John T. McCaffrey

Capacitive Discharge Circuit for Controlled Heating of Anisotropic Graphite Tubes: Part I:

Circuitry suitable for capacitive discharge heating of anisotropic graphite tubes for atomic absorption and atomic fluorescence is detailed and initial calibration data are presented.

Capacitive-Discharge Circuit for Controlled Heating of Anisotropic Graphite Tubes. Part II: Characterization for Graphite Furnace Atomic Absorption

Performance data from a recently described capacitive-discharge heating system are presented. The capacitive-discharge heating circuit, which used a 0.15 F capacitor bank, is shown to provide reproducible heating of a small anisotropic graphite tube (5 mm o.d. × 9 mm long, 1 mm wall thickness) at heating rates of up to 65°C per ms to a final temperature of 2500°C. The performance and resistance of graphite from two manufacturers are compared. The effect of the capacitor bank voltage on the heating rate and maximum achievable temperature is studied. Photographic and optical pyrometric evidence of the circumferential temperature anisotropy is presented. Pyrolytically coated anisotropic graphite tubes were investigated. Preliminary investigations using Pb indicated that sample deposition on the unbroken lamellar graphitic planes provides about 1.5 times the peak-area and peak-height sensitivity obtained from sample deposition across the lamellar planes.

Continuum source excited atomic fluorescence in the metastable nitrogen plasma

Abstract Source-modulated continuum source excited atomic fluorescence (AFC) detection limits were measured for 13 elements in a metastable nitrogen plasma atom cell which used a carbon furnace for sample introduction. The AFC detection limits were compared to wavelength-modulated atomic emission (AE) detection limits in the same atom cell under the same plasma conditions. AFC detection limits were 5 to 2500 times poorer than the AE detection limits. Increased background noise due to analyte AE was shown to be the primary reason for the poor AFC results.

Discrimination against atomic-emission spectral interferences in wavelength-modulated continuum source excited flame atomic-fluorescence spectrometry

The extent of spectral interferences at commonly used analytical atomicfluorescence lines was demonstrated to be severe enough to necessitate the exploration of possible instrumental approaches to discriminate against the more serious type of spectral interference, namely the atomic emission of concomitant metals in samples. Two novel methods of double modulation were incorporated into the instrumentation in order to allow such discrimination. The two methods were evaluated with respect to their effect on detection limits and their effect on the particularly severe interference of potassium emission at 404.4 nm on lead fluorescence at 405.8 nm.