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

Abstract

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.