3-Dimensional X-ray microtomography methodology for characterization of monolithic stationary phases and columns for capillary liquid chromatography - A tutorial

Liquid chromatography, a key tool for the advancement of single-cell omics analysis

Single-cell analysis can allow for an in-depth understanding of diseases, diagnostics, and aid the development of therapeutics. However, single-cell analysis is challenging, as samples are both extremely limited in size and complex. But the concept is gaining promise, much due to novel sample preparation approaches and the ever-improving field of mass spectrometry. The mass spectrometer's output is often linked to the preceding compound separation step, typically being liquid chromatography (LC). In this review, we focus on LC's role in single-cell omics. Particle-packed nano LC columns (typically 50-100 μm inner diameter) have traditionally been the tool of choice for limited samples, and are also used for single cells. Several commercial products and systems are emerging with single cells in mind, featuring particle-packed columns or miniaturized pillar array systems. In addition, columns with inner diameters as narrow as 2 μm are being explored to maximize sensitivity. Hence, LC column down-scaling is a key focus in single-cell analysis. But narrow columns are associated with considerable technical challenges, while single cell analysis may be expected to become a "routine" service, requiring higher degrees of robustness and throughput. These challenges and expectations will increase the need and attention for the development (and even the reinvention) of alternative nano LC column formats. Therefore, monolith columns and even open tubular columns may finally find their "killer-application" in single cell analysis.

Facile synthesis of zirconia-coated mesoporous silica particles by hydrothermal strategy under low potential of hydrogen conditions and functionalization with dodecylphosphonic acid for high-performance liquid chromatography

In this work, multilayer zirconia-coated silica (ZrO₂/SiO₂-n) microspheres were successfully produced by a straightforward hydrothermal procedure with a low concentration of Zr⁴⁺ (5 mM) under low potential of hydrogen (pH) conditions (pH = =2). The obtained ZrO₂/SiO₂-n materials exhibited favorable characteristics for high-performance liquid chromatography (HPLC) separation, including high surface area and pore volume, good pore structure, narrow particle size, and pore size distribution. In addition, the zirconia coverage in the mesopores was confirmed by soaking the material in 1 M NaOH solution, with the particles showing strong resistance to the basic solution. The obtained ZrO₂/SiO₂-n stationary phases were packed into a fused-silica capillary tubing for the separation of alkaloids in hydrophilic interaction chromatography (HILIC) mode, and a column efficiency of 47,800 plates/m was obtained for berberine on a ZrO₂/SiO₂-6 micro column. The ZrO₂/SiO₂-6 microspheres were further modified by dodecylphosphonic acid (C₁₂P-2-ZrO₂/SiO₂-6); the C₁₂P-2-ZrO₂/SiO₂-6 material showed great potential for application in reversed-phase liquid chromatography (RPLC) mode. The C₁₂P-2-ZrO₂/SiO₂-6 micro column showed a column efficiency of 55,000 plates/m for naphthalene and 51,300 plates/m for benzene.