Redox Derivatization Chromatography

On-column and on-line redox derivatization methods were developed for enhancing the separation selectivity of HPLC for the analysis of oxidizable and reduciable compounds. On-column derivatization is assisted by the redox activity of a stationary phase packing material such as porous graphitic carbon (PGC) or electrochemically manipulated using an electrochemically modulated liquid chromatographic technique. The analyte compound migrates in the column as a single zone of a mixture of oxidized and reduced forms, so that the retention of the compound is determined by the relative concentrations of the two forms in the column. On the other hand, the on-line redox derivatization system consists of two separation columns and one redox derivatization unit placed between them. The redox reaction proceeds rapidly in the derivatization unit, so that the analyte compound migrates as its original faun in the first column, while as its oxidized or reduced form in the second column. The retention of the analytes is thus controlled by the lengths of the two separation columns in this system. A two-dimensional on-line redox derivatization HPLC system was also developed where "heart-cutting" chromatography, in conjunction with on-line redox derivatizaion, was used. This system enables one to isolate specific analytes in complex matrix samples. We have demonstrated that the on-column and on-line redox derivatization methods using porous graphitic carbon as a catalytic redox agent allows the selective separation and determination of cobalt in a manganese nodule and a stainless-steel sample without the interference of metal components coexisting at high concentrations. This technique may find applications in analysis not only of inorganic compounds, such as metal ions, but also of organic or biomolecules.