BEHAVIOR OF THE SYSTEM - LEAD-SODIUM-CHLORIDE IONS PALLADIUM DURING ATOMIZATION IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

It was found that the interference effect of chlorides at the lead det ermination by GF AAS depends on the properties of the chlorides and on the medium in which the sample is dissolved. In nitric acid solution one observes mainly the effects of cations contained in the chlorides. In hydrochloric acid or in a mixed nitric-hydrochloric acid medium th e observed effects are due to the type of chlorides. The chlorides, wh ich have a decomposition temperature higher than the used pyrolysis (c harring) temperature, inhibit the reduction of lead chloride to the me tal form and enable its losses by evaporation. Other chlorides, which decompose below the pyrolysis temperature, evolve free chlorine atoms and those form very volatile lead-chlorine compound evaporating alread y at about 200-degrees-C. Palladium acts properly as modifier only in nitric acid solution. In the presence of a large excess of chloride io ns, particularly in the hydrochloric acid medium, it is transformed, a t least partially, into the form of thermally unstable chloride which causes the losses of lead during pyrolysis and, consequently, causes a strong suppression of the measured signal. The explanation of the mec hanism of all processes occurring in the graphite tube for the analyti cal system to be discussed has been proposed.