On-column electrochemical redox derivatization for enhancement of separation selectivity of liquid chromatography: Use of redox reaction as secondary chemical equilibrium

An on-column electrochemical redox derivatization for enhancement of high-performance liquid chromatography (HPLC) separation selectivity is presented using electrochemically modulated liquid chromatography (EMLC) and porous graphitic carbon (PGC) as the packing material. PGC therefore serves two purposes: it acts both as a chromatographic stationary phase and as a working electrode. The capability of on-column electrochemical redox derivatization was evaluated using hydroquinone and catechol as model compounds. By manipulation of the applied potential, hydroquinone and catechol will migrate as equilibrium mixtures, hydroquinone and p-benzoquinone and catechol and o-benzoquinone in the potential region of 25–125 mV and 150–200 mV (vs. Ag/AgCl), respectively. These redox reactions can be used as secondary chemical equilibria so that the corresponding equilibrium mixtures elute as single peaks and their retention times can be controlled by alterations in the potential applied to the PGC stationary phase. Homogeneity of the redox activity of the PGC stationary phase applied potential was also demonstrated.