A study using a combination of thermogravimetric and x-ray diffraction analyses has shown that a solution of hexachloroplatinic acid (H^tClJ, usually used as a standard in atomic absorption spectrophotometric (AAS) measurements, was broken down to yield volatile PtCl2 before being converted to metallic platinum. On the other hand, a solution ofcis-diaminodichloroplatinum(II) (cis-Pt(NH')2Cl2; cis-DDP) was converted to metallic platinum in a single step. The differences in their thermal decomposition mechanisms could be one of the reasons as to why carbon furnace atomic absorption spectrophotometric (CFAAS) signal from H^tCl^ was found to be lower than that of cis-DDP in aqueous solution.