Covalently modified graphitic carbon-based stationary phases for anion chromatography

Carbon-clad zirconia particles have been converted into ion-exchange media by in situ diazonium generation and thermal deposition. The surfaces prepared possess either a permanently charged anion-exchange site or a weak anion-exchange site. Surface modification optimization experiments were performed both on planar carbon surfaces and on non-porous 2 µm and porous 3 µm carbon-based particles. Modification by traditional electrochemical and thermal deposition were compared. Surface modification with the tertiary amine functionality, N,N-dimethyl-p-phenylenediamine, yielded a capacity of 6.5 µequiv./column, stable retention for >33000 column volumes and retention reproducibility of <2% RSD. A quaternary amine functionality (strong base exchanger) was achieved by reaction of the tertiary amine phase with methyl iodide. Utilizing short columns (35 × 4 mm i.d.) mixtures of common inorganic anions were separated with efficiencies of 21000 plates/m.