Capillary Coated with Graphene and Graphene Oxide Sheets as Stationary Phase for Capillary Electrochromatography and Capillary Liquid Chromatography

Graphene oxide (GO) nanosheets were immobilized onto the capillary wall using 3-aminopropyldiethoxymethyl silane as coupling agent. Graphene coated column (G@column) was fabricated by hydrazine reduction of GO modified column. Scanning electron microscopy (SEM) images provided visible evidence of the GO grafted on the capillary wall. Energy dispersive X-ray spectrometry (EDS) indicated the high coverage of the GO on the capillary wall. The G@column exhibited a pH-dependent electroosmotic flow (EOF) from anode to cathode in the pH range of 3–9 while the graphene oxide coated column (GO@column) showed a constant EOF. Both GO@column and G@column were evaluated for open-tubular capillary electrochromatography (OT-CEC). The GO@column was also evaluated for open-tubular capillary liquid chromatography (OT-CLC). Good separation of the tested neutral analytes on the GO@column was achieved on the basis of a typical reversed-phase behavior. On the contrary, G@column showed poor separation performance because of the strong π–π stacking and hydrophobic interactions between graphene and polyaromatic hydrocarbons. The high coverage of GO improved the column phase ratio which makes the GO@column promising for OT-CLC separation. Five of the major known proteins including three glycoisoforms of ovalbumin in chicken egg white were identified in a single run on the GO@column with phosphate buffer (5 mM, pH 7.0) and an applied voltage of 20 kV. The run-to-run, day-to-day, and column-to-column reproducibilities are evaluated by calculating the relative standard deviations (RSDs) of the EOF in OT-CEC and retention time of naphthalene in OT-CLC, respectively. These RSD values were found to be less than 3%.