In vivo sampling using loop microdialysis probes coupled to a liquid chromatograph.

Microdialysis probes with longer membranes (20-100 mm) provide increased relative recovery over traditional shorter probes (1-4 mm) developed for neuroscience applications. The characterization and optimization of "straight through" or "loop type" probes for use in subcutaneous tissue are considered. Membrane area, probe size, inlet and outlet tubing dimensions, and flow-rate are examined for their effects on relative recovery, the total collection rate, and bulk flow through the membrane wall. Polyacrylonitrile and regenerated cellulose membrane fibers with different geometries were compared. Sampling probes used fibers 3-10 cm long. Inlet and outlet tubing was varied from 25 to 110 microns I.D. with lengths of 10 to 50 cm. Probe configurations optimized for relative recovery, flow-rate, and utility for in vivo use are presented. Utilizing microdialysis probes with large membrane surface areas results in relative concentration recovery of greater than 50% at flow-rates of greater than 5 microliters/min. Therapeutic drug monitoring in subcutaneous tissue of awake animals is explored.     

In vivo microdialysis/liquid chromatography/tandem mass spectrometry for the on-line monitoring of melatonin in rat

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been coupled to in vivo microdialysis for on-line monitoring of melatonin in a freely moving rat for a period of 15 hours. A microdialysis probe was surgically implanted into the jugular vein of the rat, and deionized water was used as the perfusion medium at a flow rate of 1.0 microL/min. Microdialysis samples were collected in an on-line injector with sample injection every 30 minutes. Melatonin was dosed by intraperitoneal (i.p.) injection and then monitored by microdialysis/LC/MS/MS. The whole experiment, including the microdialysis sampling and sample injection into the LC/MS system, was fully automated. Metabolites of melatonin were identified off-line by LC/MSn experiments. Two metabolites were identified as 6-hydroxymelatonin and cyclic 2-hydroxymelatonin, consistent with ones found previously in the literature.     

Composition of oxygen precipitates in Czochralski silicon wafers investigated by STEM with EDX/EELS and FTIR spectroscopy

In this work, we investigated the stoichiometry of oxygen precipitates in Czochralski silicon wafers. The thickness dependence of the Cliff–Lorimer sensitivity factor for the silicon/oxygen system was determined and applied for the investigation of the stoichiometry of oxygen precipitates by EDX. The results show that both plate‐like oxygen precipitates and a transitional form between plate‐like and octahedral precipi‐ tates consist of SiO₂. This was confirmed by EELS low loss spectra where the typical spectrum for amorphous SiO₂ was observed. Moreover, the absorption band of plate‐like precipitates at 1227 cm^–1 was found in the low temperature FTIR spectrum. It was demonstrated that this band can only be simulated by the dielectric constants of amorphous SiO₂. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

On chemically vapour-deposited Si/Ge growth in a multi-wafer deposition process at atmospheric pressure

In multi-wafer deposition of Si/Ge thin films from silane, germane mixtures at low-temperature epitaxy conditions not only the depletion of the silicon source but also of the germanium source along the reactor tube axis has to be counteracted in order to get homogeneous layer thickness as well as composition. Carrier gas throughput must be minimized to have a sufficient effective chemical reaction rate at low temperature. Thus it cannot be used to flatten layer growth along the susceptor. Yet the addition of a chemically reactive gas, as for instance hydrogen chloride, is suitable to ensure a nearly constant content of the layer forming source gases along the reactor tube. On the other hand hydrogen chloride may infiltrate additional contaminants leading for instance to high oxygen concentration in the deposited layer. However, oxygen soluted or precipitated changes particular features of Si/Ge behaviour for instance during the thin film growth, the following technological stress of the wafer, or the running electronic structures of microelectronic devices.