Homogeneous Edge-Plane Carbon as Stationary Phase for Reversed-Phase Liquid Chromatography

Carbon stationary phases have been widely used in HPLC due to their unique selectivity and high stability. Amorphous carbon as a stationary phase has at least two sites of interaction with analytes: basal-plane and edge-plane carbon sites. The polarity and adsorptivity of the two sites are different. In this work, the edge-plane carbon stationary phase is prepared by surface-directed liquid crystal assembly. Specific precursor polymers form discotic liquid crystal phases during the pyrolysis process. By using silica as the substrate to align the discotic liquid crystal, edge-plane carbon surfaces were formed. Similar efficiencies as observed for Hypercarb were observed in chromatograms. The column efficiency was studied as a function of linear flow rate. A minimum reduced plate height of 6 was observed in these studies. To evaluate the performance of the homogeneous edge-plane carbon stationary phase, linear solvation energy relationships were used to compare these ordered carbon surfaces to commercially available carbon stationary phases, including Hypercarb. Reversed-phase separations of nucleosides, nucleotides, and amino acids and derivatives were demonstrated using the ordered carbon surfaces, respectively. The column batch-to-batch reproducibility was also evaluated. The retention times for the analytes were reproducible within 1–6% depending on the analyte

Planar Electrochromatography Using an Electrospun Polymer Nanofiber Layer

Electrospun polymer nanofiber stationary phases were examined for their application to planar electro­chromatography (PEC). Separations were performed on polyacrylo­nitrile nanofiber ultra-thin-layer chromatography (UTLC) plates in 1–2 min using a ternary mobile phase. The influences of buffer concentration and pH, ratio of organic modifier, and development time on analyte migration distances were studied. Band broadening in this system was studied as a function of distance. The plate height initially decreased and then plateaued with a minimum plate height value as low as 11 μm. Nanofiber alignment considerably increased analyte migration rate, but larger spot sizes were noted when nearly complete fiber alignment was used. The easily tunable stationary phase thickness can be tailored to a given separation, where thinner layers promote faster separations and thicker layers are ideal for more complex mixtures. Compared to UTLC, PEC offers unique selectivity and decreased analysis time (>4 times faster over 15 mm). Results for a two-dimensional separation using UTLC and PEC are also reported. These rapid separations required 11 min using a 40 × 40 mm plate and exhibited a significant increase in separation number (70–77)