36 research outputs found
Characterisation and optimisation of a sample preparation method for the detection and quantification of atmospherically relevant carbonyl compounds in aqueous medium
Carbonyl compounds are ubiquitous in the atmosphere and either emitted primarily from anthropogenic and biogenic sources or they are produced secondarily from the oxidation of volatile organic compounds. Despite a number of studies about the quantification of carbonyl compounds a comprehensive description of optimised methods is scarce for the quantification of atmospherically relevant carbonyl compounds. The method optimisation was conducted for seven atmospherically relevant carbonyl compounds including acrolein, benzaldehyde, glyoxal, methyl glyoxal, methacrolein, methyl vinyl ketone and 2,3-butanedione. O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was used as derivatisation reagent and the formed oximes were detected by gas chromatography/mass spectrometry (GC/MS). With the present method quantification can be carried out for each carbonyl compound originating from fog, cloud and rain or sampled from the gas- and particle phase in water. Detection limits between 0.01 and 0.17 ÎŒmol Lâ1 were found, depending on carbonyl compounds. Furthermore, best results were found for the derivatisation with a PFBHA concentration of 0.43 mg mLâ1 for 24 h followed by a subsequent extraction with dichloromethane for 30 min at pH = 1. The optimised method was evaluated in the present study by the OH radical initiated oxidation of 3-methylbutanone in the aqueous phase. Methyl glyoxal and 2,3-butanedione were found to be oxidation products in the samples with a yield of 2% for methyl glyoxal and 14% for 2,3-butanedione after a reaction time of 5 h
Einfluss der initialen Fibrinogen/Albumin-Ratio auf die intrahospitale MortalitÀt bei Patienten mit spontaner intrazerebraler Blutung
Self-ordering within thin films of poly(olefin sulfone)s
A study has been performed of the manner in which two structural features of poly(olefin sulfone)s, helical backbones and calamitic side chains, create order in films. For this purpose copolymers were prepared with one (polymer I) or two (polymer III) cyanobiphenyls per residue, and terpolymers were prepared with both such residues diluted to below the 5% level within an otherwise poly(eicosene sulfone) chain (respectively, polymers II and IV). The polymers all have ordered phases according to X-ray powder diffraction studies on samples cooled from the melt, a layer spacing of about 45 Ă
being detected in the films as in the bulk. Those polymers with mainly eicosene sulfone residues had crystalline phases with large domains, the layers deriving from the helical backbones alone, the smectic A phases of the parent poly(eicosene sulfone) being either suppressed or reduced in extent by the presence of the aromatic moieties, which were almost randomly orientated. Those with one or two cyanobiphenyls per residue were liquid crystalline. In the latter the layer spacing derives from both backbone and side chains and is reduced when the residues bear a second mesogen as a consequence of a constraining effect from the stiff backbone, as a novel model predicts. The spacers give rise to a glass transition and segregate the planes in which the stiff backbones are assembled from the regions in which the aromatic groups aggregate on account of the strong ÏâÏ* interactions. Amorphous and optically isotropic spun cast films of these polymers became ordered on cooling from the melt or just on annealing, with the order, as determined by studies on the optical properties, being homeotropic for the aromatics and being planar for the backbones in a monodomain. For this arrangement we introduce the term homeo-planar smectic. Order parameters as high as 0.63 were measured for polymer I, from a clear film. The cyanobiphenyl chromophores formed H aggregates, with blue shifts in absorption and red shifts in fluoresence, and a little surprisingly these resulted in a circular dichroism, detectable when the films were inspected at an angle of 45° to the normal
Competition of Alignment and Aggregation? Phenomena in Constrained Films of LC Poly(Olefin Ulfone)s and Maleic Anhydride Co- and Terpolymers
Anisotropic films of functionalised polymers such as the liquid crystalline poly (olefin sulfone)s (POS) and maleic anhydride co- and terpolymers (MAC, containing azobenzene side-groups too) are studied. Starting from isotropic spin-coated films annealing results in homeotropically aligned films by spontaneous self-assembling. X-ray specular scattering (XRS) and X-ray grazing incidence diffraction (GIXD) indicate a layered structure across the film parallel to the interface and significant in-plane order in thin films. Polarised UV-VIS spectroscopy investigations show that the homeotropic orientation of the side groups causes the formation of âcard packedâ or H-aggregates. For azobenzene containing MAC terpolymer an initial UV-irradiation followed by a polarised VIS-irradiation causes a light-induced co-operative reorientation of both types of side-groups and results in a lamellar stacking which is tilted. Orientation and aggregation are therefore driven by the liquid crystallinity and the segregation tendency of POS and MAC in constrained films. This seems to be an important factor for such spontaneous ordering processes