Comprehensive study of the macropore and mesopore size distributions in polymer monoliths using complementary physical characterization techniques and liquid chromatography

Abstract

Poly(styrene-co-divinylbenzene) monolithic stationary phases with two different domain sizes were synthesized by a thermally initiated free-radical copolymerization in capillary columns. The morphology was investigated at the meso- and macroscopic level using complementary physical characterization techniques aiming at better understanding the effect of column structure on separation performance. Varying the porogenic solvent ratio yielded materials with a mode pore size of 200 nm and 1.5 μm, respectively. Subsequently, nano-liquid chromatography experiments were performed on 200 μm id × 200 mm columns using unretained markers, linking structure inhomogeneity to eddy dispersion. Although small-domain-size monoliths feature a relatively narrow macropore-size distribution, their homogeneity is compromised by the presence of a small number of large macropores, which induces a significant eddy-dispersion contribution to band broadening. The small-domain size monolith also has a relatively steep mass-transfer term, compared to a monolith containing larger globules and macropores. Structural inhomogeneity was also studied at the mesoscopic level using gas-adsorption techniques combined with the non-local-density-function-theory. This model allows to accurately determine the mesopore properties in the dry state. The styrene-based monolith with small domain size has a distinctive trimodal mesopore distribution with pores of 5, 15, and 25 nm, whereas the monolith with larger feature sizes only contains mesopores around 5 nm in size.

Selective Enrichment of Phosphorylated Peptides by Monolithic Polymers Surface Imprinted with bis-Imidazolium Moieties by UV-Initiated Cryopolymerization

“…Meso-and macropores should be formed by different processes, and the measurements of meso-and macropores are based on radically different principles. 39 The tight correlation might be related to the photopolymerization procedure, but we report this merely as an incidential observation and will refrain from discussing this further here. Based on the macroporosity, the mesopore size distribution (cf.…”

“…A somewhat surprising observation is the tight correlation (Pearson r 2 = 0.9967) seen between the average mesopore size measured by nitrogen cryosorption and the median macropore size measured by mercury intrusion porosimetry (Figure S-2), in spite of a difference in size between these pore families of nearly 100 times. Meso- and macropores should be formed by different processes, and the measurements of meso- and macropores are based on radically different principles . The tight correlation might be related to the photopolymerization procedure, but we report this merely as an incidential observation and will refrain from discussing this further here.…”

Advances and Innovations in Liquid Chromatography Stationary Phase Supports

“…Wouters et al developed a protocol combining several complementary physical characterization techniques (AFM, SEM, gas adsorption and mercury intrusion) to better understand the effect mesoand macroscopic morphology and its dependency on the polymer synthesis mixture. (101) They found that, although small-domain-size monoliths feature a relatively narrow macropore-size distribution, their homogeneity is compromised by the presence of a small number of large macropores, which induces a significant eddy-dispersion contribution to band broadening.…”

Surface-Charged Hybrid Monolithic Column for MS-Compatible Peptide Separation with High Peak Capacity and Its Application in Proteomic Analysis

“…The packed columns with a long length and small particles are beneficial in increasing peak capacity, but such columns require state-of-the-art UHPLC and column-packing instrumentation with the pressure higher than 1200 bar. , Monolithic columns, with the advantages of good permeability due to the continuous flow-through pores, offer an alternative to preparing a long column with relatively low backpressure . Silica-based monoliths possess a unique macro-mesopore structure with the advantages of an adjustable pore size, − a relatively homogeneous structure, , and a high column efficiency . Thus, they are widely used in peptide separation.…”

“…5,6 Monolithic columns, with the advantages of good permeability due to the continuous flow-through pores, offer an alternative to preparing a long column with relatively low backpressure. 7 Silica-based monoliths possess a unique macro-mesopore structure with the advantages of an adjustable pore size, 8−10 a relatively homogeneous structure, 8,11 and a high column efficiency. 12 Thus, they are widely used in peptide separation.…”