Electrostatic influence on rotational mobilities of sol-gel-encapsulated solutes by NMR and EPR spectroscopies

The rotational mobilities of small solute molecules encapsulated in tetramethyl orthosilicate (TMOS) sol-gels have been investigated by EPR spectroscopy of encapsulated nitroxide probes and by high-resolution NMR spectroscopic measurements of transferred NOE's (trNOE's), of T(1)'s, and of T(1)'s in the rotating frame (T(1)rho). The two spectroscopic methods are sensitive to motions on different time scales and hence, are nicely complementary. Suites of neutral, positively, and negatively charged nitroxide probes (EPR) and of simple diamagnetic small molecules (NMR) were selected to disclose influences of electrostatic interactions with the sol-gel walls and to probe the presence of multiple populations of molecules in distinct regions of the sol-gel pores. For neutral and negatively charged solute probes, both techniques disclose a single population with a significantly increased average rotational correlation time, which we interpret at least in part as resulting from exchange between free-volume and transiently immobilized surface populations. The electrostatic attraction between cationic probes and the negatively charged sol-gel walls causes the positively charged probes to be more effectively immobilized and/or causes a greater percentage of probes to undergo this transient immobilization. The EPR spectra directly disclose a population of cationic probes which are immobilized on the X-band EPR time scale: tau(c) greater than or approximately equal 10(-7) s. However, NMR measurements of trNOE's and of T(1)rho demonstrate that this population does exchange with the free-volume probes on the slower time scale of NMR. This approach is equally applicable to the study of solutes within other types of confined spaces, as well.     

Λ-buildings and base change functors

We prove an analog of the base change functor of Λ-trees in the setting of generalized affine buildings. The proof is mainly based on local and global combinatorics of the associated spherical buildings. As an application we obtain that the class of generalized affine buildings is closed under taking ultracones and asymptotic cones. Other applications involve a complex of groups decompositions and fixed point theorems for certain classes of generalized affine buildings.     

Anthelmintics in bovine milk and muscle: interlaboratory studies among EU National Reference Laboratories

The paper describes in detail how to evaluate interlaboratory studies for the measurement of authorised and non-permitted veterinary drugs. Examples of different kinds of evaluation will be presented including the results of two interlaboratory studies for anthelmintics in bovine milk and muscle. As compared to an interlaboratory study 2008, a clear development regarding the proficiency of the laboratories of the European Residue Control System could be noted in 2009. As a result of this development, the percentage of false-negative and false-positive results had decreased considerably. The described improvements in the analysis of the included anthelmintics were also reflected in the overall assessment. While in 2008 ten (38.5?%) out of 26 NRLs fulfilled the proficiency criteria of the interlaboratory study, this number had increased to fourteen (53.8?%) by 2009. In some cases, the correct quantification needed to be improved.     

Determination of Acrylamide and Acrolein in Smoke from Tobacco and E-Cigarettes

Acrylamide and acrolein are two short-chained hazardous compounds with neurotoxic, carcinogenic, and mutagenic effects. The aim of this paper is to describe a fast and simple procedure for simultaneous determination of both acrylamide and acrolein under standard conditions, suggest a suitable calibration protocol for custom analysis, and demonstrate its applicability to the analysis of gaseous products from, e.g., cigarettes, cigars, or electronic cigarettes. A gas chromatography–mass spectrometry (GC–MS) method was developed to quantify acrylamide and acrolein in smoke vapor from electronic cigarettes, tobacco cigarettes, and cigars. Nonionic and highly polar molecules with a low boiling point and molecular mass need a suitable derivatization method to achieve appropriate retention and selectivity on commonly used relatively nonpolar stationary phases and to enhance the molecular mass for easy MS detection. The derivatization of acrylamide and acrolein was carried out by a bromination method with elemental bromine. The dibromo derivatives were extracted into an organic solvent and following a dehydrobromination procedure the samples were injected into the GC–MS system. Important experimental parameters were varied, after which the bromination time was defined as 30 min, and the injector temperature and the starting temperature of gradient were set at 280 and 50 °C respectively. Acrolein was found in all tested samples, while acrylamide was detected only in smoke from normal tobacco. Possible mechanisms for the formation of these unsaturated compounds in the samples are discussed. After its validation the newly developed method was successfully and reliably applied to the analysis of both compounds. This short method provides an easy way to determine acrylamide and acrolein in gaseous samples.

     

Critical re-investigation of the alditol acetate method for analysis of substituent distribution in methyl cellulose

The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility. Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained. Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error.     

Residual‐based artificial viscosity for simulation of turbulent compressible flow using adaptive finite element methods

In this paper, we present a finite element method with a residual‐based artificial viscosity for simulation of turbulent compressible flow, with adaptive mesh refinement based on a posteriori error estimation with sensitivity information from an associated dual problem. The artificial viscosity acts as a numerical stabilization, as shock capturing, and as turbulence capturing for large eddy simulation of turbulent flow. The adaptive method resolves parts of the flow indicated by the a posteriori error estimates but leaves shocks and turbulence under‐resolved in a large eddy simulation. The method is tested for examples in 2D and 3D and is validated against experimental data. Copyright © 2012 John Wiley & Sons, Ltd.     

A new profile likelihood confidence interval for the mean probability of detection in collaborative studies of binary test methods

A confidence interval for the probability of detection across laboratories (LPOD) for qualitative methods, described in the AOAC INTERNATIONAL guidelines for validation of microbiological methods for food and environmental surfaces, is considered. It is demonstrated that under certain conditions, the observed confidence of this confidence interval can be rather low, so that statistical minimum requirements are not fulfilled. A new profile likelihood confidence interval based on a latent random laboratory effect approach is proposed. Observed confidence levels for this confidence interval demonstrate its applicability already for a small number of laboratories.