An alternative thermodiffusion interface (TDI) was designed and constructed for the effective online coupling of capillary gas chromatography (cGC) and inductively coupled plasma mass spectrometry (ICPMS). Pb(2+), (CH3)3Pb(+), (C2H5)3Pb(+), Hg(2+), CH3Hg(+) and C2H5Hg(+) were derived as Pb(C4H9)4, (CH3)3PbC4H9, (C2H5)3PbC4H9, (C4H9)2Hg, CH3HgC4H9, and C2H5HgC4H9 when butyl magnesium bromide was employed as a derivatization reagent for a proof-of-concept study, avoiding the loss of their species specific information. All these derivatives together with the neutral fully saturated (CH3)4Pb and (C2H5)4Pb could be quantitatively separated within 7 min using a 15 m long capillary column, allowing the determination and speciation of organic and inorganic Pb and Hg species in a single run. The method detection limits (3sigma) for Me4Pb, Et4Pb, Me3Pb(3+), Pb(2+), MeHg(+), EtHg(+), and Hg(2+) are 0.07, 0.06, 0.04, 7.0, 0.09, 0.1, and 0.2 pg g(-1), respectively. Moreover, tri-n-propyl-lead chloride was synthesized and used as an alternative internal standard for the accurate and simultaneous speciation analysis of Pb and Hg in complicated environmental and biological samples for the first time. This cGC-TDI-ICPMS method was validated by analyzing Pb and Hg species in certified reference materials and then was applied to simultaneous speciation analysis of Pb and Hg in real-life samples. It is expected that these approaches can be extended to the speciation of other organometallic compounds after suitable modifications and so will aid in monitoring the occurrence, pathways, toxicity, and/or biological effects of these compounds in the environment and in organisms.