This contribution reports on the development of an atmospheric pressure photoionization (APPI) source interfacing a gas chromatograph (GC) with a bench-top Orbitrap high resolution mass spectrometer (MS). We present efforts on method development aiming at high temperature stability (325°C), constant low impurity levels upon prolonged source operation, and efficient reaction volume irradiation combined with minimum peak broadening. The performance throughout each iterative development step was carefully assessed. The final GC-APPI-MS setup demonstrated femtogram-on-column sensitivity and chromatographic peaks of Gaussian shape with base peak widths <2 s for even the highest boiling compounds present in different EPA standard mixtures.
Molecular structures of the most prominent chiral non‐racemic hypervalent iodine(III) reagents to date have been elucidated for the first time. The formation of a chirally induced supramolecular scaffold based on a selective hydrogen‐bonding arrangement provides an explanation for the consistently high asymmetric induction with these reagents. As an exploratory example, their scope as chiral catalysts was extended to the enantioselective dioxygenation of alkenes. A series of terminal styrenes are converted into the corresponding vicinal diacetoxylation products under mild conditions and provide the proof of principle for a truly intermolecular asymmetric alkene oxidation under iodine(I/III) catalysis. 相似文献
The efficiency of miniaturized liquid chromatography columns with inner diameters between 200 and 300 μm has been investigated using a dedicated micro‐liquid chromatography system. Fully porous, core–shell and monolithic commercially available stationary phases were compared applying van Deemter and kinetic plot analysis. The sub‐2 μm fully porous as well as the 2.7 μm core–shell particle packed columns showed superior efficiency and similar values for the minimum reduced plate heights (2.56–2.69) before correction for extra‐column contribution compared to normal‐bore columns. Moreover, the influence of extra‐column contribution was investigated to demonstrate the difference between apparent and intrinsic efficiency by replacing the column by a zero dead volume union to determine the band spreading caused by the system. It was demonstrated that 72% of the intrinsic efficiency could be reached. The results of the kinetic plot analysis indicate the superior performance of the sub‐2 μm fully porous particle packed column for ultra‐fast liquid chromatography. 相似文献
The origin of fatty acids in milk has not been elucidated in detail. We investigated the contribution of dietary α-linolenic acid (ALA) to human milk fat, its oxidation and endogenous conversion to long-chain polyunsaturated fatty acids. Ten lactating women were given 13C-ALA orally, and breath and milk samples were collected for a five-day period, while dietary intakes were assessed. 37.5?±?2.7?% (M?±?SE) of the tracer was recovered in breath-CO2, and 7.3?±?1.1?% was directly transferred into milk. About 0.25?% of the tracer was found in milk long-chain polyunsaturated fatty acids. Combining intake and milk data, we estimate that about 65?% of milk ALA is directly derived from maternal diet. Thus, the major portion of milk ALA is directly derived from the diet, but dietary ALA does not seem to contribute much as a precursor to milk n-3 long-chain polyunsaturated fatty acids within the studied time period. 相似文献
Trirheniumdecaoxide, Re3O10, was obtained by the reaction of ReO2 and ReO3 in an arc-melting furnace. X-ray powder diffraction revealed a tetragonal structure with space group Im2 and lattice constants a=5.171(1) and c=13.371(6) Å. The crystal structure is built up by layers of corner-sharing [ReO5] square pyramids perpendicular to [001] with the apical oxygen pointing up and down alternatingly. These layers are interconnected by disordered [ReO6] octahedra. Early reports on Re2O5 are reviewed in the light of our results. 相似文献
The Crystal Structure of Lithiummetaperiodate, LiIO4 For the first time single crystals of LiIO4 were obtained. According to the results of an X-ray structure determination (monoclinic, P21/n; a = 525.5(3), b = 851.1(4), c = 796.9(5) pm, β = 104.21(3)°; Z = 4; 2 148 diffractometer data, R = 0.024) the coordination by oxygen is tetrahedral for iodine and strongly distorted trigonal bipyramidal for lithium. Two lithium-oxygen-polyhedra are connected via a common edge. LiIO4 crystallises isostructural to LiAlH4. The structure is discussed and compared to those of other metaperiodates and tetrahydridoaluminates. 相似文献