It is known that monitoring of mercury and notably its species is very important to assess their impact and distribution in the environment. In this regard, the development of a methodology for mercury speciation in natural and man-made media is of particular importance. There are a variety of studies in this area associated with the application of thermal release in combination with electrothermal atomic absorption detection for direct mercury speciation in solid samples without preliminary extraction of analytes. Nevertheless, a number of issues remain that hinder its practical application as a reliable analytical method. However, in order to achieve progress in this field, it is necessary to understand the features of the evaporation process itself. The goal of this work is to study the thermal behavior of the most common mercury species in order to eliminate the gaps in this approach. At this stage, studies were carried out using pure substances and their mixtures as a starting point for a subsequent transition to real natural samples. For this the installation scheme was modernized by introducing a module that provides programmable heating of the sample and variation of the heating rate. As a result of the experiments it was shown that the transformation of studied compounds with the examples of mercury chloride, methylmercury chloride, mercury sulfide and mercury sulfate occurs under thermal exposure, which leads to a change in their physicochemical characteristics, but, nevertheless, does not prevent their baseline separation for 30 min using programmable heating mode, which includes a continuous increase in temperature with a subsequent stop until the thermal peak is formed.