Analysis of trace levels of pesticides in rainwater by SPME and GC-tandem mass spectrometry after derivatisation with PFFBr

Solid-phase microextraction (SPME) was used for the analysis of some pesticides (bromoxynil, chlorotoluron, diuron, isoproturon, 2,4-MCPA, MCPP and 2,4-D) in rainwater after derivatisation with PFBBr and gas chromatography-ion trap mass spectrometry. The derivatisation procedure was optimized by testing different methods: direct derivatisation in the aqueous phase followed by SPME extraction, on-fibre derivatisation and derivatisation in the injector. The best result was obtained by headspace coating the PDMS/DVB fibre with PFBBr for 10 min followed by direct SPME extraction for 60 min at 68 °C (pH 2 and 75% NaCl). Good detection limits were obtained for all the compounds: these ranged between 10 and 1,000 ng L⁻¹ with a relatively high uncertainty due to the combination of derivatisation and SPME extraction steps. The optimized procedure was applied to the analysis of pesticides in rainwater and results obtained shows that this method is a fast and simple technique to assess the spatial and temporal variations of concentrations of pesticides in rainwater.     

Separation of molecular tracers sorbed onto atmospheric particulate matter by flash chromatography

In to order increase sensitivity and to reduce the background induced by matrix effects, a method was developed that uses flash chromatography to separate various compounds present in atmospheric aerosol samples prior to their analysis with different analytical techniques (GC–MS, GC–FID, HPLC). For this purpose, flash chromatography using a 4 g silica gel column crossed by eluent at a flow rate of 20 mL min⁻¹ was used. An eluent with enhanced polarity is needed to separate nonpolar (linear and branched alkanes), semipolar (PAH, nitro-PAH and cholesterol) and polar (methoxyphenols, alkanoic acids, and levoglucosan) compounds. Three combinations of solvents were used: hexane for the nonpolar fraction (F1), toluene/hexane for the semipolar fraction (F2) and dimethylformamide for the polar fraction (F3). The use of different eluents for each fraction allows separation of the sample to be accomplished with good repeatability and satisfying yields [85 ± 5% for F1, 81 ± 8% (PAHs), 89 ± 6% (nitro-PAHs) and 74 ± 7% (cholesterol) for F2 and 79 ± 7% (n-alkanoic acids), 40 ± 11% (methoxyphenols) and 77 ± 6% (levoglucosan) for F3]. The methoxyphenol yields were low due to losses during the concentration/evaporation step. This method was then applied to analyse the organic composition of particles collected at an urban site in Strasbourg (France).     

Slice imaging of the quantum state-to-state cross section for photodissociation of state-selected rovibrational bending states of OCS (v2=0,1,2/JlM)+hnu-->CO(J)+S(1D2)

Using hexapole quantum state-selection of OCS (v(2)=0,1,2/JlM) and high-resolution slice imaging of quantum state-selected CO(J), the state-to-state cross section OCS (v(2)=0,1,2/JlM)+hnu-->CO(J)+S((1)D(2)) was measured for bending states up to v(2)=2. The population density of the state-selected OCS (v(2)=0,1,2 /JlM) in the molecular beam was obtained by resonantly enhanced multiphoton ionization of OCS and comparison with room temperature bulk gas. A strong increase of the cross section with increasing bending state is observed for CO(J) in the high J region, J=60-67. Integrating over all J states the authors find sigma(v(2)=0):sigma(v(2)=1):sigma(v(2)=2)=1.0:7.0:15.0. A quantitative comparison is made with the dependence of the transition dipole moment function on the bending angle.     

Comprehensive multi-residue method for the target analysis of pesticides in crops using liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS) multi-residue method for the simultaneous target analysis of a wide range of pesticides and metabolites in fruit, vegetables and cereals has been developed. Gradient elution has been used in conjunction with positive mode electrospray ionization tandem mass spectrometry to detect up to 171 pesticides and/or metabolites in different crop matrices using a single chromatographic run. Pesticide residues were extracted/partitioned from the samples with acetone/dichloromethane/light petroleum. The analytical performance was demonstrated by the analysis of extracts from lettuce, orange, apple, cabbage, grape and wheat flour, spiked at three concentration levels ranging from 0.01 to 0.10 mg/kg for each pesticide and/or metabolite. In general, recoveries ranging from 70 to 110%, with relative standard deviations better than 15%, were obtained. The recovery and repeatability data are in good accordance with EU guidelines for pesticide residue analysis. The limit of quantification for all targeted pesticides and metabolites tested was 0.01 mg/kg. The selectivity and robustness of the LC-MS/MS method was demonstrated by a 1-year comparison of its analytical results with those obtained from our validated GC and LC multi-residue methods applied to more than 3500 routine samples. The validated LC-MS/MS method has been implemented in our analytical scheme since 2004, replacing four of the conventional detection methods, i.e. GC-flame-photometric detection (acephate, methamidophos, etc.), GC-nitrogen-phosphorus detection, LC-UV detection (carbendazim, thiabendazole, imazalil and prochloraz) and LC-fluorescence detection (N-methylcarbamate pesticides). During a 3-year period, the LC-MS/MS method has been applied to the analyses of more than 12,000 samples.     

Surface modification of chlorobutyl rubber by plasma polymerization

Radio frequency (r.f.) plasma polymerization of vinylidene fluoride (CH₂CF₂) has been used to modify the surface properties of chlorobutyl rubber. FTIR-ATR spectra of the treated rubbers and transmission spectra of plasma polymer films on NaCl windows indicated that as power increased the F/H ratio decreased. SIMS tests supported the FTIR results, and showed that the decrease in the F/H ratio was due to a decrease in the amount of F and an increase in the amount of H in the plasma polymer. Sliding friction measurements showed a reduction in the coefficient of friction (μ) from 3.7 for the untreated rubber to values ranging between 0.4 and 1.9 for the plasma-treated rubbers. There did not appear to be any correlation between the coefficient of friction and plasma power or monomer flow rate, and the average coefficient of friction for the plasma-treated samples was 0.9, which was lower than a commercially used silicone oil treatment (μ = 1.1–1.3). Repetitive sliding friction tests showed that the plasma- and silicone oil treated-chlorobutyl rubbers had the similar lubricating lifetimes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1651–1660, 1997     

Dramatically Enhanced Fluorescence of Heteroaromatic Chromophores upon Insertion as Spacers into Oligo(triacetylene)s

In continuation of a previous study on the modulation of π‐electron conjugation of oligo(triacetylene)s by insertion of central hetero‐spacer fragments between two (E)‐hex‐3‐ene‐1,5‐diyne ((E)‐1,2‐diethynylethene, DEE) moieties (Fig. 1), a new series of trimeric hybrid oligomers ( 14 – 18 and 22 – 24 , Fig. 2) were prepared (Schemes 1–3). Spacers used were both electron‐deficient (quinoxaline‐based heterocycles, pyridazine) and electron‐rich (2,2′‐bithiophene, 9,9‐dioctyl‐9H‐fluorene) chromophores. With 19–21 (Scheme 4), a series of transition metal complexes was synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramolecular assembly. The UV/VIS spectra (Fig. 3) revealed that the majority of spacers provided hetero‐trimers featuring extended π‐electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer 13 and homo‐trimer 12 (Fig. 5). This increase in emission intensity appears as a general feature of these systems: even if the spacer molecule is non‐fluorescent, the corresponding hetero‐trimer may show a strong emission (Table 2). The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating‐disk voltammetry (RDV) (Table 3 and Fig. 5). In each case, the first one‐electron reduction step in the hetero‐trimers appeared anodically shifted compared with DEE dimer 13 and homo‐trimer 12 . With larger spacer chromophore extending into two dimensions (as in 14 – 18 , Fig. 2), the anodic shift (by 240–490 mV, Table 3) seems to originate from inductive effects of the two strongly electron‐accepting DEE substituents rather than from extended π‐electron conjugation along the oligomeric backbone, as had previously been observed for DEE‐substituted porphyrins.     

Mesoscopic Fluctuations for the Thinned Circular Unitary Ensemble

In this paper we study the asymptotic behavior of mesoscopic fluctuations for the thinned Circular Unitary Ensemble. The effect of thinning is that the eigenvalues start to decorrelate. The decorrelation is stronger on the larger scales than on the smaller scales. We investigate this behavior by studying mesoscopic linear statistics. There are two regimes depending on the scale parameter and the thinning parameter. In one regime we obtain a CLT of a classical type and in the other regime we retrieve the CLT for CUE. The two regimes are separated by a critical line. On the critical line the limiting fluctuations are no longer Gaussian, but described by infinitely divisible laws. We argue that this transition phenomenon is universal by showing that the same transition and their laws appear for fluctuations of the thinned sine process in a growing box. The proofs are based on a Riemann-Hilbert problem for integrable operators.     

Bump time-frequency toolbox: a toolbox for time-frequency oscillatory bursts extraction in electrophysiological signals

Background  

oscillatory activity, which can be separated in background and oscillatory burst pattern activities, is supposed to be representative of local synchronies of neural assemblies. Oscillatory burst events should consequently play a specific functional role, distinct from background EEG activity – especially for cognitive tasks (e.g. working memory tasks), binding mechanisms and perceptual dynamics (e.g. visual binding), or in clinical contexts (e.g. effects of brain disorders). However extracting oscillatory events in single trials, with a reliable and consistent method, is not a simple task.     

The Symplectic Camel and the Uncertainty Principle: The Tip of an Iceberg?

We show that the strong form of Heisenberg’s inequalities due to Robertson and Schrödinger can be formally derived using only classical considerations. This is achieved using a statistical tool known as the “minimum volume ellipsoid” together with the notion of symplectic capacity, which we view as a topological measure of uncertainty invariant under Hamiltonian dynamics. This invariant provides a right measurement tool to define what “quantum scale” is. We take the opportunity to discuss the principle of the symplectic camel, which is at the origin of the definition of symplectic capacities, and which provides an interesting link between classical and quantum physics.     

para‐Sulfonated Calixarenes Used as Synthetic Receptors for Complexing Photolabile Cholinergic Ligand

The water‐soluble tetra‐, hexa‐ and octasulfonated calix[4]arenes, calix[6]arenes, and calix[8]arenes 1 – 3 , respectively, were investigated as potential synthetic receptors for photolabile cholinergic ligand A , a photolytic precursor of choline. Ligand A is a bifunctional molecule carrying a photolabile 2‐nitrobenzyl group at one end and a choline moiety at the other end. Results from NMR studies have shown that calixarenes 1 – 3 form stable 1 : 1 complexes with A , having similar binding potential to that observed with the cholinergic enzymes acetylcholinesterase and butyrylcholinesterase. Further studies have suggested that calix[8]arene forms a ditopic complex by binding concomitantly to both the cationic choline moiety and the aromatic photolabile group of A , whereas calix[4]arene and calix[6]arene form monotopic complexes with A . The ditopic complex between calix[8]arene and A results from mutually induced fitting process, while the monotopic complexes between calix[4]arene and A can be regulated by pH: at neutral pH, calix[4]arene specifically binds the cationic choline moiety, while, at acidic pH, it complexes unselectively both the cationic choline moiety and the aromatic group of A . Our results show that para‐sulfonated calixarenes are versatile artificial receptors which bind in various ways to the bifunctional photolabile cholinergic ligand A , depending on their size, geometry, and state of protonation.