Joseph P. Dougherty

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.

Laser-excited atomic-fluorescence spectrometry in an electrothermal atomizer with Zeeman background correction.

A pulsed excimer-pumped dye laser was used to excite atomic flourescence in graphite tube electrothermal atomizer. A 60-Hz ac magnitude field was applied around the atomizer and parallel to the excitation beam, for Zeeman background correction. The correction system was found to degrade the detection limits for silver, cobalt, indium, manganese, lead, and thallium by a factor of between 1 and 10. An increase in magnetic field strength, or a decrease in laser linewidth, should improve the detection limits, but was not possible here. For copper, the application of Zeeman background correction was unsuccessfull because the instrumentation was unable to resolve the sigma components from the laser emission profile sufficiently during the background correction measurement. For elements that exhibit sufficient Zeeman splitting, the linear dynamic range was the same with or without background correction Zeeman background correction was used to correct for scatter, in the resonance flourescence determination of manganese in a zinc chloride matrix and in mouse brain tissue.

Diagnostic studies of the Zeeman effect for laser excited atomic fluorescence spectrometry in an electrothermal atomizer

Abstract Reported here are the effects of various theoretical and experimental parameters on the sensitivities and calibration ranges of Zeeman background corrected, electrothermal atomizer, laser excited atomic fluorescence spectrometry. The experimental arrangement included a pulsed excimer pumped dye laser, and a graphite tube electrothermal atomizer, with laser excitation occuring parallel to the field lines of an a.c. electromagnet. The influences of Zeeman splitting, applied field strength, laser excitation linewidth, and atomic spectral profile, on the detection limits and linear calibration ranges were studied for six elements (Ag, Co, Cu, In, Pb, Tl). At low analyte concentrations, when the magnetic field is on, overlap of the Zeeman sigma components with the laser emission profile can degrade the sensitivities. The linear ranges of calibration curves with, or without Zeeman background correction were similar for those elements that exhibited sufficient Zeeman splitting. At high concentrations (greater than 100 ng, or 10 μg ml ), broadening of the atomic spectral profile caused an increase in the sigma component overlap and some of the calibration curves became double valued (rollover).

Precision Considerations in the Determination of Manganese in Mouse Brains by Furnace Atomic Absorption with Zeeman Background Correction

Abstract A method is presented for the determination of manganese in mouse brains by furnace atomic absorption with Zeeman background correction. Precision for the method of standard additions is compared with that of aqueous calibration curves. NBS bovine liver SRM is analyzed to verify the accuracy of the method.

Nonlinearity of Calibration Graphs for Laser-Excited Atomic Fluorescence in Graphite-Tube Atomizers

Calibration graphs for Laser-Excited Atomic Fluorescence Spectrometry (LEAFS) were constructed for graphite-tube electrothermal atomizers (ETAs). Laser radiation was propagated through holes in the side of the tubes, and atomic fluorescence was detected at a right angle through the bore of the tube. The LEAFS calibration graphs, while linear with a relative slope of one for 4 to 6 orders of magnitude, became nonlinear at high analyte concentrations. Observations concerning this nonlinearity are presented here. The onset of nonlinearity was believed to be primarily caused by post-filter effects. For nonresonance LEAFS, long lifetimes for the terminating energy levels in the fluorescence processes were believed to increase the probability of post-filter effects and subsequently to increase curvature of calibration graphs. Those conditions that increased the residence time of atoms in the furnaces (i.e., no internal gas flow and platform atomization) appeared to also increase post-filter effects and thus increased the amount of curvature of the calibration graphs.

Microwave Excited Electrodeless Discharge Lamps as Intense Sources for Zeeman Atomic Absorption Spectrometry

Abstract The use of manganese microwave excited electrodeless discharge lamps is examined in a commercial atomic absorption instrument with Zeeman background correction. The EDLs are compared to hollow cathode lamps for stability, intensity and linearity of calibration curves in atomic absorption.