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

Abstract

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%.

Performance of graphene sheets as stationary phase for capillary gas chromatographic separations

“…However, the high affinity of graphene as stationary phase for aromatics seems not quite favorable for its chromatographic separation of the analytes. As reported, graphene as stationary phase in LC and CEC exhibited severe peak tailings and poor resolution for some aromatics such as naphathelene, biphenyls, alkyl benzenes, PAEs and nitroanilines [25][26][27].…”

“…The reduction can be performed through hydrothermal reduction [12,13], chemical reduction [14] and so forth. Recently, graphene has been reported in separation science as adsorption material for sample preparation [15][16][17][18][19][20][21][22][23][24] and as stationary phase for liquid chromatography (LC) [25,26] and capillary electrochromatography (CEC) [25,27].…”

Recent advances in column coatings for capillary electrophoresis of proteins

“…Carbon nanomaterials are mainly immobilized onto the capillary surface via covalent bonding [63,66,69]. Bonn and coworkers prepared a chemical capillary coating with fullerenol (derivatized fullerene) covalently bonded to silanized capillary surface [63].…”

“…The coated capillary showed great stability in the pH range of 2.0 to 10.0 and high separation performance were obtained in the analysis of a tryptic digest of five proteins with good reproducibility. Qu et al applied a covalently coated capillary with graphene oxide and obtained good separation of five chicken egg white proteins [66]. Chi and coworkers used photosensitive diazoresin (DR) as coupling agent to covalently link carboxyl-fullerene to the inner capillary surface [69].…”

Tunable thick porous silica coating fabricated by multilayer-by-multilayer bonding of silica nanoparticles for open-tubular capillary chromatographic separation

“…Compared to other materials, nanoparticles have the merits of large surface area and ease of preparation. Therefore, nanoparticles of silica [30], gold [26,[31][32][33][34][35], titanium dioxide [36][37][38], and grapheme oxide nanosheets [39][40][41] have been immobilized onto the inner surface of capillary column. However, although these types of nanoparticles have been used successfully for chromatographic separation, in most cases, columns were coated with only a single layer.…”