Gaschromatographische Bestimmung von Methoxyacetaldehyd neben Formaldehyd, Acetaldehyd und Glykolmethyl?ther

Zusammenfassung Eine gaschromatographische Methode zur Bestimmung von Formaldehyd, Acetaldehyd, Methoxyacetaldehyd und GlykolmethylÄther nebeneinander wurde entwickelt. Die Methode leistet gute Dienste bei der Kontrolle der ersten Stufe der Synthese von d-Cycloserin. Das Studium des Einflusses der verschiedenen Parameter auf die Ausbeute und der bei der heterogenen Katalyse verlaufenden Nebenreaktionen wird ermöglicht.

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Summary A gas-chromatographic method has been worked out for the determination of formaldehyde, acetaldehyde, methoxy acetaldehyde and glycolmethyl ether in presence of each other. It can be advantageously used for controlling the first stage of the synthesis of d-cycloserine. It also permits an investigation of the influence of the different parameters on the yield and an examination of the side-reactions involved in the heterogenous catalysis.

     

Direct Measurement of Emission of Endogenous Ozone from Plants by GC–MS-SIM

According to recent observations antibodies can catalyze the formation of previously unknown oxidants, dihydrogen trioxide (H₂O₃) and ozone (O₃), formed in the interaction between singlet oxygen (¹O₂) and H₂O. The O₃ molecules can be detected indirectly e.g. in TLC/OPLC chromatographic spots in the simple BioArena operating system using O₃-eliminating molecules in the culture medium. It is currently supposed that plants can be used for the direct detection of O₃ during its eventual emission from stomata. Using the fresh primary leaves of different plant species O₃ could be really detected by means of GC–MS-SIM from the space above the the leaves which were prepared in a CO₂-containing headspace vessel. It has been also established that the CO₂ also contained O₃ molecules, and therefore, we had to use a correction to the observed data. These new findings indicate that not only formaldehyde but also O₃ and their related bioreactive compounds may play a crucial role in disease resistance (e.g. in the mechanism of action of antibodies), cell proliferation and differentiation.     

Bessel beams: Effects of polarization

An approximation to a Bessel beam produced by tightly focusing linearly polarized light is known to produce a smaller central lobe than focusing plane polarized light. This is because the plane polarized wave gives a broad central lobe caused mainly by a parasitic longitudinal field component. It is known that this problem can be overcome by focusing radially polarized light. Here we demonstrate that other polarization distributions based on a linear combination of transverse electric (TE1) and transverse magnetic (TM1) fields can give a beam even narrower than for the radially polarized case. Special cases of this combination are identified, corresponding to the smallest width (TE1), and the maximum peak intensity compared with the side lobes (electric dipole polarization). Axially-symmetric forms can be generated by illumination with elliptically polarized light. A particular case is azimuthal polarization with a phase singularity, which is equivalent to TE1. For a semi-angular aperture of 60°, the TE1 case gives a central lobe width 9% narrower than for radially polarized illumination, while for plane polarized illumination it is 12% wider than the radially polarized case.     

Reductive amination of cyclohexanol/cyclohexanone to cyclohexylamine using SBA-15 supported copper catalysts

Amination of cyclohexanol was investigated in vapour phase over copper catalysts supported on mesoporous SBA-15. The different products identified during reductive amination of cyclohexanol reaction were cyclohexanone, cyclohexylamine, along with small amounts of N-Cyclohexylidinecyclohexylamine and dicyclohexylamine. Among several catalysts tested for the reductive amination, 5% Cu supported on SBA-15 exhibited better catalytic performance than other catalysts with 36% selectivity towards cylclohexylamine at 80% cyclohexanol conversion. The optimum reaction conditions employed to achieve the best catalyst performance were at 250 °C, 0.1 MPa of H₂/NH₃, TOS-10h. The active Cu sites, acidity of the catalyst, and effect of reaction parameters play a pivotal role in the reductive amination reaction. The prepared catalysts were characterized by XRD, BET, SEM, H₂-TPR and NH₃-TPD. The dispersion of Cu, particle size, and metal surface area (m²/g) calculated from pulse N₂O decomposition method. TPR findings reveal the presence of substantially dispersed copper oxide species at lower loadings which is easily reducible than the bulk copper oxide species found at higher Cu loadings. The acidity measurements by NH₃-TPD analysis suggest that the maximum acidic strength was obtained at 5 wt% copper on porous SBA-15, and decreased with Cu loadings. The catalytic properties are well in agreement with the findings of catalysts characterization.     

ArF laser excitation, collisional transfer, and quench-free fluorescence in I2/foreign gas mixtures

Fluorescence of I₂ excited by an ArF excimer laser at has been studied in the presence of 10 buffer gases (He, Ne, Ar, Kr, Xe, N₂, O₂, air, CF₄, and SF₆) over the pressure range from 0 to . At low pressure, the fluorescence is dominated by the bound-bound and bound-free (McLennan band) emission for . With increasing pressure, significant fractions of the D state population are collisionally transferred to the D′ state; this results in strong band flourescence at . A simple four-level model is developed to describe these processes. Quenching and transfer rate coefficients are measured for the 10 gases. With the exception of Xe, O₂, and air, which exhibit reactive quenching in addition to collisional quenching, the 340-nm-band fluorescence is resistant to quenching.     

Optical measurement of the speed of sound in air over the temperature range 300-650 K

Using laser-induced thermal acoustics (LITA), the speed of sound in room air (1 atm) is measured over the temperature range 300-650 K. Since the LITA apparatus maintains a fixed sound wavelength as temperature is varied, this temperature range simultaneously corresponds to a sound frequency range of 10-15 MHz. The data are compared to a published model and typically agree within 0.1%-0.4% at each of 21 temperatures.     

Kinetics of the reactions of isopropoxy radicals with NO,NO2, and O2

A fluorescence excitation spectrum of (CH₃)₂CHO (isopropoxy radical) is reported following photolysis of isopropyl nitrite at 355 nm. Rate constants for the reaction of isopropoxy with NO, NO₂, and O₂ have been measured as a function of pressure (1–50 Torr) and temperature (25–110°C) by monitoring isopropoxy radical concentrations using laser-induced fluorescence. We have obtained the following Arrhenius expressions for the reaction of isopropoxy with NO and O₂ respectively: (1.22±0.28)×10^?11 exp[(+0.62±0.14 kcal)/RT]cm²/s and (1.51±0.70)×10^?14 exp[(?0.39±0.28)kcal/RT]cm³/s where the uncertainties represent 2σ. The results with NO₂ are more complex, but indicate that reaction with NO₂ proceeds more rapidly than with NO contrary to previous reports. The pressure dependence of the thermal decomposition of the isopropoxy radical was studied at 104 and 133°C over a 300 Torr range using nitrogen as a buffer gas. The reaction is in the fall-off region over the entire range. Upper limits for the reaction of isopropoxy with acetaldehyde, isobutane, ethylene, and trimethyl ethylene are reported.We have performed the first LIF study of the isopropoxy radical. Arrhenius parameters were measured for the reaction of i-PrO with O₂, NO, NO₂, using direct radical measurement techniques. All reactions are in their high-pressure limits at a few Torr of pressure. The rate constant for the reactions of i-PrO with NO and NO₂ reactions exhibit a small negative activation energy. Studies of the i-PrO + NO₂ reaction produce data which indicate that O(³P) reacts rapidly with i-PrO. Unimolecular decomposition studies of i-PrO indicate that the reaction is in the fall-off region between 1 and 300 Torr of N₂ and the high-pressure limit is above 1 atmosphere of N₂.     

On the reduction of Holt's problem to a finite interval

Summary The reduction of Holt's problem to a finite interval is studied. We give the error estimate for the reduction. The solution of the boundary value problem is computed by a variant of the chasing method.This work was partly supported by the Hungarian Academic Research Foundation under project N⁰1-3-86-221     

The effect of molecular structure upon the response of the flame ionization detector

Summary It is known that the response of the FID is proportional to the number of carbon atoms in hydrocarbon molecules. If there is a heteroatom in the molecule, the response of the FID decreases. It is possible to calculate the sensitivity to any organic molecule if the signal-decreasing effect of a heteroatom or functional group is known. The sensitivity of a detector to an organic molecule containing heteroatoms is referenced to normal hydrocarbons by means of the effective carbon-atom number (ECN). Several authors have dealt with the determination ofECN values of different molecules and the effective carbon-atom number increment (ECN _inc) values for different functional groups and heteroatoms. In our previous work [1]ECN _inc values of several components were studied for homologous series. In this study we have investigated the effects of molecule structure upon ECN values by comparing theECN _inc of functional groups which are attached to molecules of different structure.     

Study of water transpiration features of sweet pepper using a thermal imaging system and non-destructive quality monitoring during post-harvest storage

Summary Sweet pepper is susceptible to relatively fast quality changes and its quality is influenced strongly by water or mass losses mainly due to transpiration processes during post-harvest. The aim of this study was the investigation of different storage conditions' effect on quality maintenance of pepper using surface thermal imaging, measurement of overall static stiffness and low-mass impact stiffness as non-destructive methods. Post-harvest keeping quality of pepper samples increased and unfavourable quality degradation was prevented under low, non-chilling temperatures together with the use of LDPE-packaging film resulted in high quality and fresh appearance after more than two weeks long storage period.