Weak cation-exchange monolithic column for capillary liquid chromatography of peptides and proteins

A simple microfluidic chip design for fundamental bioseparation

A microchip pressure-driven liquid chromatographic system with a packed column has been designed and fabricated by using poly(dimethylsiloxane) (PDMS). The liquid chromatographic column was packed with mesoporous silica beads of Ia3d space group. Separation of dyes and biopolymers was carried out to verify the performance of the chip. A mixture of dyes (fluorescein and rhodamine B) and a biopolymer mixture (10 kDa Dextran and 66 kDa BSA) were separated and the fluorescence technique was employed to detect the movement of the molecules. Fluorescein molecule was a nonretained species and rhodamine B was attached onto silica surface when dye mixture in deionized water was injected into the microchannel. The retention times for dextran molecule and BSA molecule in biopolymer separation experiment were 45 s and 120 s, respectively. Retention factor was estimated to be 3.3 for dextran and 10.4 for BSA. The selectivity was 3.2 and resolution was 10.7. Good separation of dyes and biopolymers was achieved and the chip design was verified.

Epoxy-based monoliths for capillary liquid chromatography of small and large molecules

A versatile epoxy-based monolith was synthesised by polycondensation polymerisation of glycidyl ether 100 with ethylenediamine using a porogenic system consisting of polyethylene glycol, M(w) = 1000, and 1-decanol. Polymerisation was performed at 80 °C for 22 h. A simple acid hydrolysis of residual epoxides resulted in a mixed diol-amino chemistry. The modified column was used successfully for hydrophilic interaction liquid chromatography (HILIC) of small molecule probes such as nucleic acid bases and nucleosides, benzoic acid derivatives, as well as for peptides released from a tryptic digest of cytochrome c. The mixed-mode chemistry allowed both hydrophilic partitioning and ion-exchange (IEX) interactions to contribute to the separation, providing flexibility in selectivity control. Residual epoxide groups were also exploited for incorporating a mixed IEX chemistry. Alternatively, the surface chemistry of the monolith pore surface rendered hydrophobic via grafting of a co-polymerised hydrophobic hydrogel. The inherent hydrophilicity of the monolith scaffold also enabled high performance separation of proteins under IEX and hydrophobic interaction modes and in the absence of non-specific interactions.