Fast,high-sensitivity,multipesticide analysis of complex mixtures with supersonic gas chromatography-mass spectrometry

We developed a new instrumental approach, termed Supersonic GC-MS, which achieves fast, sensitive, confirmatory and quantitative analysis of a broad range of pesticides in complex agricultural matrices. Our Supersonic GC-MS system is a modification of a bench-top Agilent 6890 GC+5972 MSD with a supersonic molecular beam (SMB) interface and fly-through EI ion source. One of the main advantages of Supersonic GC-MS is an enhanced molecular ion (M+) in the resulting mass spectra. For example, the M+ was observed in all 88 pesticides that we studied using the Supersonic GC-MS whereas only 36 of 63 (57%) pesticides that we investigated in standard GC-MS exhibited a M+. We also found that the degree of matrix interference is exponentially reduced with the fragment mass by about 20-fold per 100 amu increasing mass. The enhancement of the M+ combined with the reduction in matrix background noise permit rapid full scan analysis of a potentially unlimited number of pesticides, unlike selected ion monitoring or MS-MS in which specific conditions are required in segments for targeted pesticides. Furthermore, unlike the case with chemical ionization, EI-SMB-MS spectra still give accurate identification of compounds using common mass spectral libraries. In practice,we found thatlibraries favor mass spectra in which the M+ appears, thus Supersonic GC-MS produced better spectra for compound identification than standard GC-MS. To achieve even lower identification limits, the M+ plus a second major ion (still using full scan data) gives higher signal-to-chemical noise ratios than the traditional 3-ion approach. The replacement of two low-mass ions with the M+ (supersonic two-ions method) results in a significant reduction of matrix interference by a factor of up to 90. Another main advantage of Supersonic GC-MS is its exceptional suitability for fast GC-MS with high carrier gas flow-rate. Fast Supersonic GC-MS was able to analyze thermally labile pesticides, such as carbamates, that are difficult or impossible to analyze in standard GC-MS. Large volume injection using a ChromatoProbe was also demonstrated, in the 6 min analysis of pesticides at 20 ng/g in a spice matrix.     

High-efficiency surface-induced dissociation on a rhenium oxide surface

We report on the high-efficiency surface-induced dissociation of benzene and cyclohexane polyatomic ions after scattering from a rhenium oxide surface with a kinetic energy of 5–290 eV. Rhenium oxide was prepared by directly heating a rhenium metal foil, under 10^?5 mbar partial oxygen pressure, at about 1000 K. Rhenium oxide is characterized by a very high work function of 6.4 eV and thus minimizes ion reneutralization probabilities. The catalytic combustion of surface organic impurities with oxygen ensures good long-term stability. We found that the surface-induced dissociation ion current is 70 times larger on rhenium oxide than on bare rhenium or stainless steel. Absolute scattered ion yields of about 50% were measured. The implications of surface-induced dissociation on mass spectrometry in supersonic molecular beams are mentioned.     

Preparation and Fungitoxicity of Some Dibromo-8-quinolinols

Summary.  2,5-, 3,5-, 3,6-, 3,7-, 4,5-, 5,6-, 5,7-, and 6,7-dibromo-8-quinolinols were prepared and tested against six fungi (Aspergillus niger, Aspergillus oryzae, Myrothecium verrucaria, Trichoderma viride, Mucor cirinelloides, and Trichophyton mentagrophytes) in Sabouraud dextrose broth. Most of the compounds were strongly antifungal, inhibiting five of the fungi below 1μg/cm³, but were somewhat less fungitoxic than the corresponding chloro analogues. M. cirinelloides was not inhibited by any of the compounds except 4,5-dibromo-8-quinolinol. This high level of fungitoxicity is attributed to intramolecular synergism. Received December 28, 2000. Accepted (revised) February 3, 2001     

Resonance trapping in dissipative and antidissipative systems: An ergodic approach

We propose a weak definition for a resonance trapping in oscillating systems. This definition requires the convergence of orbits, in the sense of measures convergence, to ah ergodic invariant measure, supported in a small neighborhood of the resonance zone. Then we apply this definition to a simplified, single-frequency oscillating system which admits a finite number of resonance points. It turns out that, under some assumptions, this generalized concept of resonance trapping may include the case where all resonances are repelling in the classical sense. The analysis is reduced to the investigation of the integrability of the logarithmic singularity with respect to an invariant measure of a reduced mapping.     

Observation of B-/+-->rho-/+rho0 decays

We report the first observation of the charmless vector-vector decay process B-/+-->rho(-/+)rho(0). The measurement uses a 78 fb(-1) data sample collected with the Belle detector at the KEKB asymmetric e(+)e(-) collider operating at the Upsilon(4S) resonance. We obtain a branching fraction of B(B-/+-->rho(-/+)rho(0))=[31.7+/-7.1(stat)+3.8-6.7(syst)]x10(-6). An analysis of the rho helicity-angle distributions gives a longitudinal polarization fraction of Gamma(L)/Gamma=0.95+/-0.11(stat)+/-0.02(syst). We also measure the direct-CP-violating asymmetry A(CP)(B-/+-->rho(-/+)rho(0))=0.00+/-0.22(stat)+/-0.03(syst).     

Observation of B0-->pLambda(pi)(-)

We report the first observation of the charmless hyperonic B decay, B0-->pLambda(pi)(-), using a 78 fb(-1) data sample recorded on the Upsilon(4S) resonance with the Belle detector at KEKB. The measured branching fraction is B(B0-->pLambda(pi)(-))=(3.97(+1.00)(-0.80)+/-0.56)x10(-6). Searches for B0-->pLambda(K)- and pSigma(0)pi(-) yield no significant signals and we set 90% confidence-level upper limits of B(B0-->pLambda(K)-)<8.2x10(-7) and B(B0-->pSigma(0)pi(-))<3.8x10(-6).     

Measurements of B decays to two kaons

We report measurements of B meson decays to two kaons using 253 fb(-1) of data collected with the Belle detector at the KEKB energy-asymmetric e+ e- collider. We find evidence for signals in B+ --> K0 K+ and B0 --> K0 K0 with significances of 3.0sigma and 3.5sigma, respectively. (Charge-conjugate modes are included.) The corresponding branching fractions are measured to be [symbol: see text](B+ --> K0 K+) = (1.0 +/- 0.4 +/- 0.1) x 10(-6) and [symbol: see text](B0 --> K0 K0) = (0.8 +/- 0.3 +/- 0.1) x 10(-6). These decay modes are examples of hadronic bd transitions. No signal is observed in the decay B0 --> K+ K-, and we set an upper limit of 3.7 x 10(-7) at 90% confidence level.     

Translational entanglement via collisions: how much quantum information is obtainable?

We study collisions mediated by finite-range potentials as a tool for generating translational entanglement between unbound particles or multipartite systems. The general analysis is applied to one-dimensional scattering, where resonances and the initial phase-space distribution are shown to determine the degree of postcollisional entanglement.     

Vibrations and buckling of axially loaded stiffened cylindrical shells with elastic restraints

A theory is derived for calculation of the influence of elastic edge restraints on the vibrations and buckling of stiffened cylindrical shells. The stiffeners are considered “smeared” and the edge restraints can be axial, radial, circumferential or rotational. Extensive computations are performed for special kinds of stringer-stiffened shells, and the theoretical predictions are compared with experimental results. A method of definition of equivalent elastically restrained boundary conditions by use of vibration tests is discussed. Application of this technique to tests on 10 shells significantly reduces the scatter in the ratio of experimental to predicted buckling loads.     

The first general method for alpha-trifluoromethylation of carboxylic acids using BrF3

2-Carbomethoxy-1,1-bis(methylsulfide)-1-alkenes, easily made from carboxylic acids, CS(2) and MeI, were treated with BrF(3) producing eventually the desired alpha-trifluoromethyl carboxylate derivatives--RCH(CF(3))COOR'--in good yields.