REFRACTORY BEHAVIOR OF LEAD IN A GRAPHITE-FURNACE WHEN PALLADIUM IS USED AS A MATRIX MODIFIER

Using platform atomization with a 0-s ramp to temperatures above 2300-2400-degrees-C, lead appears to form a refractory species in the presence of palladium and graphite. Evidence for this was the appearance of two lead absorption peaks when atomizing above 2700-degrees-C. The refractory behavior was so great that the absorbance maximum of the second lead peak occurred even after those of chromium and molybdenum atomized under the same conditions. Also, a portion of lead was retained on the platform even after ashing at 2400-degrees-C for 15 s with the inert gas flow on. Hydrogen, if present during atomization, caused an enhancement of the refractory peak. Also, the refractory peak was moro prominent when uncoated or impregnated graphite platforms, as opposed to pyrolytic ones, wore used. It is hypothesized that the refractory behavior of lead is caused by high-temperature formation of a species comprised of lead, carbon, and palladium. The refractory behavior can cause analytical errors in graphite-furnace atomic absorption spectrometry when palladium is used as a matrix modifier for lead and atomization temperatures of 2400-degrees-C or greater are used.