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W Buscher

Publications and source records attributed to W Buscher.

8 recordsLinked to original sources
PubMed2001

Development of an element-selective monitoring system for adsorbable organic halogens (AOX) with plasma emission spectrometric detection for quasi-continuous waste-water analysis.

An automated quasi-continuously-operating monitor has been developed for element-selective analysis of adsorbable organic halogens (AOX) in water. After extensive optimization the automatic method was applied to the analysis of standard solutions and real waste water samples to prove its analytical applicability. The new instrument is based on the element-selective analysis of halogens by means of a spectroscopic detection system consisting of a microwave-induced helium plasma excitation source (TM010-type; developed in this laboratory) and the plasma emission detector (PED) which operates with oscillating narrow-band interference filters. After enriching the organic components on activated charcoal and pyrolysis in an oxygen stream at 950 degrees C, in accordance with DIN/EN 38409,H14/1485, interfering CO2 and H2O gas generated during combustion is removed from the analytes in the so-called ELSA-system (element-selective AOX-analyzer). For focused injection into the plasma excitation source the analytes (hydrogen halides) are trapped in a deactivated fused silica capillary at -180 degrees C; this is followed by identification and quantification on the basis of element-specific emission of radiation in the VIS and NIR-region (chlorine 837.6 nm, fluorine 685.6 nm). Bromine and iodine could not be detected with satisfactory inter-element selectivity, because of spectral interferences caused by matrix elements, and so results from the respective single-element investigations for determination of AOBr and AOI are not presented. The procedure has been validated and the analytical performance has been examined by calibration with p-chlorophenol and p-fluorophenol. The limit of detection was 1.1 microg (absolute) for chlorine and 6.6 microg (absolute) for fluorine.

Flow Injection Analysis↗
PubMed1996

Speciation of mercury, platinum and tin - focus of research and future developments.

A discussion about the elements mercury, platinum and tin and their organometallic compounds, with special attention to important aspects like anthropogenic emissions, use in industry, agriculture and medicine, toxicities, biogeochemical cycles, highlights the necessity of speciation analysis. Methods frequently used to speciate mercury, platinum and tin compounds in different matrices are summarized. Future trends are indicated in order to give an impression about the importance of metal speciation and its increasing impact on some key disciplines.

Journal Article↗
PubMed1996

Frequency-modulated simultaneous Atomic Absorption Spectrometry (FremsAAS): Determination of As, Se and Sb.

The evaluation of accuracy and efficiency of the frequency-modulated simultaneous Atomic Absorption Spectrometry (FremsAAS) has been extended to an arrangement with EDL as light sources. Fundamental calibrations have been worked out for As, Se and Sb using a graphite furnace as well as hydride generation in combination with a heated quartz tube as atomization unit. The characteristic data are in good agreement with results obtained by conventional single-channel AAS instruments. Determinations in three standard reference materials with different complex matrices resulted in complete agreement with the certified values.

Journal Article↗
PubMed1990

Measuring threshold of reinforcing brain stimulation by the method of constant stimuli.

A new method for measuring threshold of reinforcing electrical brain stimulation is described and results of a parametric study using this method are presented. Two groups of rats were trained under a concurrent FR-CRF (fixed ratio-continuous reinforcement) schedule of reinforcement provided by electrical stimulation of the lateral hypothalamus. The invariant intermittent FR schedule of reinforcement was used to maintain a baseline of behavior while a superimposed concurrent CRF schedule was used to measure reinforcement magnitude by varying the intensity of the CRF stimulus between zero and a maximum. Increasing and decreasing stimulus intensity on the CRF schedule leads to a gradual disappearance, respectively reappearance, of post-reinforcement pauses (PRPs) on the concurrent FR schedule, providing a criterion for changeover in schedule control, and thus, for threshold of reinforcement. To illustrate the measurement of threshold according to psychophysical requirements of the Method of Constant Stimuli, different CRF intensities were given in a randomized order. In one group of animals FR and CRF stimuli were given through the same electrode. Another group received FR and CRF stimuli through separate electrodes implanted in different hemispheres of the brain. For both groups the duration of the PRP was used as the dependent variable. The data of both groups showed a high negative correlation between the intensity of the CRF stimulus and the duration of the PRP, which is consistent with the results of experiments in which a Method of Limits procedure was used. On the basis of this relationship between CRF current intensity and PRP duration a threshold for reinforcing brain stimulation was calculated.

Animals↗
PubMed1989

Interhemispheric relationship between lateral hypothalamic self-stimulation and the region of the nucleus tegmenti pedunculo-pontinus.

Electrical self-stimulation in the lateral hypothalamus was recorded in both hemispheres of 20 rats before and after making a lesion either by unilateral radiofrequency stimulation or by injection of N-methyl-D,L-aspartate into the region of the peduncular-pontine nucleus. For the animals which received the radiofrequency lesion, a rate-intensity function was established for 3 stimulation intensities 3 days before and 5 days after the lesion. For the animals in which N-methyl-D,L-aspartate was injected, a reinforcement threshold was measured 3 days before and after the lesion using a psychophysical method-of-limits procedure. With the rate-intensity procedure a decrease in the rate of self-stimulation was observed at the highest stimulation intensity through the electrode situated contralateral to the side of the lesion. Similarly, with the reinforcement threshold method, a significant increase in threshold was found from the electrode placed in the hemisphere contralateral but not ipsilateral to the site of the lesion. These data suggest an involvement of primarily crossed pathways coursing to or from the peduncular-pontine nucleus as being involved in the control of lateral hypothalamic self-stimulation.

Animals↗
PubMed1987

Lateralized functional relationship between the preoptic area and lateral hypothalamic reinforcement.

Electrical self-stimulation in the lateral hypothalamus of both hemispheres was recorded in 14 rats before and after administration of a unilateral ibotenic acid lesion of the cell bodies in the region of the lateral preoptic area. A significant decrease in the rate of self-stimulation at each of two stimulation intensities was found when the electrode was placed in the hemisphere in which the ibotenic acid lesion was made. This decrease remained constant over 21 days of testing. No changes were detected in rate of self-stimulation in the intact contralateral hemisphere. These results provide evidence for a role in lateral hypothalamic self-stimulation of intrinsic neurons located in the region of the lateral preoptic area.

Animals↗
PubMed1983

Hypothalamic self-stimulation in rats with one hemisphere isolated anterior to the midbrain and the other hemisphere devoid of the telencephalon.

The telencephalon was removed unilaterally in rats. In addition, the forebrain of the other hemisphere was isolated from its brain stem by a precollicular transverse cut. This preparation was then tested for self-stimulation via electrodes implanted in the region of the lateral hypothalamus and medial forebrain bundle (LH-MFB) of either hemisphere. Self-stimulation was found to be intact in both hemispheres. Possible pathways connecting the LH-MFB region of one hemisphere to the contralateral diencephalon were also investigated in the bilaterally detelencephalized rat. The technique of retrograde transport of horseradish peroxidase was used for this purpose. Some fibers from the LH-MFB of one hemisphere were found to decussate to the other hemisphere by way of the thalamic commissure. The supraoptic decussation as well as diffusely organized interdiencephalic connections provide additional routes for interhemispheric LH-MFB projections.

Animals↗