Application of an in-situ Thermo-polymerized Porous Polymer: Creation of an On-column Frit for a Packed Capillary HPLC Column

Abstract

Capillary high-performance liquid chromatography (capillary HPLC), [1][2][3][4] as an intermediate technique between conventional liquid chromatography and microchip separations, has been one of the main trends as a separation technique during the past decade.Especially, the development of proteomics and metabolomics has promoted the rapid development of capillary HPLC technology in recent years. Using capillary HPLC columns (typical size, 0.32 -0.075 mm i.d.) has many advantages over using a common HPLC column (4.6 mm i.d.). Miniaturization of the separation column has led to lower running costs and reduced environmental pollution by solvents and chemicals. For example, a reduction of the column i.d. from 4.6 to 0.32 mm allows the same analysis with more than 200-times less solvent as the mobile phase. On the other hand, capillary HPLC has low sample-volume requirements and easy connection to mass spectrometry (MS). These advantages are paid more attention in the field of life sciences, since bioanalytical applications are often sample-limited. Nowadays, capillary HPLC coupled with MS as a complementary method for two dimensional polyacrylamide gel electrophoresis has become an important tool for separating protein. [5][6][7] However, the front-end column technology need to be further improved.To date, there are mainly two kinds of capillary HPLC columns used. One is a packed column, typically filled with alkylated silica particles in fused-silica capillaries. The other is a monolithic column, 8,9 which is prepared by in-situ polymerization and avoids frit fabrication. Although monolithic capillary columns are prepared much more easily than packed capillary columns, packed capillary columns are mainly employed in proteomics research because of the availability of various packing materials. However, the packing of micronsized particles into a capillary tubing and the preparation of solid and stable on-column frits at the end of the columns are difficult techniques.Usually a capillary column needs tubing at the end of the column for connecting with the detector. The packed bed and the tubing for the detector are connected with a union or by glue. However, the connection can inevitably induce a dead volume. Considering the detrimental influence of the dead volume, the best design for the column is a zero dead volume connection between the packing bed and the tubing for the detector. If the packed bed and the tubing for the detector are integrated in one capillary, the detection window can be made very close to the frit, so as to obtain the minimum dead volume. In order to retain the packing material inside the fused-silica capillary, on-column frits have to be produced at the end of the packing bed.Several frit-making methods have been developed. Sintering a silica packing material 10 or together with sodium silicate 11 has often been used for end-frit making. However, a partially intense heating in the sintering process can destroy the structure of particles, leading to some active sites on the surface of the fri...

Fritting techniques in chromatography

“…This technique is mostly used for packed silica capillary columns where the monolith frit is made chemically bonded to the inner surface of capillary. Organic or inorganic monolith polymer is formed either directly in the capillary column or into the first capillary (column) in the form of second capillary filled with monolithic material . In the case of inorganic monolith, the sol–gel technique is used, and this approach will be introduced in another section.…”

“…The monolith frits were made either by thermal or photoactuated polymerization. The frit could be placed at any desired position along the column especially in photopolymerization by removing the polyimide coating at the desired position when illuminating UV and/or blocking the remaining part by aluminum foil.…”

“…LED photopolymerization was also employed . Applications in both LC and CEC were reported. Semipreparative CEC with a packed column of 0.53 mm id was also carried out .…”

High-performance liquid chromatography on glass chips using precisely defined porous polymer monoliths as particle retaining elements

“…PPMs have been employed as particle retaining elements in nano-LC capillary columns [26]. Such porous sections are fabricated by either thermal polymerisation [27,28] or local photopolymerisation of a pre-polymeric mixture [29]. The generated frits cannot be longer than a few millimetres since the columns typically utilised have lengths of several centimetres.…”

Comparison of different types of outlet frits in slurry‐packed capillary columns

“…Even when the monolith properties are known, such as in the case of methacrylate monoliths studied by Peters et al , the effect of monolithic frit on packed column performance is uncertain. Ma et al used a frit based on butyl methacrylate while D'Orazio and Fanali chose glycidyl methacrylate hydrolyzed with sulfuric acid , both for reversed chromatography on a C 18 stationary phase. These monoliths, however, differ greatly in their hydrophilicity and thus they may influence the column performance differently.…”