The invention relates to analytical chemistry. In the analyser, mercury placed in a spectral lamp is enriched with a mercury isotope having an even neutron number, wherein said isotope constitutes not less than 50% of the total mercury content in the spectral lamp. Moreover, the discharge cavity of the spectral lamp is connected to a ballast cavity, the volume of which is greater than the discharge cavity volume, and electrical discharge generating means, the discharge cavity and the ballast cavity are designed in such a way that the discharge generated in the discharge cavity does not penetrates into the ballast cavity. A buffer gas in the spectral lamp contains a noble gas in a quantity equal to or greater than 50%, the charge of the atomic core of said gas being not less than 36. Said invention makes it possible to lower the detection level of mercury in a carrier gas and to reduce a drift.