Strukturanalytik (337)
- 8.0 Abteilungsleitung und andere (330)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (328)
- 1.1 Anorganische Spurenanalytik (290)
- 1.2 Biophotonik (269)
- 8.4 Akustische und elektromagnetische Verfahren (259)
Paper des Monats
- ja (27)
Der Beitrag beschreibt den Aufbau und die Entwicklung einer Heißluftquelle als Wärmequelle für die aktive Thermografie. Als Ausgangspunkt wird zunächst die Quellenlage betrachtet. In der Literatur über Thermografie spielt Heißluft als Wärmequelle nur in weniger als 0,1% eine Rolle, die Ursache dafür ist nicht bekannt. Es wird vermutet, dass dieser Erwärmungsmethode unterstellt wird, sie hätte Nachteile bezüglich Homogenität der Erwärmung sowie Leistungseintrag. In einer der raren Publikationen über einen Verfahrensvergleich schnitt die Heißluft-Thermografie jedoch nicht schlechter als die Vergleichsverfahren mit optischer Anregung ab, bei gleichzeitig deutlichem Zeitgewinn und geringerem technischen Aufwand.
Danach wird der fertige Versuchsaufbau mit seinen wesentlichen Komponenten dargestellt. Der Einfluss der Geometrie der Luftaustrittsdüse auf die erreichbare Wärmeverteilung an einem flachen Blech wurde an mehreren Düsen untersucht. Hierbei erwies sich eine langgestreckte Umlenkdüse mit einer Strahlumlenkung von etwa 20° als optimal zur Erzeugung einer möglichst homogenen Erwärmung.
Ein weiterer zu optimierender Parameter war die erreichbare Schaltdynamik des Heißgasstromes. Beim schnellen Schalten großer Volumenströme treten Druckstöße mit entsprechenden Temperaturänderungen auf. Hinzu kommt, dass der verwendete MFC (mass flow controller) bei großen Volumenströmen zum Einschwingen bei Schaltprozessen neigt.
Daher enthält der Aufbau einen offenen Bypass zur Stabilisierung des Volumenstroms. Mit dem so realisierten Messplatz wurde die Reproduzierbarkeit der erzielten Erwärmung durch mehrfache Wiederholungsmessungen über einen längeren Zeitraum untersucht. Hierzu wurde ein auch zu Validierungszwecken genutzter PVC-Block mit 13 mm Dicke jeweils für 60 s erwärmt und die Oberflächentemperatur des PVC-Blocks mit einer IR-Kamera aufgezeichnet. Bei jeweiligem Neuaufbau ohne Justierhilfe ergab sich eine Reproduzierbarkeit von etwa 22% bei 5 Versuchen. Unter Nutzung einer Justierhilfe (Schablone für Abstand in der Kamerasoftware) ließ sich die Reproduzierbarkeit auf 5% bei 7 Versuchen reduzieren.
Ein weiterer zu klärender Punkt war der erzielbare Wärmeeintrag im Vergleich zu einer Anregung mit Blitzlampen. Hierzu wurde eine Messung mit 60 s Heißluftheizung direkt mit einer Evaluierungsmessung mit Blitzlampen am gleichen PVC-Probekörper mit 4 FBB an der Rückseite verglichen. Die Inhomogenität der Erwärmung wurde durch eine Phasenauswertung unterdrückt. Die Phasenauswertung gestattete den Nachweis aller 4 FBB, wobei das Signal zu Rausch-Verhältnis bei der Heißlufterwärmung deutlich besser war. Der direkte Vergleich der Temperaturkurven zeigt, dass bei 60 s Heizlufterwärmung ca. 4,5 mal mehr Energie als bei der Blitzanregung vom Probekörper absorbiert wurde. Hieraus lässt sich die eingekoppelte Heizleistung mit 100 mW/cm² abschätzen. Das entspricht in etwa dem Niveau, wie es auch mit bewegten Halogenstrahlern, bewegten IR-Strahlern oder der Sonne erreicht wird.
Diese Ergebnisse belegen, dass eventuell vorhandene Vorbehalte gegenüber einer Heißluft als Wärmequelle für die aktive Thermografie zumindest für thermisch langsame Materialien wie Kunststoffe oder mineralische Baustoffe unbegründet sind. Die Einsatzgrenzen bei der Untersuchung thermisch schnellerer Materialien wie Metalle steht noch aus, hier ist mit Abstrichen zu rechnen. Auf der anderen Seite lässt eine mögliche Düsenoptimierung noch deutliche Verbesserungen erwarten.
Pulsed thermography is a well-known non-destructive testing technique and has proven to be a valuable tool for examination of material defects, to determine thermal material parameters, and the thickness of test specimens through calibration or mathematical models. However, the application to semitransparent materials is quite new and demanding, especially for semitransparent materials like epoxy, polyamide 12, or glass fiber reinforced polymers with epoxy or polyamide matrix.
In order to describe the temporal temperature evolution in such materials, which are recorded with an infrared camera during pulse thermography experiments, much more influences have to be considered, compared to opaque materials:
- The wavelength of the excitation source and the spectral range of the infrared camera
- The angles between the specimen, the excitation source and the infrared camera
- The area behind the specimen
- The roughness of the material surface
- The scattering mechanism within the material
Here, we will consider all these influences and describe how they can be treated mathematically in analytical or numerical models (using COMSOL Multiphysics software). These models describe the temperature development during the pulse thermography experiment in reflection and transmission configuration. By fitting the results of the mathematical models to experimental data it is possible to determine the thickness or the optical and thermal properties of the specimen.
Matrix‐assisted ionization (MAI) mass spectrometry does not require voltages, a laser beam, or added heat to initiate ionization, but it is strongly dependent on the choice of matrix and the vacuum conditions. High charge state distributions of nonvolatile analyte ions produced by MAI suggest that the ionization mechanism may be similar to that of electrospray ionization (ESI), but different from matrix‐assisted laser desorption/ionization (MALDI). While significant information is available for MAI using mass spectrometers operating at atmospheric and intermediate pressure, little is known about the mechanism at high vacuum.
Eleven MAI matrices were studied on a high‐vacuum time‐of‐flight (TOF) mass spectrometer using a 266 nm pulsed laser beam under otherwise typical MALDI conditions. Detailed comparisons with the commonly used MALDI matrices and theoretical prediction were made for 3‐nitrobenzonitrile (3‐NBN), which is the only MAI matrix that works well in high vacuum when irradiated with a laser.
Screening of MAI matrices with good absorption at 266 nm but with various degrees of volatility and laser energies suggests that volatility and absorption at the laser wavelength may be necessary, but not sufficient, criteria to explain the formation of multiply charged analyte ions. 3‐NBN produces intact, highly charged ions of nonvolatile analytes in high‐vacuum TOF with the use of a laser, demonstrating that ESI‐like ions can be produced in high vacuum. Theoretical calculations and mass spectra suggest that thermally induced proton transfer, which is the major ionization mechanism in MALDI, is not important with the 3‐NBN matrix at 266 nm laser wavelength. 3‐NBN:analyte crystal morphology is, however, important in ion generation in high vacuum.
The 3‐NBN MAI matrix produces intact, highly charged ions of nonvolatile compounds in high‐vacuum TOF mass spectrometers with the aid of ablation and/or heating by laser irradiation, and shows a different ionization mechanism from that of typical MALDI matrices.
The reliable identification and quantification of phosphorylated amino acids, peptides and proteins is one of the key challenges in contemporary bioanalytical research, noteworthy, to diagnose and treat diseases at an early developmental stage1. Miniaturised sensing devices like microfluidic chips combined with “smart” detection chemistry, simple data assessment, processing and presentation are very attractive for benchtop use in clinical environments.
We developed novel synthetic probes targeting phosphorylated amino acids, based on core-shell microparticles consisting of a silica core coated with a molecularly imprinted polymer (MIP) shell. These “plastic antibodies” are extremely robust, resist denaturing solvents and elevated temperatures, can be reproducibly produced at low cost, and potentially overcome many of the practical problems in current bioanalytical detection strategies. The MIP layer contains a fluorescent probe monomer, binds selectively to phosphorylated tyrosine (pY) with a significant imprinting factor higher than 3.5 and responds with a “lighting-up” of its fluorescence accompanied by the development of a strongly red-shifted emission band toward the analyte. In analogy to our previous work4, the bead-based ratiometric detection scheme has also been successfully transferred to a microfluidic chip format to demonstrate its applicability to rapid assays. Such a miniaturised device could yield an automated pY measurement system in the future. The setup was built by coupling a modular microfluidic system5 for amino acid functionalisation (Fmoc protection) and, as shown in Figure 1, a multi-layer PDMS/Teflon/glass microfluidic chip6 for buffering, extraction (micropillars co-flow extraction) and selective adsorption on the MIP core-shell particles.
A miniaturised optical assembly for low-light fluorescence measurements was also developed. Based on small opto-electronic parts and optical fibres, the emission from the MIP particles upon addition of pY concentrations from 0.5-200 μM could be monitored in real-time.
The reliable identification and quantification of phosphorylated amino acids, peptides and proteins is one of the key challenges in contemporary bioanalytical research, noteworthy, to diagnose and treat diseases at an early developmental stage. Miniaturised sensing devices like microfluidic chips combined with “smart” detection chemistry, simple data assessment, processing and presentation are very attractive for benchtop use in clinical environments.
We developed novel synthetic probes targeting phosphorylated amino acids, based on core-shell microparticles consisting of a silica core coated with a molecularly imprinted polymer (MIP) shell. These “plastic antibodies” are extremely robust, resist denaturing solvents and elevated temperatures, can be reproducibly produced at low cost, and potentially overcome many of the practical problems in current bioanalytical detection strategies. The MIP layer contains a fluorescent probe monomer, binds selectively to phosphorylated tyrosine (pTyr) with a significant imprinting factor higher than 3.5 and responds with a “lighting-up” of its fluorescence accompanied by the development of a strongly red-shifted emission band toward the analyte.
In analogy to our previous work [4], the bead-based ratiometric detection scheme has also been successfully transferred to a microfluidic chip format to demonstrate its applicability to rapid assays. Such a miniaturised device could yield an automated pTyr measurement system in the future. The setup was built by coupling a modular microfluidic system [5] for amino acid functionalisation (Fmoc protection) and a multi-layer PDMS/Teflon/glass microfluidic chip [6] for buffering, extraction (micropillars co-flow extraction) and selective adsorption on the MIP core-shell particles.
A miniaturised optical assembly for low-light fluorescence measurements was also developed. Based on small opto-electronic parts and optical fibres, the emission from the MIP particles upon addition of pTyr concentrations from 0.5 – 200 μM could be monitored in real-time.
High-resolution mass spectrometry, either combined with gas or liquid chromatography (GC/LC-HR-MS), is currently the most powerful analytical option for broad nontargeted small molecule analysis. To transform HR-MS raw data from metabolomics or environmental studies into chemically meaningful data, several computational steps are needed, including peak detection, deconvolution of these peaks into compounds and putative identification of compounds using databases. Each of these steps can cause problems and still requires methodological advancements. Computational compound annotation as one of the steps, however, has proven particularly challenging, mainly due to the chemical diversity of organic analytes. In addition, different annotation approaches are needed for the different platforms used in HR-MS screening. We recently introduced InterpretMSSpectrum as an annotation workflow for GC-HR-MS using atmospheric pressure chemical ionization (APCI). InterpretMSSpectrum locates molecular ion, fragment and adduct peaks, calculates their most likely sum formula combination and graphically summarizes results as an annotated mass spectrum. As a complementary approach for LC-HR-MS, we presented findMAIN, which scores MS1 spectra based on explained intensity, mass accuracy and isotope charge agreement of adducts and related electrospray ionization (ESI) products to determine the neutral mass of unknown compounds. Both approaches were validated against large spectral libraries containing more than 600 compounds, for which correct annotation was achieved in over 80% of the cases. Based on the experiences from this validation, we here compare soft-ionization GC/LC-HR-MS regarding “annotatability” of unknown compounds from a computational perspective. As a main advantage for GC-HR-MS, the relatively uniform ionization behavior of commonly used trimethylsilyl (TMS) derivatives observed under APCI allowed differentiation of molecular ion peaks from in-source fragments based on relatively compact set of rules. By contrast, neutral mass inference in ESI required a more complex evaluation scheme, due to the higher diversity of ionization products observable in ESI. We demonstrate such differences by practical examples of both software packages applied to metabolomics studies and discuss the challenges connected to transferring the approaches to environmental screening.
Bacterial samples are typically freeze dried or cryo-prepared prior to XPS analysis to allow for measurements in ultra-high vacuum (UHV). The sample environment in the near-ambient pressure (NAP) XPS instrument EnviroESCA allows for measurements in up to 15 mbar water vapor, thus, sample preparation is no longer restricted to UHV-compatible techniques. For instance, biofilms grown in medium can be transferred directly from the medium to the measurements chamber, maintaining a humid environment throughout the measurements. Considering the complexity of bacterial samples, sample preparation must be carefully considered in order to obtain meaningful and reproducible results.
In this talk, various strategies for sample preparation of bacteria and biofilms for NAP-XPS measurements will be discussed. Model systems of planktonic bacteria, artificial biofilms resembling the exopolysaccharide matrix and biofilms have been characterised in various conditions. The stability and homogeneity of the samples was assessed by monitoring the C1s core level peak at different sample locations. The quality of the XPS-spectra is also influenced by the gas environment, which will be exemplified by core level spectra of P. Fluorescens acquired in air, water vapor and ultra-high vacuum.
Core-shell nanoparticles (CSNPs) have become indispensable in various industrial applications. However, their real internal structure usually deviates from an ideal core-shell structure. To control how the particles perform with regard to their specific applications, characterization techniques are required that can distinguish an ideal from a non-ideal morphology. In this work, we investigated PTFE-PMMA (four samples) and PTFE-PS (six samples) polymer CSNPs with constant core diameter (45 nm) but varying shell thickness (4-50 nm). As confirmed by transmission scanning electron microscopy (T-SEM), the shell completely covers the core for the PTFE-PMMA nanoparticles, while the encapsulation of the core by the shell material is incomplete for the PTFE-PS nanoparticles. X-ray photoelectron spectroscopy (XPS) was applied to determine the shell thickness of the nanoparticles. The software SESSA V2.0 was used to analyze the intensities of the elastic peaks and the QUASES software package to evaluate the shape of the inelastic background in the XPS Survey spectra.
For the first time, nanoparticle shell thicknesses are presented which are exclusively based on the analysis of the XPS inelastic background. Furthermore, principal component analysis (PCA) assisted time-of-flight secondary ion mass spectrometry (ToF-SIMS) of the PTFE-PS nanoparticle sample set revealed a systematic variation among the samples and, thus, confirmed the incomplete encapsulation of the core by the shell material. Opposed to that, no variation is observed in the PCA scores plots of the PTFE-PMMA nanoparticle sample set. Consequently, the complete coverage of the core by the shell material is proved by ToF-SIMS with a certainty that cannot be achieved by XPS and T-SEM.
Im Vortrag werden Anforderungen und Lösungsvorschläge für das Labor der Zukunft diskutiert. Industrie 4.0 bzw. das Labor 4.0 hilft uns, komplexere Prozesse schneller umzusetzen. Entwicklung von Anlagen und Prozessen beginnt im Labor 4.0. Dazu werden offene, nicht proprietäre Schnittstellen und Standards bei Laborgeräten und Feldgeräten dringend benötigt.
Using a swarm of copter-based gas-sensitive aerial nano robots for monitoring indoor air quality is challenging due to, e.g., limited air space in buildings. To avoid an over-regulation of the available indoor air space (e.g., prohibit copters to fly above each other), a safety region around each copter must be defined to guarantee a safe operation of the swarm.
The key contributions of this poster are the realization of experiments that investigate the influence of the rotor downwash on flying vertically displaced nano robots and the development of a model describing the above-mentioned safety region.