The interference of nickel chloride on the determination of copper by electrothermal atomic absorption spectrometry was investigated using a specially designed dual cavity platform (DCP), which allows the analyte and interferent to vaporize from separate cavities, so that gas and condensed phase interferences can be distinguished to some extent. It was found that, when low pyrolysis temperatures were used, the interference of nickel chloride on copper originated from the formation of copper chloride in the condensed phase, which is not efficiently dissociated in the atomization stage. Alternately, when analyte and interferent were in separate cavities of the DCP, a gas-phase reaction between copper and chlorine in the atornization stage resulted in a similar signal depression. When higher pyrolysis temperatures were used, interference could be. attributed to losses of volatile copper chloride in the pyrolysis stage. These losses were more pronounced when analyte and interterent were in separate cavities of the DCP, indicating again a gas-phase reaction between copper and chlorine, as well as a protective action of nickel oxide, when analyte and interferent were mixed. Colloidal palladium used as modifier removed the chloride interference independent of the pyrolysis temperature applied, when copper and nickel chloride were mixed. Colloidal palladium also increased the integrated absorbance for copper by 40-50%, even when analyte and modifier were in separate cavities of the DCP, indicating a strong gas-phase interaction between copper atoms and the modifier through adsorption/desorption processes. (c) 2005 Elsevier B.V All rights reserved.