Robert G. Michel

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.

Laser excited atomic fluorescence spectrometry — a review☆

Abstract This review focuses on the development of new instruments, and new applications of laser excited atomic fluorescence spectrometry, LEAFS, in recent years since the last published reviews. Such developments include solid-state tunable lasers, deep UV tunable lasers, the use of charge coupled detectors (CCDs), and the applications of LEAFS for trace metal determination in various samples. The advent of diode lasers with their now somewhat improved range of wavelengths and power output, provides opportunities for research and applications in LEAFS. The further development of the coupling of second and third harmonic crystals to pulsed diode lasers shows promise for compact and robust instrumentation. There have been no recent instrumental developments that might provide more isotopic selectivity beyond the elements like uranium where the spectral isotope splitting is greater than most elements, but laser diodes could provide this due to their potential to provide an output with very narrow spectral bandwidth. The advent of optical parametric oscillator-based lasers has enabled LEAFS to be much more practical then in the past when dye lasers were used. This should be the harbinger of more applications of LEAFS to complex real sample analyses that can not be done by other techniques for reasons of sensitivity or selectivity. Array detectors provide an additional degree of freedom by provision of more spectral information more rapidly, which should aid the study of complex samples that might produce complex background problems. The recent literature indicates that the sensitivity, selectivity and ease of method development of LEAFS is well-established, and that there are no substantial analytical disadvantages to the technique beyond the instrumental limitations associated with the single element at a time mode of operation and the complexity of the laser systems. Laser technology continues to develop rapidly, which heralds a bright future for LEAFS.

Determination of ultra-trace amounts of cobalt in ocean water by laser-excited atomic fluorescence spectrometry in a graphite electrothermal atomizer with semi on-line flow injection preconcentration

A method has been developed for the determination of trace and ultra-trace amounts of cobalt in sea-water. Samples of CASS-2 Nearshore Seawater and NASS-4 Open Ocean Water reference materials from the National Research Council of Canada were employed. Laser-excited atomic fluorescence spectrometry in an electrothermal atomizer (ET-LEAFS) was used, and integrated with semi on-line flow injection microcolumn preconcentration. For cobalt, the effects of pH on the preconcentration efficiency, the concentration of the chelating agent and the distribution of cobalt in the ethanol eluate were studied. A bonded silica, with octadecyl functional groups (C18) in a 10 µl column, was employed for preconcentration of cobalt in ocean water. Ocean water volumes of 0.40 and 1.00 ml were required for the determination of cobalt in CASS-2 and NASS-4, respectively. These volumes were almost two orders of magnitude smaller than those required by inductively coupled plasma mass spectrometry and some other competitive techniques. The preconcentration factors were 5- and 12.5-fold for CASS-2 and NASS-4, respectively. The detection limits (3s), based on 12.5-fold preconcentration, were 0.08 and 1.0 ng l–1 for cobalt in aqueous standard solutions and in Ocean Water Reference Materials, respectively. Results for the determination of cobalt in CASS-2 and NASS-4 showed that there were no significant differences between the certified values and the measured values, based on Students t-test at the 95% confidence level. The relative standard deviations for the determinations of the concentrations of cobalt in CASS-2 and NASS-4 were 9 and 13%, respectively.

A REVIEW OF RECENT APPLICATIONS OF NEAR INFRARED SPECTROSCOPY, AND OF THE CHARACTERISTICS OF A NOVEL PbS CCD ARRAY-BASED NEAR-INFRARED SPECTROMETER

ABSTRACT Near-infrared spectroscopy (NIRS) has been gaining popularity as an analytical tool due to advances in the power of personal computers, which allow the extraction of chemical and physical information about a sample, and the utilization of cost efficient and robust CCD array-based spectrometers. In this review, applications of NIRS are explored, within various fields of analytical chemistry, which take advantage of the inherent rapid analysis time and minimal sample preparation that is possible. For the purposes of illustration, the usefulness and limitations of a novel, PbS array-based spectrometer are described in the context of its application to the analysis of a variety of samples.

Determination of Thallium, Manganese, and Lead in Food and Agricultural Standard Reference Materials by Electrothermal Atomizer Laser-Excited Atomic Fluorescence and Atomic Absorption Spectrometry with Slurry Sampling

Electrothermal atomizer laser-excited atomic fluorescence spectrometry (ETA LEAFS) and electrothermal atomic absorption spectrometry (ETA AAS) have been compared for the determination of three elements in National Institute of Standards and Technology food and agricultural standard reference materials with dissolved and slurried samples. Advantages of slurry sampling include reduced sample preparation and a reduced risk of contamination. ETA LEAFS is an extremely sensitive technique, with detection limits one to four orders of magnitude more sensitive than ETA AAS. Using the front-surface illumination approach, this paper reports the first application of a modern, unmodified graphite tube furnace for the determination of manganese, thallium, and lead in biological materials by ETA LEAFS. Thallium was determined by ETA LEAFS at levels one to two orders of magnitude below the ETA AAS detection limit. The determinations done by ETA LEAFS with the use of either dissolved or slurry sampling agreed well with the certified values, with typical analytical RSDs between 3 and 10%. These precisions were similar to the precisions of the ETA AAS measurements. For ETA AAS, the sizes of the background signals reported in the literature are often about the same order of magnitude as the analytical signal. In this work, the sizes of the background signals for ETA LEAFS were shown to be negligible relative to the fluorescence signals for most samples investigated. The relatively small size for the ETA LEAFS background signals, when compared to ETA AAS background signals, indicates that background correction errors are less likely, and that stringent specifications might be unnecessary for ETA LEAFS background correction instrumentation.

Resonant Laser Ablation of Metals Detected by Atomic Emission in a Microwave Plasma and by Inductively Coupled Plasma Mass Spectrometry

It has been shown that an increase in sensitivity and selectivity of detection of an analyte can be achieved by tuning the ablation laser wavelength to match that of a resonant gas-phase transition of that analyte. This has been termed resonant laser ablation (RLA). For a pulsed tunable nanosecond laser, the data presented here illustrate the resonant enhancement effect in pure copper and aluminum samples, chromium oxide thin films, and for trace molybdenum in stainless steel samples, and indicate two main characteristics of the RLA phenomenon. The first is that there is an increase in the number of atoms ablated from the surface. The second is that the bandwidth of the wavelength dependence of the ablation is on the order of 1 nm. The effect was found to be virtually identical whether the atoms were detected by use of a microwave-induced plasma with atomic emission detection, by an inductively coupled plasma with mass spectrometric detection, or by observation of the number of laser pulses required to penetrate through thin films. The data indicate that a distinct ablation laser wavelength dependence exists, probably initiated via resonant radiation trapping, and accompanied by collisional broadening. Desorption contributions through radiation trapping are substantiated by changes in crater morphology as a function of wavelength and by the relatively broad linewidth of the ablation laser wavelength scans, compared to gas-phase excitation spectra. Also, other experiments with thin films demonstrate the existence of a distinct laser–material interaction and suggest that a combination of desorption induced by electronic transition (DIET) with resonant radiation trapping could assist in the enhancement of desorption yields. These results were obtained by a detailed inspection of the effect of the wavelength of the ablation laser over a narrow range of energy densities that lie between the threshold of laser-induced desorption of species and the usual analytical ablation regime. Normal ablation employs high-power lasers in an attempt to create a vapor plume without selective vaporization, and with a stoichiometry that accurately represents the stoichiometry of species in the solid sample. RLA, as a method of selective vaporization, appears to provide an opportunity to exploit selective vaporization in new ways.

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.

A novel method of wavelength modulation for atomic spectrometry—some preliminary experiments

The method of wavelength modulation most commonly used in atomic spectrometry employs an oscillating refractor plate driven by a scanning motor. A new mechanical arrangement is described, which involves a rotating quartz mechanical chopper. This quartz chopper is composed of four quadrants of different thickness, which refract radiation by different degrees. The rotating quartz chopper is placed inside the monochromator in a position similar to that used for oscillating refractor plates. Efficient wavelength modulation is achieved. However, the rotating quartz chopper has the advantage that a good square-wave modulation function is obtained.

Direct solid sampling of nickel based alloys by graphite furnace atomic absorption spectrometry with aqueous calibration

Abstract The direct analysis of solid nickel based alloy samples was investigated using graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction and a Perkin-Elmer solid sampling cup accessory. Advantages of direct solid sampling include high sensitivity and reduced risk of sample contamination since no dissolution step is used. Using aqueous standards and STPF technology with Zeeman background correction, it has proved possible to analyze small chips of nickel based alloy directly. High temperature alloy standard reference materials (SRMs) were accurately analyzed for low and sub ppm concentrations of the trace metals thallium, bismuth, tellurium, selenium and lead in the alloys. Analyses were done on single alloy chips weighing between 0.5 and 4 mg with typical analytical RSDs of 6–14%.

Signal and noise considerations of non-dispersive laser-excited atomic fluorescence in a graphite tube atomiser with front-surface illumination

A commercial graphite tube electrothermal atomiser (ETA) was used as an atom cell for laser-excited atomic fluorescence spectrometry (LEAFS). From the point of view of signal to noise ratio (S/N), both transverse and front-surface illumination of the furnace were investigated, together with dispersive and non-dispersive fluorescence detection. Front-surface illumination offered better sensitivity, due to better illumination efficiency, than transverse detection. Non-dispersive detection had better light gathering power, hence better sensitivity, than dispersive detection. The effects of optical filter bandpass and slit-width on the S/N of non-dispersive detection were explored. Narrow bandpass filters cut down the noise and led to improvements in limits of detection (LOD). Sub-femtogram (sub-10–15 g) LODs for TI and Pb were obtained by using very narrow (1-nm) bandpass filters and non-dispersive detection of the fluorescence.