Interlaboratory determinations of isotopically enriched metals by field desorption mass spectrometry

Summary The isotopic distribution of stable isotopes in six enriched metals (calcium, copper, barium, rubidium, strontium and thallium) has been determined by field desorption mass spectrometry. A first evaluation of the interlaboratory reproducibility of the application of this method for trace determination of metals was made using three different types of mass spectrometers in three different laboratories. The standard deviations for the most abundant isotopes of the metals investigated are between +-0.1 and +-0.5%. Within these standard deviations, the values obtained by the three mass spectrometry groups are the same. To support the accuracy of our quantification, thermal ionization mass spectrometry has been employed and confirms the results of the field desorption method.

---

Ringversuche zur Bestimmung des Anreicherungsgrades von Stabilisotopen in Metallen mit Felddesorptions-Massenspektrometrie

Zusammenfassung Die Isotopenverteilung von stabilen Isotopen in sechs angereicherten Metallen (Calcium, Kupfer, Barium, Rubidium, Strontium und Thallium) wurde mit der Felddesorptions-Massenspektrometrie quantitativ bestimmt. Drei verschiedene Typen von Massenspektrometern in drei verschiedenen Laboratorien wurden für diese Untersuchungen benutzt und es ergab sich eine erste Wertung für die Reproduzierbarkeit dieses Verfahrens bei der Spurenbestimmung von Metallen. Die Standardabweichungen für das jeweils häufigste Isotop der untersuchten Metalle lag zwischen +-0.1 und +-0.5 %. Die quantitativen Resultate der drei massenspektrometrischen Arbeitsgruppen stimmten gut überein und lagen alle innerhalb dieses Bereichs der Standardabweichung. Um die Richtigkeit dieser Quantifizierung abzustützen, wurden die Proben der angereicherten Metalle ebenfalls mit der Thermionisations-Massenspektrometrie gemessen. Dieses zweite, unabhängige Verfahren bestätigt eindeutig die Ergebnisse der Felddesorptions-Massenspektrometrie.

---

---

Quantitative Field Desorption Mass Spectrometry, Part XXVII; for part XXVI see ref. [20]     

Analysis of biopolymers by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry is an analytical technique enabling the mass analysis of biopolymers with masses up to at least 300,000 Da. Incorporation of analyte in a matrix consisting of small highly absorbing organic molecules and excitation with short pulses of intense laser light enables the production of intact molecule ions to be analyzed in a time-of-flight mass spectrometer. Mass accuracies of up to 0.01% can be achieved from sample amounts of 1 pmol or less. Proteins, glycoproteins, oligonucleotides and oligosaccharides have been analyzed. The short analysis time of several minutes makes the method well suited for combination with other biochemical methods.     

Determination of lithium traces in microliters of water,wine and high purity solvents by stable isotope dilution and field desorption mass spectrometry

Summary In this work, the applicability of field desorption mass spectrometry for the determination of lithium in mineral and tap water, wine and high-purity solvents has been examined. Because of the outstanding sensitivity of field desorption mass spectrometry for alkali cations and the high specificity of mass spectrometry, it was possible to determine lithium from microlitre samples by using the method of stable isotope dilution. Lithium, at levels of 10^–7–10^–4 mg/ ml, was determined in the samples without any pretreatment. The time required for one analysis was about 20–30 min. The results from quantitative analyses of mineral water were compared with others obtained by atomic-absorption spectrophotometry and were in good agreement. The very small concentrations of lithium in wine and high-purity solvents, which are too low to be measured by conventional atomic-absorption techniques, can be determined accurately without difficulty by field desorption mass spectrometry.

---

Zusammenfassung Die Anwendung der Felddesorptions-Massenspektrometrie für die Bestimmung von Lithium in Mineral- und Leitungswasser, Wein und hochreinen Lösungsmitteln wurde beschrieben. Wegen der außerordentlich hohen Empfindlichkeit dieses Verfahrens für Alkali-Kationen und der hohen Spezifität des massenspektrometrischen Nachweises war es möglich, Lithium aus Mikroliter-Proben mit Hilfe der Isotopen-Verdünnungs-Analyse zu bestimmen. Lithium wurde ohne jede Probenvorbehandlung in Konzentrationen von ungefähr 10^–7–10^–4 g/l bestimmt. Die Zeit pro Analyse betrug ungefähr 20–30 Minuten. Die Ergebnisse dieser quantitativen Messungen in Mineralwasser wurden mit denen der Atomabsorptions-Spektroskopie verglichen und befinden sich in guter Übereinstimmung. Die sehr kleinen Konzentrationen von Lithium in Wein und hochreinen Lösungsmitteln sind für die Messung mit konventioneller Atomabsorptions-Spektroskopie zu gering, können aber ohne Schwierigkeiten und mit guter Genauigkeit mit der Felddesorptions-Massenspektrometrie bestimmt werden.

---

---

Quantitative Field Desorption Mass Spectrometry: Part XII, for part XIII see Ref. 16.     

Analysis of heterogeneous deformation and dislocation dynamics in single crystal micropillars under compression

The size dependent deformation of Cu single crystal micropillars with thickness ranging from 0.2 to 2.5 μm subjected to uniaxial compression is investigated using a Multi-scale Dislocation Dynamics Plasticity (MDDP) approach. MDDP is a hybrid elasto-viscoplastic simulation model which couples discrete dislocation dynamics at the micro-scale (software micro3d) with the macroscopic plastic deformation. Our results show that the deformation field in these micropillars is heterogeneous from the onset of plastic flow and is confined to few deformation bands, leading to the formation of ledges and stress concentrations at the surface of the specimen. Furthermore, the simulation yields a serrated stress–strain behavior consisting of discrete strain bursts that correlates well with experimental observations. The intermittent operation and stagnation of discrete dislocation arms is identified as the prominent mechanism that causes heterogeneous deformation and results in the observed macroscopic strain bursts. We show that the critical stress to bow an average maximum dislocation arm, whose length changes during deformation due to pinning events, is responsible for the observed size dependent response of the single crystals. We also reveal that hardening rates, similar to that shown experimentally, occur under relatively constant dislocation densities and are linked to dislocation stagnation due to the formation of entangled dislocation configuration and pinning sites.     

Nano-electrospray ionization mass spectrometry: addressing analytical problems beyond routine

The advent of nano-electrospray ionization (nano-ESI) has considerably extended the usability of ESI in the analytical mass spectrometric laboratory. One of the remarkable features of nano-ESI is its extremely low sample consumption. Only a few microliters of analyte solution (10^–5–10^–8 M) are sufficient for molecular weight determination and structural investigations by MS/MS. But nano-ESI is more than just a minimized-flow ESI; the low solvent flow rate also affects the mechanism of ion formation. As a consequence, the area of ESI-MS applications is significantly enhanced. Oligosaccharides, glycosides as well as glycoproteins can be analyzed more easily than with normal ion spray. The same holds for the analysis of non-covalent complexes sprayed directly from aqueous solutions.     

Catalytic Antibodies by Fluorescence Screening

A series of eleven immunizations against transition-state analogs were carried out to improve the catalytic properties of Ab 9D9, a catalytic antibody that catalyzes a fluorogenic retro-Diels-Alder reaction liberating nitroxyl. By a direct fluorescence assay of cell-culture supernatant, eight new hybridoma cell lines producing catalytic antibodies for the reaction were readily identified among more than 14000 individual samples. Our results demonstrate that early catalysis screening by fluorescence allows an efficient survey of large antibody libraries, and may lead to rapid and significant improvement in catalysis.     

Fire retardancy effects in single and double layered sol–gel derived TiO2 and SiO2-wood composites

Sol–gel derived TiO₂ and SiO₂-wood inorganic composites are prepared by direct vacuum infiltration of silicon and titanium alkoxide based precursors in pine sapwood in one or two cycles followed by a controlled thermal curing process. The resulting flame retardancy effect is investigated under two different fire scenarios using cone calorimetry and oxygen index (LOI). Heat release rates (HRR) especially the values for the second peak, are reduced moderately for all single layered composites. This effect is more pronounced for double layered composites where HRR was reduced up to 40 % showing flame retardancy potential in developing fires. Beside this, smoke release was lowered up to 72 % indicating that these systems had less fire hazards compared to untreated wood, whereas no meaningful improvement is realized in terms of fire load (total heat evolved) and initial HRR increase. However impressively, the LOI of the composites were increased up to 41 vol% in comparison to 23 vol% for untreated wood displaying a remarkable flame retardancy against reaction to a small flame. An approximate linear interdependence among the fire properties and the material loading as well as fire residue was observed. A residual protection layer mechanism is proposed improving the residue properties for the investigated composites.