Morphology optimization and assessment of the performance limits of high-porosity nanostructured polymer monolithic capillary columns for proteomics analysis
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This study targets the synthesis of high external-porosity poly(styrene-co-divinylbenzene) monolithic support structures with macropore and globule sizes in the sub-micron range, aiming at the realization of high-speed and high-resolution gradient separations of intact proteins and peptides. The thermodynamic and kinetic aspects of the free-radical polymerization synthesis were adjusted by tuning the porogen to monomer ratio, the porogen ratio, the initiator content, and polymerization temperature. Next, column morphology was linked to eddy-dispersion and mobile-phase mass-transfer contributions and the chromatographic performance limits were benchmarked against conventional packed columns and silica monoliths. Polymer monolithic structures yielding a separation impedance as low as 976 were created allowing to generate N > 1,000,000 (for an unretained marker), albeit the expense of very long analysis times. Decreasing the macropore and globule sizes below a certain threshold led to significant increase in eddy dispersion, as globular entities agglomerate, and a small number of large flow-through pores permeate the overall fine interconnected polymer network with small diameter flow-through pores. The potential of monolith chromatography for proteomics application is demonstrated with a ballistic 6 s gradient separation of intact proteins and a high-resolution nanoLC-Orbitrap mass spectrometric analysis of a tryptic E. coli digest applying a coupled-column system.