Sub-second liquid chromatography in very short packed beds is demonstrated as a broad proof of concept for chiral, achiral, and HILIC separations of biologically important molecules. Superficially porous particles (SPP, 2.7 μm) of different surface chemistries, namely, teicoplanin, cyclofructan, silica, and quinine, were packed in 0.5-cm-long columns for separating different classes of compounds. Several issues must be addressed to obtain the maximum performance of 0.5 cm columns with reduced plate heights of 2.6 to 3.0. Modified UHPLC hardware can be used to obtain sub-second separations provided extra-column dispersion is minimized and sufficient data acquisition rates are used. Further, hardware improvements will be needed to take full advantage of faster separations. The utility of power transform, which is already employed in certain chromatography detectors, is shown to be advantageous for sub-second chromatography. This approach could prove to be beneficial in fast screening and two-dimensional liquid chromatography.
New stationary phases are continuously developed for achieving higher efficiencies and unique selectivities. The performance of any new phase can only be assessed when the columns are effectively packed under high pressure to achieve a stable bed. The science of packing columns with stationary phases is one of the most crucial steps to achieve consistent and reproducible high-resolution separations. A poorly packed column can produce non-Gaussian peak shapes and lower detection sensitivities. Given the ever larger number of stationary phases, it is impossible to arrive at a single successful approach. The column packing process can be treated as science whose unified principles remain true regardless of the stationary phase chemistry. Phenomenologically, the column packing process can be considered as a constant pressure or constant flow high-pressure filtration of a suspension inside a column with a frit at the end. This process is dependent on the non-Newtonian suspension rheology of the slurry in which the particles are dispersed. This perspective lays out the basic principles and presents examples for researchers engaged in stationary phase development. This perspective provides an extensive set of slurry solvents, hardware designs, and a flowchart, a logical approach to optimal column packing, thus eliminating the trial and error approach commonly practiced today. In general, nonaggregating but high slurry concentrations of stationary phases tend to produce well packed analytical columns with small particles. Conversely, C18 packed capillary columns are best packed using agglomerating solvents.
Geopolymers belong to an interesting class of X-ray amorphous polycondensed aluminosilicate ceramic solids. The high mechanical strength, chemical stability in basic conditions, and water insolubility make geopolymers a unique solid support in separation science. This work describes a new straightforward synthetic procedure for making spherical porous geopolymer particles with high surface area which are amenable for chromatographic purposes. In-depth physicochemical evaluation of geopolymers is conducted via particle size distribution, porosity measurements, X-ray diffraction, pH titration, and energy-dispersive spectroscopy and compared with silica, titania, and zirconia. Chromatographic selectivity shows that the surface chemistry of geopolymers has strong hydrophilic and electrostatic character, which makes it different from 36 chromatographic columns. Hydrophilic interaction liquid chromatography in columns packed with geopolymer particles shows different selectivity than that in silica columns, with excellent peak shapes. Phosphate or fluoride additives are not required as they are for zirconia or titania phase.
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