Under certain exptl. conditions-short pyrolysis times, fast heating rates and presence of reducing agent-increasing vaporization temps. led to decreasing losses of Pd as the initial mass was increased between 0.3 and 5.0 ng. When Pd is introduced into the tube at mg levels, as is typical for modifiers, no similar tendency was established and max. loss-free temps. approach 1300 Deg. A procedure for deriving the enthalpy of vaporization was developed which characterizes low-temp. Pd release during pyrolysis. The evaluated enthalpy of vaporization increases with increasing Pd mass at ng levels. This could be explained by the enhancement of the dimensions of the vaporized particles/droplets. Because of the small mass of the injected sample, the particles obtained are sufficiently small and the behavior of the droplets at higher pyrolysis temps. could be explained by the Kelvin equation. In such a case the variation of the particle size leads to variation in their vapor pressure and, as a result, the enthalpy of vaporization is changed. At mg levels the Pd particles obtained are sufficiently large and the vapor pressure and enthalpy of vaporization are not a function of the particle size. Variation of the initial mass of Pd does not influence the shape of pyrolysis curves when longer pretreatment times were used. The prolonged pyrolysis times possibly influence the rates of nucleation and crystal growth and favor the diffusion of Pd into and on to the graphite surface, thus the initial sample distribution is changed. [on SciFinder (R)]