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Real Time Imaging of Deuterium in a Duplex Stainless Steel Microstructure by Time-of-Flight SIMS
(2016)
For more than one century, hydrogen assisted degradation of metallic microstructures has been identified as origin for severe technical component failures but the mechanisms behind have not yet been completely understood so far. Any in-situ observation of hydrogen transport phenomena in microstructures will provide more details for further elucidation of these degradation mechanisms. A novel experiment is presented which is designed to elucidate the permeation behaviour of deuterium in a microstructure of duplex stainless steel (DSS). A hydrogen permeation cell within a TOF-SIMS instrument enables electrochemical charging with deuterium through the inner surface of the cell made from DSS. The outer surface of the DSS permeation cell exposed to the vacuum has been imaged by TOF-SIMS vs. increasing time of charging with subsequent chemometric treatment of image data. This in-situ experiment showed evidently that deuterium is permeating much faster through the ferrite phase than through the austenite phase. Moreover, a direct proof for deuterium enrichment at the austenite-ferrite interface has been found.
To understand the metabolic fate of food relevant mycotoxins in vitro systems were mainly used as the method of choice, so far. Yet, in recent years coupling of electrochemistry mass spectrometry (EC-MS) gained increasing importance as promising technique for fast simulation of metabolic processes and was successfully applied in particular for drug metabolism [1].
The aim of our work was to investigate the potential of EC-MS to predict phase I metabolites of priority mycotoxins and to compare the results with in vitro experiments. Hence, the EU-regulated Fusarium mycotoxins zearalenone (ZEN) and patulin as well as dihydroergocristine (DHEC) as model compound of ergot alkaloids were electrochemically oxidized and analyzed by EC MS for the first time.
Electrochemical conditions were set-up individually for each of the three mycotoxins. By using a coulometric flow through cell with a diamond working electrode oxidation of the chosen mycotoxins was observed after applying potentials between 1.7 and 2.0 V vs. Pd/H2. The electrochemically generated reaction products were analyzed online by mass-spectrometric detection.
All of the three chosen mycotoxins were electrochemically converted to mono- and/or dihydroxylated products confirming the results of ZEN related metabolism studies [2, 3] and in case of DHEC own results from in vitro assays. Due to a lack of metabolism studies concerning the oxidative fate of patulin, interpretation of EC-MS data and performing microsomal studies is of particular relevance.
Beside the identified products from electrochemical oxidation of ZEN, patulin and DHEC there is still a number of yet unknown compounds. Additional structural characterization of detected compounds by NMR and X-ray analysis will be facilitated by their large-scale production using preparative EC cells.
Lead (Pb) isotope amount ratios are commonly used in applications ranging from archaeology and forensic sciences to terrestrial and extra-terrestrial geochemistry. Despite their utility and frequency of use, only three certified isotope amount ratio reference materials are currently available for Pb: NIST SRMs 981, 982 and 983. Because SRM 981 has a natural Pb isotopic composition, it is mainly used for correcting instrumental mass discrimination or fractionation. This means that, at present, there are no other certified isotope reference materials with natural Pb isotopic composition that could be used for validating or verifying an analytical procedure involving the measurement of Pb isotope amount ratios.
To fill this gap, two new reference materials, both certified for their Pb isotopic composition, have been produced together with a complete uncertainty assessment. These new reference materials offer SI traceability and an independent means of validating or verifying analytical procedures used to produce Pb isotope amount ratio measurements.
ERM-EB400 is a bronze material containing a nominal Pb mass fraction of 45 mg/kg. ERM-AE142 is a high purity solution of Pb with a nominal mass fraction of 100 mg/kg. Both materials have been specifically produced to assist analysts in verifying or validating their analytical procedures. Note that while one of these reference materials requires the chemical separation of Pb from its matrix (ERM-EB400), the other does not (ERM-AE142). Details on the certification of these isotope reference materials are provided in this report.
Real time monitoring of chemical reactions has become a key step in industrial processes due to constantly increasing demands on product performance and environmental compatibility. In contrast to spectroscopic methods that usually require sample pretreatment, mass spectrometry (MS) has been proven as a robust method for multicomponent analysis. As an especially demanding reaction process, we here report successfully on the entirely contactless conduction and interrogation of a chemical reaction inside an acoustically levitated microliter droplet of reaction mixture. The approach represents a proof of concept study for fast reaction optimization approaches with minimal resource consumption. The sampling is done by repeated laser desorption of small fractions of the droplets volume spread over the timescale of the reaction process.
The upscaling from small scale academic reactors to large industrial processes typically suffers from a large change in surface-to-volume ratio. A promising approach is the general avoidance of surfaces as in levitated droplet techniques. However, up to now, no mass spectrometric interface for online reaction monitoring in levitated droplets has been provided.
As model reaction the photoinitiated thiol-ene coupling between N-boc cysteine methyl ester and allyl alcohol was studied. A droplet of 5 µL reactand solution was provisioned into an acoustic trap aligned lateral to the MS inlet. Contactless sampling by laser ablation (LA) is followed by dielectric barrier discharge (DBD) postionization. The latter is needed to address non polar reaction partners.
Mycotoxins can be found worldwide in food and feed and cause a variety of mold-related health risks which makes it necessary to further examine their metabolic fate in human and other mammals. Beside standard in vitro assays with liver cell preparations an increasing interest in new simulation methods are playing a growing role. The online coupling of electrochemistry with mass spectrometry (EC/MS) is one of these novel techniques, successfully applied in pharmacological and drug research for several years now. The primary objective of this study was to investigate the capability of EC/MS to elucidate metabolic pathways of the mycotoxin citrinin as relevant food contaminant. For this purpose, a coulometric flow through cell equipped with a glassy carbon working electrode was used by applying a ramped potential between 0 and 2 V vs Pd/H2. The electrochemically generated oxidation products analyzed by EC/MS were compared to those obtained from in vitro assays. To receive a comprehensive assessment of EC/MS other non-microsomal oxidation techniques such as Fenton-like reaction and UV irradiation were applied. Several hydroxylated derivatives of citrinin were generated by EC/MS and Fenton-like reaction which are similar to microsomal biotransformation products. These data show that EC/MS is a versatile tool that can be easily applied in mycotoxin research to support metabolic investigations of known and unknown mycotoxins.
Copolymer structure elucidation by multidimensional techniques with focus on UPLC x ESI-TOF-MS
(2017)
Structure elucidation of complex synthetic copolymers still represents a challenge. An one-dimensional separation technique cannot give the answer to the question: What are the molar mass distribution (MMD), the functionality distribution (FTD), the chemical composition distribution (CCD), the monomer sequence distribution (MSD), the topology differences within a single broad distributed polymer sample?
Since the first LC/ ESI-MS experiment of the Nobel prize winner John B. Fenn in 1984, the coupling of liquid chromatographic to mass spectrometric techniques gained a continuous rapid development.
Often the deficiencies of stand-alone methods can be bridged. LC, blind to structural information needs mass spectrometry as one of the most powerful detectors able to give detailed information on e.g. the repeat units, functionalization or copolymer composition of the chromatographic separated constituents. A separation prior to MS reduces radical the dispersity which is one of the reasons for failing of MS. Also problems with different ionization probabilities in complex mixtures can partly be overcame.
Different LC separation techniques as size exclusion chromatography (SEC), liquid adsorption chromatography (LAC), liquid chromatography at critical conditions (LCCC) and gradient elution liquid chromatography (GELC) combined with Matrix assisted Laser Desorption Ionization (MALDI) respectively Electrospray Ionization (ESI) Time of Flight (TOF) mass spectrometry are able to give information which otherwise are completely inaccessible. In some cases CID tandem mass spectrometry is applied. Fragmentation of suitable precursor ions resulted in typical fragment ion patterns. This technique enables an additional information on e.g. sequences, structural defects and topology of complex polymer mixtures.
Herein a new approach is demonstrated to provide evidence of different functionalities and short block sequences in statistical EO-PO copolymers. Furthermore silsesquioxane mixtures and Polyglycerols are investigated concerning occurring topology effects.
Recently, a novel ionization scheme for ambient MS has been introduced. It is based on a quasi-continuous laser induced plasma (LIP), ignited in front of the MS inlet. This setup comprises the advantages of an ambient probe, electro neutrality, a sufficient duty cycle, a ubiquitous plasma medium, low power consumption, the absence of solvents and high sensitivity. To assess its future applicability for the detection of volatile organic compounds, plasma properties and operating conditions are investigated to understand the processes, that lead to the unexpected formation of intact molecular ions. Comprehensive studies include optical Emission spectroscopy, shadowgraphic shockwave visualization and time-of-flight mass spectrometry.
A novel ionization scheme for ambient mass spectrometry is presented and discussed. Desorption and ionization are achieved by a quasi-continuous laser induced plasma (LIP) ignited in front of the atmospheric pressure interface of a time-of-flight mass spectrometer. This setup comprises the advantages of i) an ambient probe, ii) electro neutrality, iii) low power consumption, iv) a sufficient duty cycle, v) a ubiquitous plasma medium (air) and vi) high sensitivity caused by the high electron number densities.
The plasma properties and operating conditions are investigated to understand the processes that lead to the formation of molecular ions. Comprehensive studies include optical emission spectroscopy, shadowgraphic shockwave visualization and time-of-flight mass spectrometry investigations. The observed MS signal (including reagent-ion signal, as well as analyte spectra) closely resembles the ionization behavior of other electrically-driven plasma-based ionization sources, such as DBD, LTP or DART. Conversely that means that although LIPs are commonly known to have temperatures way above 10.000 K and thus efficiently atomize and ionize molecules, MS spectra were obtained that showed the formation of intact molecular ions.
For an insight into the LIP properties the optical emission of the LIP is examined and exhibits a pronounced degree of dissociation into atomic and ionic species, which reflects the higher temperature and electron density inside a LIP. Accordingly, rather elemental (ICP-type) than molecular spectra should be expected. However due to the absence of such ions, we conclude that the analyte does not enter the hot center of the plasma itself. Moreover, the initial, highly-excited plasma species react cascade-like to lower energetic species via reactive collision with the surrounding atmosphere, which can then subsequently ionize molecules of interest. The concept potentially involves charge transfer, proton transfer, electron impact and photoionization.
These assumptions are confirmed via the shadowgraphs of the expanding shockwave around the LIP. An effective spatial separation between the two regions is maintained by concentrically expanding pressure waves resulting in a strongly unidirectional diffusion. Additionally, the strictly outbound matter transport suggests a rarefaction inside the plasma region for each plasma event.
A novel ionization scheme for ambient mass spectrometry is presented and discussed. Desorption and ionization are achieved by a quasi-continuous laser induced plasma (LIP) ignited in front of the atmospheric pressure interface of a time-of-flight mass spectrometer. This setup comprises the advantages of i) an ambient probe, ii) electro neutrality, iii) low power consumption, iv) a sufficient duty cycle, v) a ubiquitous plasma medium (air) and vi) high sensitivity caused by the high electron number densities.
The plasma properties and operating conditions are investigated to understand the processes that lead to the formation of molecular ions. Comprehensive studies include optical emission spectroscopy, shadowgraphic shockwave visualization and time-of-flight mass spectrometry investigations. The observed MS signal (including reagent-ion signal, as well as analyte spectra) closely resembles the ionization behavior of other electrically-driven plasma-based ionization sources, such as DBD, LTP or DART. Conversely that means that although LIPs are commonly known to have temperatures way above 10.000 K and thus efficiently atomize and ionize molecules, MS spectra were obtained that showed the formation of intact molecular ions. For an insight into the LIP properties the optical emission of the LIP is examined and exhibits a pronounced degree of dissociation into atomic and ionic species, which reflects the higher temperature and electron density inside a LIP. Accordingly, rather elemental (ICP-type) than molecular spectra should be expected. However due to the absence of such ions, we conclude that the analyte does not enter the hot center of the plasma itself. Moreover, the initial, highlyexcited plasma species react cascade-like to lower energetic species via reactive collision with the surrounding atmosphere, which can then subsequently ionize molecules of interest. The concept potentially involves charge transfer, proton transfer, electron impact and photoionization.
These assumptions are confirmed via the shadowgraphs of the expanding shockwave around the LIP. An effective spatial separation between the two regions is maintained by concentrically expanding pressure waves resulting in a strongly unidirectional diffusion. Additionally, the strictly outbound matter transport suggests a rarefaction inside the plasma region for each plasma event.