PULSED AND TRANSIENT-MODES OF ATOMIZATION BY CATHODIC SPUTTERING IN A GLOW-DISCHARGE FOR ATOMIC-ABSORPTION SPECTROMETRY

Analytical applications of cathodic sputtering in a glow discharge have almost wholly involved the production of a steady-state atomic vapor from a bulk solid. Kinetic limitations result in relatively poor sensitivity and limit of detection for the steady-state mode of atomization. A method that overcomes these limitations, using the rapid production of analyte atoms to produce a greater transient concentration of atoms In the analysis volume than is possible for the steady-state mode of atomization, is described In this paper. Two new modes of atomization are presented. The transient mode of atomization uses a high-power discharge for the rapid production of analyte atoms, whereas the pulsed mode of atomization uses a discharge of much shorter duration and higher power to achieve even faster atomization than is possible with the transient mode of atomization. An important factor leading to faster production of analyte atoms is the difference In bonding between the solution residues and the solid, bulk samples as the source of atoms. The faster kinetics of atom formation for the pulsed and the transient mode of atomization result In better (sometimes, much better) sensitivity for these modes of atomization compared to the steady-state mode of atomization. Since both the pulsed and the transient mode of atomization are based on faster production of analyte atoms and differ In that in the former a short (milliseconds) duration discharge is used, whereas in the latter a long (seconds) duration discharge Is used, they are treated together as a new analytical technique. The new analytical technique and the conventional steady-state vapor technique have been evaluated by using a commercially available cathodic sputtering atomizer, Atomsource. These techniques have been characterized by kinetic modeling, and the superiority of the new analytical technique in sensitivity over the conventional technique based on the steady-state atomic vapor is shown. The sensitivity of the new analytical technique Is, In some cases, similar to or greater than that of graphite furnace atomic absorption spectrometry. Factors affecting the sensitivity and areas for future Improvement are discussed. The performance of the new analytical technique is also discussed In terms of the linear dynamic range of analytical calibration curves, Interferences, and recoveries. Interferences seem to depend on whether the matrix is conducting or not. The use of peak-area absorbance, rather than peak-height absorbance, has been found to eliminate interferences when the matrix Is conducting. A way to eliminate Interferences for nonconducting matrices is suggested. © 1990, American Chemical Society. All rights reserved.