An intracavity laser spectrometer equipped with a graphite furnace electrothermal atomizer and two alternative types of narrow atomic lines detection schemes (high resolution diffraction spectrograph with optical multichannel analyzer or a resonant detector based on a hollow-cathode lamp) is described. Such system was used to determine ultra-trace amounts of lithium and strontium in aqueous solutions. A significant reduction in the measurable absorbance was demonstrated for both elements. Careful optimization of the operating conditions of the detection systems and a comparison of their typical features and advantages were performed.