Nachweis und Bestimmung organischer S?uren

Ohne Zusammenfassung     

The analysis of chlorinated dibenzofurans in municipal fly ash: Supercritical fluid extraction vs Soxhlet

A multiresidue supercritical fluid extraction procedure for chlorinated dibenzofurans (PCDFs) has been optimized as an efficient method for the determination of these compounds in fly ash samples. The results were compared with those obtained by Soxhlet extraction. Extracts from the two procedures were analyzed by gas chromatography–mass spectrometry (HRGC–MS) Statistical analysis of the results confirmed that supercritical fluid extraction provides data with a relative standard deviation of less than 10% while Soxhlet extraction data show a much greater spread.     

Polarisation characteristics of visible VCSELs

Vertical cavity surface emitting lasers (VCSELs) based on InGaP lase in the visible close to 650 nm. The polarisation characteristics of these devices are unlike other VCSELs in that they are stable and reproducible and show no switching with increased current. We describe the polarisation characteristics for such devices where the structures were grown on different orientation wafers. We show that polarisation selectivity increases directly with the degree of spontaneous ordering in the InGaP quantum wells, but not with the wafer offset angle.     

Eisen und Stab

Ohne Zusammenfassung     

Application of the unterzaucher method to the determination of oxygen in coke

The Unterzaucher method, used for the determination of oxygen in organic compounds and coal, has been adapted to the determination of oxygen in coke. Modifications were made to the conventional apparatus in order to eliminate any contribution made by the coke moisture to the determined oxygen content. The carbon dioxide produced from the combustion of the oxygen in the coke was estimated by a sensitive conductimetric method. Evidence is presented which indicates that additional liberation of oxygen from the coke mineral matter does not make a significant contribution to the total oxygen determined under the prescribed experimental conditions. The error of the determination is approximately 0.1%. A comparison is made between results obtained for a series of cokes and chars by the direct method and by an independent determination, based on neutron activation.     

The photodissociation of NO(2) by visible and ultraviolet light

We present velocity map images of the NO, O((3)P(J)) and O((1)S(0)) photofragments from NO(2) excited in the range 7.6 to 9.0 eV. The molecule was initially pumped with a visible photon between 2.82-2.95 eV (440-420 nm), below the first dissociation threshold. A second ultraviolet laser with photon energies between 4.77 and 6.05 eV (260-205 nm) was used to pump high-lying excited states of neutral NO(2) and/or probe neutral photoproducts. Analysis of the kinetic energy release spectra revealed that the NO photofragments were predominantly formed in their ground electronic state with little kinetic energy. The O((3)P(J)) and O((1)S(0)) kinetic energy distributions were also dominated by kinetically 'cold' fragments. We discuss the possible excitation schemes and conclude that the unstable photoexcited states probed in the experiment were Rydberg states coupled to dissociative valence states. We compare our results with recent time-resolved studies using similar excitation and probe photon energies.     

Air-trapping on biocompatible nanopatterns

The occurrence of air-trapping inside poly-eta-caprolactone nanopits was investigated by measuring the contact angles of water droplets on a set of defined nanotopographies. It is shown that the advancing angles follow the Cassie-Baxter theory, thus revealing the presence of air bubbles inside the biodegradable nanopatterns. The importance of these observations for the definition of hydrophilicity/hydrophobicity and in the context of in vitro cell behavior is discussed.     

Synthesis and luminescence of a charge-neutral, cyclometalated iridium(III) complex containing N--C--N- and C--N--C-coordinating terdentate ligands

The first examples of iridium(III) complexes containing a terdentate, N--C--N-coordinated 1,3-di(2-pyridyl)benzene derivative, cyclometalated at C2 of the benzene ring, are reported. This mode of binding becomes significant only if competitive cyclometalation at C4/C6 is blocked, and the ligand 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyxH) has been prepared to achieve this condition. The charge-neutral complex [Ir(dpyx)(dppy)], 2, (dppyH(2) = 2,6-diphenylpyridine) has been isolated, containing dpyx and dppy bound to the metal through one and two carbon atoms, respectively. A terpyridyl analogue, [Ir(dpyx)(ttpy)](PF(6))(2), 3, (ttpy = 4'-tolylterpyridine) has also been prepared and its X-ray crystal structure determined, confirming the N--C--N binding mode of dpyx. Complex 2 emits strongly in degassed solution at 295 K (lambda(max) = 585 nm, phi = 0.21, tau = 3900 ns, in CH(3)CN). In solution, the excited state can also undergo photodissociation, through cleavage of one of the Ir-C(dppy) bonds.     

A comparison of the Kjeldahl and Dumas methods for the determination of protein in foods,using data from a proficiency testing scheme

Both the Kjeldahl and the Dumas methods for the determination of protein in foodstuffs are currently in use, but the empirical nitrogen factors used to convert the determined nitrogen content to protein content are based on the Kjeldahl method alone. Non-equivalence between the two methods could therefore result in some laboratories reporting an incorrect protein content. We report here a study using data accumulated over several years in the results of a proficiency testing scheme. On average the Dumas method provided results that were relatively higher by about 1.4% than the Kjeldahl method, but the difference between the methods depended on the type of foodstuff. The methodology of looking for bias between analytical methods is critically discussed.