A simple, compact, and powerful instrument for metal speciation in the ppt range is described. The instrument includes a HPLC module for separation and a diode laser for element-selective detection by wavelength modulation absorption spectrometry in an analytical flame. The high detection power for metal species is due to a two-beam arrangement with logarithmic amplification of the normalized signal, which compensates the laser residual amplitude modulation noise, the offset, and its fluctuation. The analytical figures of merit are demonstrated by measurements of very low concentrations of Cr(VI) in tap water.