A simple capillary flow porometer (CFP) was assembled for pore structure characterization of monolithic capillary liquid chromatography columns based on ASTM standard F316-86. Determination of differential pressures and flow rates through dry and wet samples provided the necessary information to determine the through-pore throat diameter, bubble point pore diameter, mean flow pore diameter, and pore distribution. Unlike measurements in bulk using traditional techniques to provide indirect information about the pore properties of monolithic columns, monoliths can be characterized in their original chromatographic forms with this system. The performance of the new CFP was first evaluated by characterizing the pore size distributions of capillary columns packed with 3, 5, and 7 µm spherical silica particles. The mean through-pore diameters of the three packed columns were measured to be 0.5, 1.0 and 1.4 µm, which are all smaller than the pore diameters calculated from a close-packed arrangement (i.e., 0.7, 1.1 and 1.6 µm), with distributions ranging from 0.1 - 0.7, 0.3 - 1.1 and 0.4 - 2.6 µm, respectively. This is reasonable, since visual inspection of SEM images of the particles showed relatively large fractions of smaller than specified particles in the samples. Typical silica monoliths were fabricated via phase separation by polymerization of tetramethoxysilane (TMOS) in the presence of poly(ethylene glycol) (PEG). The mean pore diameter and pore size distribution measured using the CFP system verified that a greater number of pores with small throat diameters were prepared in columns with higher PEG content in the prepolymer mixture. SEM images also showed that the pore diameters of monoliths fabricated in bulk were found to be smaller than those in monoliths synthesized by the same procedure, but confined in capillary tubes. The CFP system was also used to study the effects of column inner diameter and length on pore properties of polymeric monoliths. Typical monoliths based on butyl methacrylate (BMA) and poly(ethylene glycol) diacrylate (PEGDA) in capillary columns with different inner diameters (i.e., 50 to 250 µm) and lengths (i.e., 1.5 to 3.0 cm) were characterized. The mean pore diameters and the pore size distributions indicated that varying the inner diameter and/or the length of the column affected little the pore properties. The latter finding is especially important to substantiate the use of CFP for determination of monolithic pore structures in capillaries. The results indicate that the through-pores are highly interconnected and, therefore, pore structure determinations by CFP are independent of capillary length. A negatively charged polymer monolith based on BMA, ethylene glycol dimethacrylate (EDMA) and 2-acryloylamido-2-methylpropanesulfonic acid monomer (AMPS), was successfully prepared in silica sacrificial layer, planar (SLP) microchannels. Extraction of FITC (fluorescein 5-isothiocyanate) labeled phenylalanine and capillary electrochromatography (CEC) of FITC labeled glycine using this monolithic stationary phase were demonstrated.

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Characterization of the pore structure is a crucial part in themanufacturing of porous media used for purification of biologicalpharmaceuticals. This project took place at Cytiva in Uppsala and aimedat optimizing a newly developed method in pore structurecharacterization called size-exclusion quantification NMR (SEQ-NMR). Bymeasuring with diffusion NMR on a polymer solution before and afterequilibration with a material of interest the pore structure of thematerial can be determined. This project aimed at reducing the durationof a SEQ-NMR experiment while examining the performance of the methodduring different conditions with the goal of making the methodapplicable for quality control procedures. The method was optimizedboth by simulations and by experimental diffusion NMR measurements. Itwas discovered that the performance of the method could be improved byhaving an optimal mixture of the polymer solution and duringexperiments distributing ten measurement points with linear spacing.With these parameters optimized the duration of the method could bereduced with 22 hours landing on a total duration of 8 hours. Theduration combined with the complexity of the method still makes themethod unsuitable for use in quality control of porous media. Despitethe small possibility of SEQ-NMR being a quality control method thisproject has proven the method to be both reproducible and sensitive.