Microfluidic Precision Manufacture of High Performance Liquid Chromatographic Microspheres

A key bottleneck in developing chromatographic material is the chemically entangled control of morphology, pore structure, and material chemistry, which holds back precision material manufacture in order to pursue advanced separation performance. In this work, a precision manufacture strategy based on droplet microfluidics was developed, for production of highly efficient chromatographic microspheres with independent control over particle morphology, pore structure and material chemistry. The droplet-synthesized microspheres display extremely narrow particle size distribution (CV<3 %), enabling a 100 % production yield due to complete elimination of sieving steps. More importantly, the size of the droplet-synthesized microspheres is freely adjustable without the need for re-optimizing chemical recipes or reaction conditions. The resulting materials exhibit excellent separation efficiencies, achieving a reduced plate height of hmin=1.67. This precision manufacture strategy also allows for flexible pore design and continuous pore size adjustment across three orders of magnitudes, providing a novel vehicle for resolution fine-tuning targeting protein separation. Besides traditional silica, organic-inorganic hybrid silica, zirconia, and titania microspheres can also be precisely synthesized on the same platform, supporting various separation applications and operating conditions. Powered by precision manufacture, super-throughput production, and versatile chemistry, the high-performance droplet-synthesized separation material will pave the way towards green and precision chromatographic industry.

Liquid chromatographic enantiomer separations applying chiral ion-exchangers based on Cinchona alkaloids

As the understanding of the various biological actions of compounds with different stereochemistry has grown, the necessity to develop methods for the analytical qualification and quantification of chiral products has become particularly important. The last quarter of the century has seen a vast growth of diverse chiral technologies, including stereocontrolled synthesis and enantioselective separation and analysis concepts. By the introduction of covalently bonded silica-based chiral stationary phases (CSPs), the so-called direct liquid chromatographic (LC) methods of enantiomer separation became the state-of-the-art methodology. Although a large number of CSPs is available nowadays, the design and development of new chiral selectors and CSPs are still needed since it is obvious that in practice one needs a good portfolio of different CSPs and focused "chiral columns" to tackle the challenging tasks. This review discusses and summarizes direct enantiomer separations of chiral acids and ampholytes applying anionic and zwitterionic ion-exchangers derived from Cinchona alkaloids with emphasis on literature data published in the last 10 years. Our aim is to provide an overview of practical solutions, while focusing on the integration of molecular recognition and methodological variables.

Chemoaffinity material for plasmid DNA analysis by high-performance liquid chromatography with condition-dependent switching between isoform and topoisomer selectivity

Plasmid DNA may exist in three isoforms, the linear, open-circular (oc, "nicked"), and covalently closed circular (ccc, "supercoiled") form. We have recently reported on the chromatographic separation of supercoiled plasmid topoisomers on cinchona-alkaloid modified silica-based stationary phases. Herein, we present a selectivity switching mechanism to achieve separation of isoforms and/or supercoiled topoisomers using the very same chromatographic column and system. While salt gradient elution facilitates topoisomer separation, the supercoiled species are eluting as a single peak upon elution by a mixed pH and organic modifier gradient, still well separated from the other isoforms. We have found that a mobile phase pH value near the pI of the zwitterionic adsorbent surface leads to full recovery of all plasmid DNA isoforms, which is a major issue when using anion exchange-based resins. Furthermore, the observed elution pattern, oc < linear < ccc, is constant upon changes of mobile phase composition, gradient slope, and plasmid size. The remarkable isoform selectivity found on quinine-based selectors is explained by van't Hoff plots, revealing a different binding mechanism between the supercoiled plasmid on one hand and the oc and linear isoforms on the other hand.