matrix-assisted laser/desorption ionization time-of-flight (MALDI-TOF) mass spectrometry

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Identification of Adult Fasciola spp. Using Matrix-Assisted Laser/Desorption Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry

Identification of Adult Fasciola spp. Using Matrix-Assisted Laser/Desorption Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry

Abstract: Fascioliasis is a neglected trematode infection caused by Fasciola gigantica and Fasciola hepatica. Routine diagnosis of fascioliasis relies on macroscopic identification of adult worms in liver tissue of slaughtered animals, and microscopic detection of eggs in fecal samples of animals and humans. However, the diagnostic accuracy of morphological techniques and stool microscopy is low. Molecu- lar diagnostics (e.g., polymerase chain reaction (PCR)) are more reliable, but these techniques are not routinely available in clinical microbiology laboratories. Matrix-assisted laser/desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) is a widely-used technique for identification of bacteria and fungi; yet, standardized protocols and databases for parasite detection need to be developed. The purpose of this study was to develop and validate an in-house database for Fasciola species-specific identification. To achieve this goal, the posterior parts of seven adult F. gigantica and one adult F. hepatica were processed and subjected to MALDI-TOF MS to create main spectra profiles (MSPs). Repeatability and reproducibility tests were performed to develop the database. A principal component analysis revealed significant differences between the spectra of F. gigantica and F. hepatica. Subsequently, 78 Fasciola samples were analyzed by MALDI-TOF MS using the previously developed database, out of which 98.7% (n = 74) and 100% (n = 3) were correctly identified as F. gigantica and F. hepatica, respectively. Log score values ranged between 1.73 and 2.23, thus indicating a reliable identification. We conclude that MALDI-TOF MS can provide species-specific identification of medically relevant liver flukes.
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Characterization of Yersinia using MALDI-TOF mass spectrometry and chemometrics.

Characterization of Yersinia using MALDI-TOF mass spectrometry and chemometrics.

enterocolitica, Yersinia pseudotuberculosis, and Yersinia pestis, are pathogenic in humans. Rapid and accurate identification of Yersinia strains is essential for appropriate therapeutic management and timely intervention for infection control. In the past decade matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) in combination with computer-aided pattern recognition has evolved as a rapid, objective, and reliable technique for microbial identification. In this comprehensive study a total of 146 strains of all currently known Yersinia species complemented by 35 strains of other relevant genera of the Enterobacteriaceae family were investigated by MALDI-TOF MS and chemometrics. Bacterial sample preparation included microbial inactivation according to a recently developed mass spectrometry compatible inactivation protocol. The mass spectral profiles were evaluated by supervised feature selection methods to identify family-, genus-, and species- specific biomarker proteins and—for classification purposes—by pattern recognition techniques. Unsupervised hierarchical cluster analysis revealed a high degree of correlation between bacterial taxonomy and subproteome-based MALDI-TOF MS classification. Furthermore, classification analysis by supervised artificial neural networks allowed identification of strains of Y. pestis with an accuracy of 100%. In-depth analysis of proteomic data demonstrated the existence of Yersinia-specific biomarkers at m/z 4350 and 6046. In addition, we could also identify species-specific biomarkers of Y.
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Sample preparation of formalin-fixed paraffin-embedded tissue sections for MALDI-mass spectrometry imaging

Sample preparation of formalin-fixed paraffin-embedded tissue sections for MALDI-mass spectrometry imaging

Received: 6 October 2019 / Revised: 6 November 2019 / Accepted: 20 November 2019 / Published online: 28 January 2020 # The Author(s) 2020 Abstract Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MALDI MSI) has become a powerful tool with a high potential relevance for the analysis of biomolecules in tissue samples in the context of diseases like cancer and cardiovascular or cardiorenal diseases. In recent years, significant progress has been made in the technology of MALDI MSI. However, a more systematic optimization of sample preparation would likely achieve an increase in the molecular information derived from MALDI MSI. Therefore, we have employed a systematic approach to develop, establish and validate an optimized “standard operating protocol” (SOP) for sample preparation in MALDI MSI of formalin-fixed paraffin-embedded (FFPE) tissue sample analyses within this study. The optimized parameters regarding the impact on the resulting signal-to-noise (S/N) ratio were as follows: (i) trypsin concentration, solvents, deposition method, and incubation time; (ii) tissue washing procedures and drying processes; and (iii) spray flow rate, number of layers of trypsin deposition, and grid size. The protocol was evaluated on interday variability and its applicability for analyzing the mouse kidney, aorta, and heart FFPE tissue samples. In conclusion, an optimized SOP for MALDI MSI of FFPE tissue sections was developed to generate high sensitivity, to enhance spatial resolution and reproducibility, and to increase its applicability for various tissue types. This optimized SOP will further increase the molecular information content and intensify the use of MSI in future basic research and diagnostic applications.
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Atmospheric Pressure Desorption by Impulsive Vibrational Excitation Mass Spectrometry (AP-DIVE-MS)

Atmospheric Pressure Desorption by Impulsive Vibrational Excitation Mass Spectrometry (AP-DIVE-MS)

2.1. Picosecond Infrared Laser (PIRL) 37 der atmospheric condition and termed the method picosecond infrared laser ablation electrospray ionization (PIR-LAESI). The method used an ESI nebulizer to combine PIRL ablation plume for post-ionization with a home-constructed imaging system with a vertical resolution of 20-30 µm and lateral resolution of around 100 µm. The sensitivity of the system was measured to be 25 fmol of Rhodamine in agar and a limit of detection of ∼ 100 nM for reserpine and ≥ 5nM for verapamil aqueous solu- tions [24]. Moreover, they performed molecular dynamics simulations of the PIRL ablation process by using a model peptide (lysozyme)/counterion system in aqueous solution under typical experimental conditions in TOF-MS. The results showed that over 90% of the water molecules were stripped off from lysozyme within 1 ns after PIRL ablation without fragmentation. In addition, the applied field had almost no influence on the laser ablation and desorption process; yet there was sign even at very early time (limits of the MD simulation) that applied fields can be used to sepa- rate native charged proteins from their counterions, eliminating any post -ionization requirements and allowing the studying of mixtures without purification. This work demonstrated the potential of PIRL as a desorption source for high sensitivity quan- titative MS [79].
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Gutenberg Open Science: Characterisation and field deployment of a novel quantitative Time-of-Flight Aerosol Mass Spectrometer (ToF-AMS)

Gutenberg Open Science: Characterisation and field deployment of a novel quantitative Time-of-Flight Aerosol Mass Spectrometer (ToF-AMS)

One advantage of LDI aerosol mass spectrometry is that two mass spectrometers can be used in parallel, configured to extract ions with opposite polarities from the desorption region (Hinz et al., 1996). This means that positive and negative mass spectra for individual particles can be captured simultaneously, increasing the amount of information obtained. Laser-based aerosol mass spectrometers are proving to be powerful and unique tools with a large number of applications (Suess and Prather, 1999). However, while qualitative information on the chemical composition of aerosols can be obtained, providing quantitative data with LDI represents an intrinsic problem. On the one hand, LDI methods that employ high laser fluence (laser power density) can produce extensive fragmentation of molecules and quantitative information on the elementary composition can therefore be obtained (Reents and Schabel, 2001), although information on the molecular structure cannot be obtained. On the other hand, when employing lower fluences, less fragmentation occurs, allowing more chemical information to be obtained. At the same time the particle components are not necessarily fully vaporised or inonised by the laser pulse and are therefore detected with varying efficiency depending on the particle’s size and chemical composition. Furthermore, incomplete vaporisation makes ionisation more sensitive to species present on the surface than those in the core (Allen et al., 2000; Kane and Johnston, 2000). In addition, individual chemical components can interact with each other during the desorption and ionisation process, resulting in an uneven distribution of charges between the fragments. This is known as ‘matrix effect’ (Reilly et al., 2000). Finally, spectral intensities depend not only on the laser power density absorbed by the molecules, but also on the instrument sensitivity to specific species. This in turn depends on the absorption characteristics of the individual species present in the sample under study (Gross et al., 2000).
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Enhanced analysis of stratified climate archives through upgrade of Laser Ablation Inductively Coupled Plasma Quadrupole to Time of Flight Mass Spectrometry?

Enhanced analysis of stratified climate archives through upgrade of Laser Ablation Inductively Coupled Plasma Quadrupole to Time of Flight Mass Spectrometry?

Reflected ions reach the detector through the secondary drift tube. It consists of two micro channel plates in chevron arrangement (Wiza, 1979) (Figure 8). The channel matrix is fabricated from a boron silicate glass treated in such a way that the walls are semiconducting. Parallel electrical contact to each channel is provided by the deposition of a metallic coating, which then serve as input and output electrodes, respectively. Every ion which hits the channel plates’ surface releases electrons which are accelerated and creates secondary electrons until finally an electron avalanche reaches the anode surface. Thereby an electrical pulse is released, which is counted after pre-amplifying (detection pulse). The time between repeller pulse (start) and detection pulse (arrival) is the measure for the mass of an ion. The storage of one detection pulse takes 1 ns. In the presented experimental setup the analysis of one complete mass spectrum takes 34 Ps up to mass 285 amu. If each ns data are stored, the spectrum consists of 34000 data points. Each time a channel has to process an incoming ion this channel needs 3 – 4ms to recover (pers. comm. R. Müller, SI Scientific Instr. GmbH, 2008), whereas the flight time of neighbouring isotopes lay within the ns range. This may lead to problems if element concentrations of a sample are high. More detailed information are given by Hoffmann et al. (2002, 2005) or can be received by Analytik Jena, the distributor of the ICP-TOF-MS system.
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Improved matrix coating for positive- and negative-ion-mode MALDI-TOF imaging of lipids in blood vessel tissues

Improved matrix coating for positive- and negative-ion-mode MALDI-TOF imaging of lipids in blood vessel tissues

Mass spectrometry imaging (MSI) has become a powerful tool for the analysis of biological tissue, in particular due to its potential to monitor 2D distributions of chemicals in dif- ferent tissue layers [ 1 – 3 ]. In matrix-assisted laser desorption/ ionization mass spectrometry imaging (MALDI MSI), the fabrication of a homogeneous, analyte containing matrix coat- ing [ 4 ] is a prerequisite for high sensitivity but also the key step for the acquisition of highly resolved data. This can be achieved by either applying a matrix in solution [ 5 – 10 ] or depositing solvent-free matrix onto the sample surface [ 11 – 15 ]. Although the application of a dissolved matrix (usu- ally using an automated spray system [ 16 ]) features an imme- diate orthogonal integration of the analytes into the matrix, it involves the risk of lateral analyte delocalization, which is a clear limitation for high-resolution imaging. On the other side,
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Quantification of nitroaromatic explosives in contaminated soil using MALDI-TOF mass spectrometry

Quantification of nitroaromatic explosives in contaminated soil using MALDI-TOF mass spectrometry

Ion mobility spectrometry is often applied for the field detection of explosives and is widely used for the detection of trace levels of nitroaromatic explosives at airports [ 11 ]. Small handheld and user-friendly devices are available that allow real-time monitoring and have higher sensitivity than mass spectrometry (MS) technologies [ 12 ]. On the other hand, ion mobility spectrometry has lower selectivity, a limited lin- ear range, and low resolution [ 12 ]. Besides, high concentra- tions of explosives and complex matrices may lead to satura- tion and contamination of the instrument, which causes inter- ferences in quantitative determinations [ 12 , 13 ]. Most com- monly, high-performance liquid chromatography (HPLC) with UV detection or MS is used for the quantification of nitroaromatic explosives on contaminated sites [ 14 ]. Despite the advantage of very sensitive detection, liquid chromatogra- phy (LC)–MS is associated with high costs and lengthy sam- ple analysis and requires well-qualified staff [ 14 ]. Conversely, matrix-assisted laser desorption/ionization (MALDI) time-of- flight (TOF) MS is simple, tolerant of sample impurities, and fast, needs small sample volumes, and can be automated eas- ily, which is a fundamental requirement for high-throughput applications [ 15 ]. Originally, MALDI-TOF MS was most fre- quently used for the qualitative analysis of high molecular weight compounds, such as proteins, peptides, polymers, and even prokaryotic or eukaryotic cells [ 15 , 16 ]. In contrast, the analysis of low molecular weight compounds or quantifi- cation of substances was not the focus of research because the organic matrix often leads to the suppression of analyte peaks in the low mass range [ 15 ]. However, in recent years several approaches using new matrix substances increased the appli- cability of MALDI-TOF MS for small molecules, such as oligosaccharides, phospholipids, peptides, metabolites, drugs, and environmental contaminants [ 17 – 22
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MALDI imaging mass spectrometry in clinical proteomics research of gastric cancer tissues

MALDI imaging mass spectrometry in clinical proteomics research of gastric cancer tissues

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry, or MALDI imaging, is a powerful tool for investigating protein patterns through the direct (in situ) analysis of tissue sections [5]. Similarly to immunohistochemistry, MALDI imaging has advantages over other assay methods (i.e., those requiring homogenization) because it is morphology driven [98]. This characteristic allows to directly evaluate tumor cells, to determine correlations with other morphologic features, and to assay smaller patient tumor tissue specimens, such as surgical or endoscopic biopsy specimens [79]. These features make it an interesting tool for tissue analysis and molecular histology [99]. In addition, MALDI imaging can determine the distribution of hundreds of compounds in a single measurement without any need for labeling [100]. The great potential of a highly sensitive and molecularly specific technology such as MALDI imaging to the field of oncology is currently being realized. Until now, this technique has been successfully applied to various types of cancer tissues, including human non-small cell lung cancer, gliomas, and ovarian, prostate, and breast cancer [69, 70, 72, 101-103]. Analysis of the resulting complex mass spectrometry data sets using modern biocomputational tools has resulted in the identification of both disease state, response prediction, and patient prognosis- specific protein patterns [69-71].
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Untersuchungen zur Anwendbarkeit der "Matrix-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry" - Technik für die Identifikation von klinisch relevanten, coryneformen Bakterien

Untersuchungen zur Anwendbarkeit der "Matrix-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry" - Technik für die Identifikation von klinisch relevanten, coryneformen Bakterien

Für den Vergleich der Identifikationssysteme API Coryne und MALDI-TOF MS wurden 509 Isolate coryneformer Bakterien in der Routinediagnostik des MVZ Labor Dr. Gärtner & Kollegen, Ravensburg, im Zeitraum von Ende November 2009 bis Ende Februar 2010 gesammelt. Nach Probeneingang wurden die Probenmaterialien im Rahmen der Routine- diagnostik aufgearbeitet. Coryneforme Bakterien wurden anhand ihres Wachstums auf grampositiven Selektivmedien, der Morphologie der Bakterienkolonien, gegebenenfalls durch Gramfärbung und gegebenenfalls durch Testung der Katalase-Reaktion vor- identifiziert. Anschließend wurde mit einer Reinkultur der coryneformen Bakterien ein API Coryne Teststreifen (bioMérieux, Marcy l`Etoile, Frankreich) beimpft.
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Erwinia species identification using matrix-assisted laser desorption ionization-time of flight mass spectrometry

Erwinia species identification using matrix-assisted laser desorption ionization-time of flight mass spectrometry

In the last two decades, whole cell Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spec- trometry (MALDI-TOF MS) has emerged as a reliable tool for rapid microbial identification in clinical diagnostics (Dierig et al., 2015; Patel, 2013). Identification is based on unique mass/charge ratio (m/z) fingerprints of proteins, which are ionized using short laser pulses directed to sub- colony amounts of whole (“intact”) bacterial cells embed- ded in a matrix. After desorption, ions are accelerated in vacuum by a strong electric potential and separated on the basis of their time of flight to the detector, which is proportional to the mass-to-charge ratio. The main benefit of this technique with respect to conventional molecular biological tools resides in the straightforward preparation of the samples, which can commonly be completed in less than a minute directly from a single bacterial colony, and in the fact that it does not require any a priori knowledge of the organism to be investigated. This technique has proven itself reliable across a broad range of conditions, being relatively unaffected by factors such as the cell- growth phase or the composition of the culture medium, thus displaying limited variability in mass-peak signatures within the typically designated mass range between 2,000 and 20,000 Daltons (Lay, 2001; Maier et al., 2006; Rezzo- nico et al., 2010). These features make whole cell MALDI- TOF MS an easy, rapid and cost-effective technique, which is extraordinarily suited for high-throughput routine anal- ysis (Seng et al., 2009).
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Anwendbarkeit der Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) für den Nachweis und die Differenzierung von Leptospira spp. im Vergleich zum Multilocus Sequence Typing (MLST)

Anwendbarkeit der Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) für den Nachweis und die Differenzierung von Leptospira spp. im Vergleich zum Multilocus Sequence Typing (MLST)

Stationärenphase befinden, verwendet werden dürfen, da die Proteine der Probe nur in diesen Phasen stabil exprimiert werden. Zudem ist für eine erfolgreiche Messung eine Mindestzahl von 10 5 bis 10 7 Bakterienzellen pro Messung notwendig um eine genügend hohe Proteindichte zu erhalten. Kontaminationen oder Mischkulturen führen zu qualitativ minderwertigen Massenspektren, die keine sichere Speziesidentifikation erlauben. Daher sollte für die weitere Bearbeitung nur eine Reinkolonie pro zu messenden Spot verwendet werden (FREIWALD et al., 2009). Für die Proteinextraktion stehen, je nach verwendetem Ausgangsmaterial, verschiedene Protokolle zur Verfügung. Die am häufigsten angewendete Methode ist der direkte Transfer einer Bakterienkolonie auf einen Spot des Targets. Die anschließende Überschichtung mit der Matrix inaktiviert die Bakterienzellen. Für anspruchsvollere Keime oder hochpathogene Erreger und Sporenbildner werden die Ethanol-Ameisensäure-Extraktion oder die Triflouressigsäure-Extraktion empfohlen. Für Erstere ist eine höhere Dichte von 10 6 bis 10 7 Bakterienzellen notwendig (FREIWALD et al., 2009). Allgemein gilt, dass mit extrahierten Proben qualitativ bessere Spektren generiert werden können als mit direkt geschmierten Proben. Die gemessenen Spektren werden anschließend softwarebasiert mit denen in einer Referenzdatenbank hinterlegten Proteinspektren abgeglichen (ALATOOM et al., 2011). Diese umfasst eine große Anzahl (derzeit 4642) klinisch relevanter bakterieller Isolate. Für den Abgleich wird ein numerischer Wert, der sogenannte score value, errechnet und so die Übereinstimmung des gemessenen Analyten mit dem Spektrum in der Datenbank analysiert. Je nach errechnetem Wert ist eine sichere Differenzierung auf Genus- oder Speziesebene möglich (WIESER et al., 2011). Die Reproduzierbarkeit eines Ergebnisses hängt dabei vor allem von der Qualität der Referenzdatenbank ab. Dazu sollte für jede hinterlegte Spezies ein Massen- spektrum vorhanden sein, wobei eine Spezies von mehreren Stämmen in der Datenbank repräsentiert werden sollte (WELKER (2), 2011). Empfohlen werden mindestens zehn Stämme pro Spezies (ROSSELLO-MORA et al., 2001). Durch die Aufnahme mehrerer Spektren einer Spezies in die Datenbank können die Unterschiede nahe verwandter Arten besser dargestellt und dadurch bessere Ergebnisse erzielt werden (ALATOOM et al., 2011).
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Determination of true ratios of different N-glycan structures in electrospray ionization mass spectrometry

Determination of true ratios of different N-glycan structures in electrospray ionization mass spectrometry

A solution to the problem is the use of internal standards labeled without alteration of the overall structure, which has recently been presented in the form of 1 3 C-labeled N-acetylated glycans [ 30 ]. A range of glycan structures cov- ering the species relevant for the analysis of monoclonal anti- bodies was prepared, including a disialylated glycan. Many glycoproteins, however, contain trisialylated and tetrasialylated N-glycans, and in our experience and that of others these more complex glycans show the strongest devia- tions of molar response [ 32 – 34 ]. Preparation of isotopically labeled glycans of this complexity, however, becomes a highly demanding task, and hence the resulting standard mixtures would be too expensive for routine use. Therefore, Mehta et al. [ 35 ] concentrated on a set of three natural glycans with zero or two sialic acids for the analysis of permethylated gly- cans by nanospray MS and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MS [ 35 ]. Both strat- egies yield absolute quantitation and hence also true relative proportions of the glycans considered. For characterization of biopharmaceutical glycoproteins, relative quantitation appears to be the more relevant task, which is particularly compounded by multiantennary, highly sialylated structures if it is conducted by MS [ 34 ]. A recent approach to this task therefore involved enzymatic simplification of N-glycans by sialidase, galactosidase, and fucosidase. Thereby, the original bias toward high-mannose structures was clearly diminished [ 34 ]. MALDI-TOF MS of permethylated glycans circumvents
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Further development and application of a mobile multiple-reflection time-of-flight mass spectrometer for analytical high-resolution tandem mass spectrometry

Further development and application of a mobile multiple-reflection time-of-flight mass spectrometer for analytical high-resolution tandem mass spectrometry

The mass spectrometric analysis of complex volatile and nonvolatile crude oil components falls into the category of such experiments and is one of the most challenging fields in mass spectrometry [Panda et al., 2007]. Crude oil samples are extremely complex and can contain several ten thousand different components. Mass measurements yield dense mass spectra and tens of isobaric constituents at each mass unit. Thus, it is difficult to determine the exact chemical composition of the sample and the use of highly accurate mass spectrometers is vital. If one is interested in the chemical structure of a certain ion species the task becomes even more difficult, since conventional tandem mass spectrometers do not allow for the isolation of molecules from their nearby isobaric contaminants. Hence, fragment spectra always contain product ions of many ion species, which makes the determination of chemical structures very challenging or even impossible. In the following, results of a crude oil measurement with the MR-TOF-MS are presented. The sample was provided by the Max Planck Institute for Coal Re-
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Reverse Sanger-Sequenzierung mittels MALDI-TOF-Massenspektrometrie

Reverse Sanger-Sequenzierung mittels MALDI-TOF-Massenspektrometrie

Für eine erfolgreiche MALDI-TOF Analyse von Fragmentpopulationen aus Sequenzier- reaktionen ist eine schnelle und effiziente Aufreinigung der Reaktionsprodukte von großer Bedeutung. Einen besonderen Stellenwert haben dabei Aufreinigungsverfahren, die auf einer Immobilisierung der Probenmoleküle an eine feste Phase basieren. Sie weisen die für festphasengebundene Reaktionen allgemein bekannten Vorteile wie gute Reproduzier- barkeit, hohes Automatisierungspotenzial, hohe Effizienz und Spezifität etc. auf. Speziell die festphasengestützte Aufreinigung über das Streptavidin-Biotin-System [101] bietet vielfältige Anwendungsmöglichkeiten und konnte bereits zur Aufreinigung von LCR- [78] , PCR- [76,77,102] und Sequenzierprodukten [94] erfolgreich eingesetzt werden. Dieses System zur Isolierung Biotin-markierter DNA besteht aus uniformen superparamagnetischen Polystyrol-Partikeln von 2.8 µm Durchmesser, die über eine kovalente Bindung mit Streptavidin beschichtet sind (im folgenden auch Streptavidin-Beads genannt). Streptavidin ist ein bakterielles, von Streptomyces avidinii gebildetes Protein, das aus vier identischen Untereinheiten aufgebaut ist. Jede Untereinheit trägt eine hochaffine Bindungsstelle für Biotin bzw. Biotin-Konjugate. Obwohl der Streptavidin-Biotin-Komplex durch nicht-kovalente Bindungen gebildet wird, ist die Affinität von Streptavidin zu Biotin etwa um den Faktor eine Million stärker als die der meisten Antigen-Antikörper-Wechselwirkungen (Kd = 10 -15 mol/l). Der Einsatz biotinylierter Templates in enzymatischen Reaktionen erlaubt eine schnelle und effiziente Isolierung der Biotin-markierten Targetmoleküle durch Immobilisierung an die Streptavidin-Dynabeads. Mit einem Magneten können die Streptavidin-beschichteten Partikel an der Gefäßwand zurückgehalten, und so leicht von Puffern, Lösungsmitteln, Enzymen oder unerwünschten Abbauprodukten separiert werden. Zeitaufwendige Methoden zur Isolierung und Reinigung, wie Präzipitation, Extraktion und Zentrifugation werden vermieden. Lässt sich die enzymatische Reaktion, z.B. bei der reversen Sanger Sequenzierung, direkt als Festphasensequenzierung an den Beads durchführen, können zudem Reaktion und anschließende Aufreinigung ohne größeren Substanzverlust in einem Reaktionsgefäß durchgeführt werden. Nach der Aufreinigung an der festen Phase können die Analytmoleküle wieder freigesetzt und massenspektrometrisch detektiert werden.
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Quantitative Investigations on the Diaplacental Transfer of Thallium by Field Desorption Mass Spectrometry 

Quantitative Investigations on the Diaplacental Transfer of Thallium by Field Desorption Mass Spectrometry 

After applying single doses of thallium it was established that a first wave of thallium is swept into the organs very rapidly (1 to 2 h after poi­ soning). This does not apply to the brain, however, which showed a dose dependent barrier for thallium [5]. In the other organs a rapid w ash-out then takes place within the first four hours depending on the function of the kidneys as the first organ o f thallium excretion. This first wave of thallium in the initial period after poisoning is possibly determining for later lethal effects. It is well known that thallium enters the cells in exchange for potassium ions [9] due to their sim ilar ionic radii and same electric charge. One can conclude that the first few h of acute poisoning are decisive for the mechanism of the toxic effects observed.
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Radiolysis Products in Gamma-Irradiated Plastics by Thermal Desorption-Gas Chromatography-Mass Spectrometry

Radiolysis Products in Gamma-Irradiated Plastics by Thermal Desorption-Gas Chromatography-Mass Spectrometry

perimental PP-film; Dr. Wanner and Dr. Sandor Zarka (4P Folie, Forchheim), and Dr. Weiß and Dr. Klerner (BASF AG, Ludwigshafen), who provided the Lupolen and Novolen films; Dr. H.-J. Lengert and Dr. W. Zerweck (Willy Rüsch AG; Waiblingen), who performed an ‘extra’-irradiation; Mrs. Ali Spiegelberg and Dr. Grit Schulzki (BgVV), who shared their lab- oratory facilities and their GC-MS-experience with us; Mr. Werner Blaas Sr. (BgVV) for help and discussions; Dr. Jack Hamilton (The Agriculture and Food Science Centre, Belfast) for an early briefing on MS operation and spectra interpretation; Dr. Andreas Hoffmann (Gerstel GmbH, Mülheim/Ruhr) for TDS- and CIS-operating hints; Dr. Bernd Pfeffer (J & W Scientific) for advice on column selection; Professor Wolfram Schnabel (Hahn-Meitner-Institut, Berlin) for advice and discussions; Mrs. Q. Q. Zhu (HMI), who prepared and irradiated the film samples I used for benzene quantitation; and Professor Walter Jennings (J & W Scientific / Univ. of California, Davis, CA) and Dr. Koni Grob (Kantonales Labor, Zürich, CH), whose seminars on gas chromatography and large-volume injection, respectively, conveyed a sense of how exciting analytical GC can be.
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Determination of Thallium in Brain Tissue by Stable Isotope Dilution and Field Desorption Mass Spectrometry 

Determination of Thallium in Brain Tissue by Stable Isotope Dilution and Field Desorption Mass Spectrometry 

The utility of field desorption mass spectrometry for quantitative metal cation analysis in forensic sciences is demonstrated by the determination of a lethal thallium level in the brain tissue of an experimental anim al. Stable isotope dilution and accumulation of the electrically recorded field desorption ion currents with a multi-channel analyzer allowed a direct estimation of thallium in homogenized tissue samples without further pretreatment. Experim ents with standard solutions revealed the limit of detection for thallium to be about 10 p g of the metal cation.
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Further developments of multi-reflection time-of-flight mass spectrometry and first application for cluster research

Further developments of multi-reflection time-of-flight mass spectrometry and first application for cluster research

2.1 Modes of operation The working principle of any time-of-flight mass spectrometer is illustrated in Fig. 2.3: Due to the velocity difference of ions with different m/q ratios at identical kinetic energies, their separation in time increases with longer total flight times. One of the limiting factors of this, however, is the fact that an ion bunch consisting of only a single species will typically exhibit some distribution of kinetic energies [11]. Its temporal width will thus increase over time, counteracting the growing ToF separation between the different species. The first remediation of this behavior (before the introduction of the MR-ToF principle) was performed by B.A. Mamyrin in 1973 by introducing a “mass-reflectron” capable of folding back ion trajectories [14]. The underlying principle is the fact that ions with higher kinetic energies will penetrate deeper into a reflecting potential barrier, leading to longer flight paths that compensate for their increased velocity in the field-free drift section(s). The time focus, i.e. the point along the trajectory where faster ions catch up with the slower ones, can be tuned to coincide with the system’s detector location after the reflection. The resolving power of the respective ToF mass spectrometer rises from few hundred [13] to several thousand [14] in response.
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Application of electrospray ionization mass spectrometry towards the elucidation of free radical polymerization mechanisms

Application of electrospray ionization mass spectrometry towards the elucidation of free radical polymerization mechanisms

The  present  thesis  investigates  many  facets  of  the  mechanism  of  acrylate  (and  methacrylate)  FRP,  from  the  behavior  of  radical  initiation  processes  induced  by  UV‐ radiation,  to  the  efficient  tuning  of  the  product  spectrum  of  thermally  initiated  n‐butyl  acrylate  polymerization  to  high  conversions  via  the  addition  of  a  transfer  agent,  to  an  investigation  into  the  thiol‐ene  coupling  reaction  to  synthesize  star  polymers  and  an  exploration of the branching characteristics of acrylate FRP polymers. The theme central to  this  thesis  is  the  formation  of  MCRs  as  an  inevitable  side  reaction  in  the  FRP  reaction  mechanism, followed by the reaction pathways which the MCR can subsequently undergo.   The  work  undertaken  herein  aims  to  control  the  fate  of  MCRs  once  they  form,  either  by  exploiting the side reactions which MCRs undergo under certain conditions, or by effectively  repairing and eliminating the MCR once it has formed. Both avenues lead to highly uniform  product  which  requires  no  purification  before  further  reactions  are  possible.  The  macromonomer  product  formed  in  one  case  is  subsequently  employed  in  a  critical  evaluation of the thiol‐ene coupling reaction, with the aim of polymer‐polymer conjugation  to construct star polymer structures. An in‐depth analysis of the product spectrum formed is  conducted  via  ESI‐MS  in  the  thermally  initiated  FRP  of  n‐butyl  acrylate  under  various  conditions of temperature and thiol concentration, demonstrating the versatile tunability of  the  product  spectrum  only  by  controlling  temperature  and  added  thiol  concentration.  A  method for quantitative evaluation of the MS spectra obtained is also introduced.  
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