Michael D. Seltzer

Brain manganese accumulation following systemic administration of different forms

The content and retention of manganese in the blood and brain of mice exposed to different forms of the metal was compared. Mice received an acute sc injection of manganese as the chloride or oxide (Mn3O4) or as the organic MMT. A single injection markedly elevated brain manganese concentrations within 1 day and elevated levels were maintained for at least 21 days. Repeated injections led to further increases in both brain and blood, although the levels in the brain appeared to persist at consistently high levels for longer periods. The chloride form produced higher brain levels than either of the other two forms. These results appear to suggest that the slowly developing neurotoxicity in response to manganese exposure may be due to a persistent retention of manganese by the brain.

Preparation of highly dispersed cobalt clusters in zeolites via microwave discharge methods

Abstract A microwave discharge has been used to prepare highly dispersed and reduced cobalt metal atom clusters in zeolites and other solid substrates such as alumina, silica, activated carbon, and polymers. Spectroscopic data show that the microwave discharge approach offers several advantages over other activation procedures for the preparation of small metal particles on solid supports. Scanning electron microscopy, ferromagnetic resonance, and X-ray line broadening experiments indicate that these particles are smaller than 30 A.

Laser excited atomic fluorescence for studies of enhancement effects in the direct current plasma

Abstract This paper reports a preliminary use of laser excited atomic fluorescence spectrometry (LEAFS) to study analyte population enhancement caused by easily ionized elements (EIEs) in the direct current plasma (DCP). Spatial atom density profiles in the DCP were obtained using resonance fluorescence at the calcium atom line at 422.7 nm, with and without the addition of an EIE. Variations in atom density caused by an EIE were found to be far too small to account for the marked enhancements of atomic emission signals which are caused by EIEs. Direct line fluorescence of the barium ion, excited at 614 nm and detected at 455 nm, was used to probe the effect of an EIE on excited state populations. Measurements in the analytical region of the plasma close to the core revealed that enhancements of fluorescence signals at low laser powers disappeared at laser powers which were sufficient to saturate the atomic transitions. While this result does not clarify any of the mechanisms of excitation in the DCP, it does lend support to two of the fundamental postulates of a recent model of the spectrochemical excitation processes in the DCP. These are first, that the analytical region of the DCP is not in local thermodynamic equilibrium (LTE) and second, that EIE enhancement proceeds by modulating the rates of power distribution among various plasma zones. In the outer zone of the analytical region of the DCP, depressive interferences occurred. These did not disappear upon saturation which indicates that they were not rate effects but effects that resulted from atom density changes.

An Active Nitrogen Plasma Atom Reservoir for Laser-Induced Ionization Spectrometry

Abstract A microwave-induced, atmospheric pressure active nitrogen plasma has been investigated as an atom reservoir for laser-induced ionlzation spectrometry. Discrete analyte samples were introduced into the active nitrogen plasma by a microarc atomizer. Both laser-enhanced ionizatlon (LEI) and dual laser ionlzation (DLI) were carried out in the plasma plume that extended from the Beenakker cavity.

Laser Excited Atomic Fluorescence in the Direct Current Plasma

Abstract Detection limits of between 3 and 72 ng mL−1 (barium, calcium, sodium, vanadium and iron) and linear dynamic ranges of just over four orders of magnitude (barium and calcium) are reported for laser excited atomic fluorescence spectrometry (LEAFS) in the three electrode direct current plasma. The detection limits are not as good as those that have been reported for LEAFS in both the inductively coupled plasma and flames. The limiting factors appear to be the high plasma background, scatter off sample droplets and the inefficiency of the sample introduction process.

Electrical characteristics of microwave-induced plasmas for laser-induced ionization spectrometry

Abstract The electrical properties of microwave-induced plasmas (MIPs), relevant to signal detection of laser-induced ionization, have been investigated. Direct current vs. applied voltage relationships have been characterized for both argon and argon-active nitrogen plasmas. Suppression of signal detection for laser-induced ionization in the active nitrogen plasma is similar to that encountered in flames in the presence of thermally-ionized Group IA elements.