Cross sections for energetic heavy-ion impact on protonated water clusters

Energetic impact of multiple ionized oxygen on protonated water clusters in the range of eight to twenty-one water molecules is investigated on the ZERNIKE--LEIF facility. The target water clusters are stored in a Paul trap and thermalized by cold buffer gas. This well-controlled approach allows for a direct measurement of the total inelastic cross section leading to trap-loss processes of the target ions.     

A Monte Carlo evaluation of three methods to detect local dependence in binary data latent class models

Binary data latent class analysis is a form of model-based clustering applied in a wide range of fields. A central assumption of this model is that of conditional independence of responses given latent class membership, often referred to as the “local independence” assumption. The results of latent class analysis may be severely biased when this crucial assumption is violated; investigating the degree to which bivariate relationships between observed variables fit this hypothesis therefore provides vital information. This article evaluates three methods of doing so. The first is the commonly applied method of referring the so-called “bivariate residuals” to a Chi-square distribution. We also introduce two alternative methods that are novel to the investigation of local dependence in latent class analysis: bootstrapping the bivariate residuals, and the asymptotic score test or “modification index”. Our Monte Carlo simulation indicates that the latter two methods perform adequately, while the first method does not perform as intended.     

Inside Cover: A Synthetic Lectin for O‐Linked β‐N‐Acetylglucosamine (Angew. Chem. Int. Ed. 10/2009)

Carbohydrates are slippery customers in water. Camouflaged by solvent‐mimicking hydroxy groups, they make challenging targets, even for natural receptors. In their Communication on page 1775 ff., A. P. Davis and co‐workers describe a synthetic receptor that is remarkably effective for the important β‐N‐acetylglucosaminyl (β‐GlcNAC) unit. The affinities of the receptor are good and its selectivities are excellent, even by the standards of natural carbohydrate‐binding proteins.

     

Ammonium perfluorooctanoate as a volatile surfactant for the analysis of N-methylcarbamates by MEKC-ESI-MS

Ammonium perfluorooctanoate (APFOA) was investigated as an MS-friendly surfactant for the analysis of a mixture of ten N-methylcarbamates with MEKC-ESI-MS. Because of the relatively low boiling point of perfluorooctanoic acid ( approximately 190 degrees C), APFOA can be introduced into a mass spectrometer without the adverse effects of less volatile surfactants such as SDS. With a BGE consisting of 50 mM APFOA/isopropanol (IPA) 98:2 and with 30 kV applied, a very fast separation ( approximately 6 min) was possible with only one pair of analytes comigrating. Using an experimental design with four factors (voltage, nebulizer pressure, concentration of APFOA, and concentration of IPA) we were able to resolve all analytes in just over 11 min. Sheath liquid composition and flow rate, drying gas temperature and flow rate, and fragmentor voltage were then optimized for maximum signal intensity and S/N. It was found that the faster method gave better S/N because of narrower peak widths, and detection limits in SIM mode were between 0.01 (aldicarb) and 0.08 mg/L (methomyl). Calibration curves were prepared with standards of 0.50, 1.00, and 2.00 mg/L for the analysis of samples obtained after SPE of tap water spiked with the ten N-methylcarbamates at a level of 10 microg/L. All analytes showed very good recoveries (>86%), except for the most polar analyte aldicarb sulfone (recovery of 73%), testifying for the potential use of APFOA for this kind of analyses.     

Plane-wave calculations applied to conjugated polymers

Density functional calculations using pseudopotentials and a plane-wave basis set are applied to study the geometry and the electronic structure of conjugated polymers consisting of heterocyclic aromatic rings. This article focuses on the computational methods. The influence of the pseudopotentials on the structural and electronic properties is studied. The rates of convergence of these properties with respect to the basis set size and the density of sampling points for the Brillouin zone integration are considered. The effects of using different exchange–correlation potentials (local density or generalized gradient approximations) are examined. It is shown that smooth norm-conserving pseudopotentials used for calculations on conjugated polymers lead to converged results with a moderately sized basis set. Received: 20 August 1999 / Accepted: 23 November 1999 / Published online: 19 April 2000     

Intercomparison on measurements of PCBs in pork fat during the Belgian PCB-crisis

During the Belgian PCB crisis (1999/2000) the quality of the data from the PCB monitoring were studied with a proficiency testing experiment. Pork fat that was spiked at the Institute for Reference Materials and Measurements (EC-JRC-IRMM) was sent out as unknown to all laboratories that participated in the monitoring. In parallel, the material was certified on the basis of the results of several leading PCB laboratories throughout Europe that did not participate in the monitoring. During the first round 15 to 25% deviation was experienced, while in the end of this multistep intercalibration procedure the average deviation for the respective PCBs was 10.9% (PCB 28), 13.1% (PCB 52), 10.1% (PCB 101), 10.7% (PCB 118), 10.7% (PCB 138), 9.1% (PCB 153), 8.1% (PCB 180) and 8.2% for the sum of the 7 PCBs. The concentrations measured for the higher volatile PCB 28 had a tendency to show lower levels, while for PCB 180 this was less pronounced. On the other hand, PCB 153 showed results rather to the higher side. During this exercise the material was also tested for stability by one of the certifying laboratories.     

Diffusion of beryllium in copper as determined by ion and spark probe mass spectrometry

Diffusion profiles of Be in Cu, which extend over some millimeters, are studied laterally by both SSMS and SIMS. The diffusion of Be in Cu is investigated in the temperature range from 650 to 900 (± 5)°C for annealing times from 313 to 502 h. The Arrhenius equation is obeyed in the chosen temperature range. The diffusion coefficients obtained from both experimental approaches are in reasonable agreement.     

Single biosensor immunoassay for the detection of five aminoglycosides in reconstituted skimmed milk

The application of an optical biosensor (Biacore 3000), with four flow channels (Fcs), in combination with a mixture of four specific antibodies resulted in a competitive inhibition biosensor immunoassay (BIA) for the simultaneous detection of the five relevant aminoglycosides in reconstituted skimmed milk. Four aminoglycosides (gentamicin, neomycine, kanamycin and a streptomycin derivative) were immobilised onto the sensor surface of a biosensor chip (CM5) in the four Fcs of the biosensor system by amine coupling. In the Biacore, milk (reconstituted from skimmed milk powder) was 10 times diluted with a mixture of the four specific antibodies and injected through the four serially connected Fcs (1 min at a flow rate of 20 μl min⁻¹). The responses measured just prior to the injection (20 μl at a flow rate of 20 μl min⁻¹) of the regeneration solution (0.2 M NaOH + 20% acetonitril) were indicative for the presence or absence of the aminoglycosides in reconstituted milk. The limits of detection were between 15 and 60 ng ml⁻¹, which was far below the maximum residue limits (MRLs) (varying from 100 to 500 ng ml⁻¹) and the total run time between samples was 7 min.     

New materials from telechelic polyacetals

Telechelic polyacetals, obtained by cationic ring-opening polymerization of 1,3-dioxolane (DXL) and 1,3-dioxepane (DXP), have been used as building blocks for polymer materials. In the first part of this paper, the synthesis and the properties of networks based on polyDXL α,ω-bis(methacrylates) are discussed. The second part deals with the synthesis and the properties of polyacetal polyurethanes. A thermoplastic polyurethane was prepared with poly(DXL-co-DXP) α,ω-diol as soft segment and the combination butane-1,4-diol and hexamethylene diisocyanate as hard segment. Polyurethane networks were obtained from polyacetal polyols and diphenylmethane diisocyanate (MDI). Some physical properties of these new materials are reported.     

Determination of polybutylene terephthalate polycondensation equilibrium constant using a batch reactor

The PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m - cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 equation/tex2gif-stack-1.gif). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory - Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics.