The interferences of sodium chloride with the determination of a volatile (zinc) and a low volatility (cobalt) element by graphite furnace atomic absorption spectrometry (GFAAS) were examined. For various masses of the sodium chloride, the effects of pretreatment temperature and time, and heating rate on the atomization of the analyte were investigated using a specially designed dual cavity platform, which in principle allows the analyte and the interferent to vaporize from the separate cavities so that gas and condensed phase interferences can be distinguished to some extent. In addition, background and atomic absorption signals obtained in the pretreatment step provided very important information to clarify the interference mechanisms. In the presence of sodium chloride, formation of a highly volatile zinc chloride contributes mainly to the losses of zinc, especially during high pretreatment temperatures. The losses of zinc and cobalt can partly be attributed to the occlusion of the analytes in microcrystals of the interferent and some of these are thrown from the furnace without decomposing early in the atomization step or during the pretreatment step. In addition, expulsion of both analytes together with the violently expanding matrix gases seems to be a likely interference mechanism as well.