An atomic absorption spectrometer for measuring mercury concentration in a sample which includes an arrangement for producing emission lines of 184.9 and 253.7 nm at the same time, a sample accommodating chamber which can be irradiated with radiation of the emission lines, two electro-optical transducers responsive, with different sensitivities, to the radiation emission lines and arranged so that radiation passing through the sample chamber simultaneously impinges thereon, each extinction measuring means having a preselected extinction value range, and a comparator for switching between respective measurement ranges to determine the mercury concentration.