Electrochromatographic performance of graphene and graphene oxide modified silica particles packed capillary columns.

Graphene oxide functionalized silica microspheres (GO@SiO2 ) were synthesized based on condensation reaction between amino from aminosilica particles and carboxyl groups from GO. Reduction of GO@SiO2 with hydrazinium hydroxide generated graphene modified silica particles (G@SiO2 ). GO@SiO2 and G@SiO2 packed capillary columns for capillary electrochromatography were thereafter fabricated by pressure slurry packing with single-particle frits. GO of 0.3 mg/mL in dispersion solution for GO@SiO2 synthesis was considered as a compromise between retaining and column efficiency whereas GO@SiO2 of 20 mg/mL in slurries for column packing was chosen for a homogenous and tight bed. Optimum mobile phases were acquired considering both electroosmotic flow and resolution at an applied voltage of -6 kV as the following: acetonitrile/phosphate buffer (10 mM, pH 7.0), 75:25 (v/v) for polycyclic aromatic hydrocarbons and 50:50 (v/v) for aromatic compounds. A comparison was made between electrochromatographic performances for three PAHs (naphthalene, fluorene and phenanthrene) and three aromatic compounds of various polarities (toluene, aniline and phenol) on bare aminosilica, GO@SiO2 and G@SiO2 packed columns, which proved the contribution of alone or combinational actions of solvophobic effect and π-π electron stacking as well as hydrogen bonds to retaining behaviors by GO@SiO2 and G@SiO2 . Well over-run, over-day and over-column precisions (retention time: 0.3-1.4, 1.1-3.8 and 2.8-5.2%, respectively; peak area: 2.6-6.5, 4.8-8.3 and 6.5-12.6%, respectively) of GO@SiO2 packed columns were a powerful proof for good reproducibility. Analytical characteristics of GO@SiO2 packed capillary columns in CEC analysis of fresh water were evaluated with respect to linearity (R2 = 0.9961-0.9989) over the range 0.1 to 100 mg/L and detection limits of 9.5 for naphthalene, 12.6 for fluorene and 16.2 μg/L for phenanthrene. Further application to fresh water increased the visibility of the proposed material, where good spike recoveries in the range 89-96% were offered.