Preparation of a capillary isoelectric focusing column with monolithic immobilized pH gradient and its application on protein separation based on an online capillary isoelectric focusing platform.

In the presence of methanol and n-decanol as porogens, a partially filled capillary monolithic column was prepared by in situ reaction of glycidyl methacrylate and poly (ethylene glycol) diacrylate. Then, Pharmalyte 3-10 was immobilized on this column in order to obtain a capillary isoelectric focusing (cIEF) column with monolithic immobilized pH gradient (M-IPG). In addition, an online self-built platform for protein separation was established on account of the introduction of a cross-shaped unit and two short-off valves. In this platform, a cross-shaped unit was not only used to join the M-IPG column and a six-way injection valve (1.5 μL sample loop), but also to supply a volume pool of anode buffer so that the process of injection, focusing and mobilization of samples could be sequentially performed. The short-off valve in the tee unit or cross-shaped unit could be used to control the direction of the fluid flow. Using this online cIEF platform and under the optimized conditions, 7-proteins mixture could be separated and a good linear correlation between pI values and migration times was obtained by the M-IPG column. Meanwhile, based on the online cIEF platform, human serum proteins and a mixture of Hb A and Hb A1c have been successfully resolved with the newly developed M-IPG column.