Investigation on the quantification of pesticides with mass selective detectors

The quantification at trace levels using mass selective detection and internal standards was tested. In a collaborative study the participants determined the concentrations of seven pesticides in an acetone solution and in two spiked potable water extracts. The relative standard deviation ranged from 7 to 20.5%, the average recovery was 101.4%.     

Messung der Wärmeleitfähigkeit von Gasen und Flüssigkeiten nach einem instationären Verfahren

Ohne Zusammenfassung     

The dissociation chemistry of ionized methyl carbamate and its isomers revisited: theory and experiment in concert

Early combined computational and experimental studies by J.K. Terlouw c.s. in Refs. 1-3 propose that low-energy methyl carbamate ions, NH(2)COOCH(3)(?+) (MC-1), rearrange into distonic ions NH(2)C(OH)OCH(2)(?+) and hydrogen-bridged radical cations [NH(2)C=O--H--OCH(2)](?+) (MC-5) en route to the observed losses of HCO(?) and CO. In this study, we report on the generation of ions MC-5 by decarbonylation of ionized methyl oxamate NH(2)COCOOCH(3)(?+). Theory and experiment agree that ion MC-5 is a key intermediate in the dissociation of low-energy ions MC-1. The subsequent HCO(?) loss, however, may not proceed via the route proposed in Ref. 2, but rather by an entirely different mechanism involving proton-transport catalysis (PTC) in ion MC-5. This view is further supported by the dissociation behaviour of the MC-5 isotopologue [ND(2)C=O--D--OCH(2)](?+), which is conveniently generated from the d(3)-labelled glycolamide ion DOCH(2)C(=O)ND(2)(?+).     

Many Familiar Categories can be Interpreted as Categories of Generalized Metric Spaces

The simple concepts of (general) distance function and homometry (a map that preserves distances up to a calibration) are introduced, and it is shown how some natural distance functions on various mathematical objects lead to concrete embeddings of the following categories into the resulting category DIST°: quasi-pseudo-metric, topological, and (quasi-)uniform spaces with various kinds of maps; groups and lattice-ordered abelian groups; rings and modules, particularly fields; sets with reflexive relations and relation-preserving maps (particularly directed loop-less graphs and quasi-ordered sets); measured spaces with Radon-continuous maps; Boolean, Brouwerian, and orthomodular lattices; categories with combined objects, for example topological groups, ordered topological spaces, ordered fields, Banach spaces with linear contractions or linear continuous maps and so on.     

Bestimmung von isomeren 4-Nonylphenolen in B?den

Summary It was reported that 4-nonylphenol isomers had been found in high concentrations in sewage sludge. When this sludge is applied to fields there is a risk that soils may be contaminated with nonylphenols. Therefore, a method is described here for the determination of 4-nonylphenol isomers in soil. The steam distillation/solvent extraction technique is used. An essential part of the method is the clean-up step by column chromatography. The determination is performed on a fused silica capillary by a flame ionization or a mass selective detector. Average recoveries from soil samples spiked with 0.1 to 1 mg/kg ranged from 90 to 116%. The detection limit is 0.1–0.05 mg/kg soil (this limit corresponds to the technical mixture of the isomers).     

Nontargeted Screening Using Gas Chromatography–Atmospheric Pressure Ionization Mass Spectrometry: Recent Trends and Emerging Potential

Gas chromatography–high-resolution mass spectrometry (GC–HRMS) is a powerful nontargeted screening technique that promises to accelerate the identification of environmental pollutants. Currently, most GC–HRMS instruments are equipped with electron ionization (EI), but atmospheric pressure ionization (API) ion sources have attracted renewed interest because: (i) collisional cooling at atmospheric pressure minimizes fragmentation, resulting in an increased yield of molecular ions for elemental composition determination and improved detection limits; (ii) a wide range of sophisticated tandem (ion mobility) mass spectrometers can be easily adapted for operation with GC–API; and (iii) the conditions of an atmospheric pressure ion source can promote structure diagnostic ion–molecule reactions that are otherwise difficult to perform using conventional GC–MS instrumentation. This literature review addresses the merits of GC–API for nontargeted screening while summarizing recent applications using various GC–API techniques. One perceived drawback of GC–API is the paucity of spectral libraries that can be used to guide structure elucidation. Herein, novel data acquisition, deconvolution and spectral prediction tools will be reviewed. With continued development, it is anticipated that API may eventually supplant EI as the de facto GC–MS ion source used to identify unknowns.     

The geometry of chaotic dynamics — a complex network perspective

Recently, several complex network approaches to time series analysis have been developed and applied to study a wide range of model systems as well as real-world data, e.g., geophysical or financial time series. Among these techniques, recurrence-based concepts and prominently ε-recurrence networks, most faithfully represent the geometrical fine structure of the attractors underlying chaotic (and less interestingly non-chaotic) time series. In this paper we demonstrate that the well known graph theoretical properties local clustering coefficient and global (network) transitivity can meaningfully be exploited to define two new local and two new global measures of dimension in phase space: local upper and lower clustering dimension as well as global upper and lower transitivity dimension. Rigorous analytical as well as numerical results for self-similar sets and simple chaotic model systems suggest that these measures are well-behaved in most non-pathological situations and that they can be estimated reasonably well using ε-recurrence networks constructed from relatively short time series. Moreover, we study the relationship between clustering and transitivity dimensions on the one hand, and traditional measures like pointwise dimension or local Lyapunov dimension on the other hand. We also provide further evidence that the local clustering coefficients, or equivalently the local clustering dimensions, are useful for identifying unstable periodic orbits and other dynamically invariant objects from time series. Our results demonstrate that ε-recurrence networks exhibit an important link between dynamical systems and graph theory.     

On the interaction of peptides with calcium ions as studied by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry: towards peptide fishing using metal ion baits

In a previous report [J.W. de Beukelaar, J.W. Gratama, P.A. Sillevis Smitt, G.M. Verjans, J. Kraan, Th.M. Luider, P.C. Burgers, Rapid Commun. Mass Spectrom. 21 (2007) 1282] on the quality assessment of synthetic peptides used in protein-spanning peptide pools by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) we noted that certain peptides showed remarkably intense signals for their calcium-containing analogues. Here we report on a detailed mass spectrometric study of the unimolecular chemistry of these calcium-containing peptides. By integration of the experimental findings with computational results derived from DFT and the CBS-QB3 model chemistry, we have traced the processes induced by Ca²⁺ attachment in the peptide ions.Key to our analysis is the observation that all of the studied calcium-bound peptides containing a threonine or serine residue show prominent losses of CH₃CHO (from threonine) and/or CH₂O (from serine) in both the positive and the negative ion mode. In the first step, Ca²⁺ attaches itself to a negatively charged in-chain carboxylate group. Next, electrophilic attack of the calcium ion on the CH(R)OH group of threonine (RCH₃) or serine (RH) releases the hydroxyl proton which can then move to a suitable acceptor site, viz. a peptide bond. This leads to the formation of a very stable ionic bidentate structure. Upon collisional activation (MS/MS), this bidentate opens up leading to the loss of the exposed acetaldehyde or formaldehyde molecule, to yield another bidentate structure.MS/MS spectra of selected peptides interacting with other metal ions have also been investigated and it is found that only divalent ions follow the Ca²⁺-induced transformations.