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A novel on-line flow injection solid phase extraction method for the preconcentration of trace toxic metals prior determination by flame atomic absorption spectrometry (FI-SPE-FAAS) was developed. The potential application of the hydrophobic reversed phase co-polymer sorbent Strata(TM)-X packed into an on-line microcolumn for the quantification of Cd(II), Pb(II), Cu(II) and Cr(VI) was demonstrated for the first time. The method was based on the on-line formation of metal complexes using sodium diethyl-dithiocarbamate (DDTC) and on the subsequent retention of them onto the sorbent material. The target analytes were completely eluted by methanol and, subsequently, directed to FAAS for quantification. All chemical and flow variables affecting the performance of the developed method were thoroughly studied and optimised. For a preconcentration time of 90s and a sampling frequency of 28h(-1), enhancement factors of 72, 140, 185, 63 and detection limits of 0.18, 1.6, 0.20 and 1.2 g L (-1) were obtained for Cd(II), Pb(II), Cu(II) and Cr(VI), respectively. The accuracy of the FI-SPE-FAAS method was evaluated by analysing certified reference materials as well as spiked environmental water samples. Furthermore, a comparative study of the analytical characteristics, the properties as well as the chemical structures of commercial polymeric based sorbent materials was employed. Strata-X sorbent was compared against Hypersep(TM) SCX, Bond Elut (R) Plexa(TM) PCX, Oasis-HLBTM and Nobias(TM) PA-1, regarding the adaptation in on-line FI-SPE-FAAS systems for metal determination, and herein presented.