Effect of palladium modifier on the analyte vapor transport in a graphite furnace atomizer

The effect of Pd modifier on vapor transport of In, Ga, Mn, Ph and Sn in a graphite furnace atomizer was investigated using a Quant-ZETA atomic absorp tion spectrometer. The fast heating of the furnace (ramp time 0.15-0.25 s) followed by temperature stabilization at 2500-2800 K enabled us to measure the vapor dissipation rate using the 'tails' of the atomic absorption signa ls. The analyte, 0.02-0.5 ng, was vaporized alone or together with Pd. Pd w as introduced and thermally treated before the sampling of the analyte. Sma ll amounts of Pd (0.1 mug) significantly changed the vaporization pattern a nd residence time of the atomic vapors, but affected the peak area only sli ghtly. In this case, the vapor removal is 1.5-1.8 times slower than that pr edicted by theory for the diffusion mechanism of vapor release. The involve ment of vapor adsorption by the wall and molecular diffusion in the vapor t ransport is suggested. The increase of Pd amount (up to 2.5 mug) causes the gradual reduction of residence time and peak area, due to the increase of diffusion rate of atomic vapor. Using the two-line method of temperature me asurement, it is shown that this effect is accompanied by a temperature inc rease of 75-200 K, when 0.5-4 mug Pd are vaporized. The hypothesis is advan ced about an exothermal interaction of Pd vapor with graphite. The variatio ns of atom residence time in the furnace are discussed as practical limitat ions of the theory of absolute analysis. (C) 2001 Elsevier Science B.V. All rights reserved.