Development of stir-bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry for the analysis of musks in vegetables and amended soils

The aim of this study was to develop a sensitive and environment-friendly method based on stir-bar sorptive extraction (SBSE) followed by thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS) to determine 8 synthetic musks (musk ambrette, musk ketone, celestolide, tonalide, galaxolide, phantolide, traseolide, and cashmeran) in vegetables (lettuce, carrot, and pepper) and amended soil samples. In a first step sorptive extraction was studied both in the headspace (HSSE) and in the immerse mode (SBSE). The best results were obtained in the immersion mode which was further studied. The influence of the main factors: methanol (20%) and NaCl addition (0%), extraction temperature (40 °C) and time (180 min), extraction solvent volume (9 mL) and stirring rate (600 rpm) on the efficiency of SBSE was evaluated by means of experimental designs. In the case of TD, desorption time (10 min), desorption temperature (300 °C), cryo-focusing temperature (−30 °C), vent flow (75 mL/min) and vent pressure (7.2 psi) were studied using both a fractioned factorial design and a central composite design (CCD). The method was validated in terms of apparent recoveries (AR%), method detection limits (MDLs) and precision at two different concentration levels. Although quantification using instrumental calibration rendered odd results in most of the cases, satisfactory recoveries (74–126%) were obtained in the case of matrix-matched calibration approach for all of the analytes and matrices studied at the two concentration levels evaluated. MDLs in the range of 0.01–0.8 ng/g and 0.01–1.1 ng/g were obtained for vegetables and amended soil samples, respectively. RSD values within 1–23% were obtained for all the analytes and matrices. Finally, the method was applied to the determination of musks in vegetable and amended soil samples.     

The behaviour of the $$\overline{W}$$ -construction on the homotopy theory of bisimplicial sets

The codiagonal functor \(\overline{W}\) transfers a Quillen closed model structure on the bisimplicial set category from the ordinary model category of simplicial sets. This bisimplicial model structure is different from the so called Moerdijk model structure, which is similarly transferred from simplicial sets but through the diagonal functor. We show the mutual relationship of these two closed model structures on the category of bisimplicial sets.     

Synthesis of optically pure 1,2-diaryl- and 1,2-alkylaryl-1,2-amino sulfides

[reaction: see text] The reactions of the lithium (S)-alpha-(methylthio)-2-(p-toluenesulfinyl)benzyl carbanion with (S)-N-p-tolylsulfinyl aldimines evolve in a completely stereoselective manner providing a one-step synthesis of enantiomerically pure anti-1,2-disubstituted 1,2-amino sulfide derivatives.     

Evolution of crystallinity in photodegraded polyethylene films studied by ft-raman spectroscopy

FT-Raman spectroscopic studies of photodegraded polyethylene films have enabled the evolution of the crystallinity process to be measured. Commercial polyethylene films of M_w=90 000 were exposed in a weathering UV-chamber under known conditions of exposure time and radiant energy. The spectral profiles were modelled using Fourier methods. The relative amounts of the orthorrombic crystalline phase, α_c, the amorphous phase, α_a and the interphase, α_b, were calculated using Raman bands at 1416 cm⁻¹ characteristic of the crystalline phase and the bands at 1080, 1305 cm⁻¹, characteristic of the amorphous phase. The interphase content can be calculated from the relationship αb= 1-(α_c+α_a). It was found that the weathering process affects only the relative intensities of the bands attributed to crystalline and amorphous fractions; the crystalline content increases at the expenses of the amorphous fraction. These results are discussed in terms of the changes in the intermolecular forces caused by radiation exposure.