Determination of Trace Amount of Cobalt in a Steel Sample by Two-dimensional On-line Redox Derivatization Liquid Chromatography

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A two-dimensional on-line redox derivatization HPLC system was developed where “heart-cutting” chromatography, in conjunction with on-line redox derivatizaion, was used to isolate specific analytes in complex matrix samples. Cobalt in a stainless steel sample was used as a model analyte to evaluate the performance of the HPLC system developed. We adopted a small column packed with porous graphitic carbon (PGC) treated with hydrogen peroxide as an oxidation derivatization unit and two C18 silica columns which had adsorbed hexadecyltrimethylammonium ion as the first and second separation columns. After complexation of metal components with ethylenediaminetetraacetate (edta), the sample was directly submitted to the analysis by the HPLC system without any preseparation steps. In the first dimension separation cobalt was eluted as Co(II)-edta and was separated from trivalent metal complexes such as Fe(III) and Cr(III), while it was selectively oxidized to Co(III)-edta in the PGC column and then completely separated from the divalent metal complexes such as Ni(II) on the second column. A successful application of this method to accurate and precise determination of trace amount of cobalt in a stainless steel is demonstrated.