Characterization and Application of a Circular Thin Film Plasma Source for Atomic Emission Spectroscopy.

A circular silver thin film plasma source for the direct elemental analysis of suspended particles was evaluated. Silver films can be deposited on membrane filters without affecting their filtering ability. These filters are used to collect a particle sample, and the silver film and sample are vaporized by a high-voltage, high-current, electrical discharge. Elements present in the sample, film, and support gas emit continuum and atomic line radiation. The shot-to-shot variation in continuum intensity, typically 5-10% RSD, determines analytical detection limits. A dual-channel direct reading photoelectric detector based on optical fibers was constructed to decrease background signal variability. A greater than twofold decrease was obtained, but performance was limited by effective slit width of the optical fibers and relatively poor gain stability of the detectors. The circular geometry results in an under-damped sinusoidal discharge whose duration was 70% longer than that from a linear geometry. Peak currents increased 3-24%, and analyte intensity increased up to tenfold. Parametric studies indicate that analyte line-to-background intensity ratios are not strongly dependent on the following discharge conditions: energy from 240 J to 960 J, inductance from 5 (mu)H to 1200 (mu)H, outer-electrode inside diameter from 19 mm to 38 mm, and support gas composition from 0% to 40% O(,2) in Ar. When the center electrode is initially cathodic, the line-to-background ratio is increased by up to 100%. Particle size effects are not as severe for the circular geometry as reported for the linear geometry. For a 1200 (mu)H, 960 J discharge, particles of less than 5-(mu)m diameter gave the lowest integrated intensity. Particles in the size ranges up to 30-(mu)m diameter resulted in up to 70% greater integrated intensity. The reverse situation was noted for a 5 (mu)H, 240 J discharge. Analytical curves for Mn, Pb, and V under various discharge conditions have log-log slopes of 0.7-0.9. Element recoveries from artificial suspensions ranged from 50% to about 400%. Values of 99% to 109% recovery were obtained when delayed integration time gates were used for Pb determination in NBS "Urban Particulate Matter".PhDAnalytical chemistryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159839/1/8402384.pd