EFFECTS OF MODIFIER MASS AND TEMPERATURE-GRADIENTS ON ANALYTE SENSITIVITY IN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY - INVITED LECTURE

The effects of various masses of some commonly used modifiers [palladium, copper, nickel, and palladium + magnesium nitrate] on the integrated absorbance sensitivity, under stabilized temperature platform furnace conditions in a Massmann-type atomizer, were studied. Typically, for larger masses of modifier, the analytical signal only slowly returned to the baseline. The reason for this tailing was investigated and it was found that the modifier changed the adsorption properties of the graphite surface at the cooler tube ends. Hence, signal tailing in the presence of a modifier can be attributed to secondary adsorption-desorption processes occurring at the tube ends. By leaching experiments, it was shown that a significant proportion of the analyte is trapped in the outermost 3 mm extremities of the tube, but only in the presence of a modifier, under normal working conditions. The same integrated absorbance sensitivity was obtained for the various modifiers studied, independent of mass up to 100-mu-g, provided that sufficiently high atomization temperatures and long integration times were employed.