Integrated strong cation-exchange hybrid monolith coupled with capillary zone electrophoresis and simultaneous dynamic pH junction for large-volume proteomic analysis by mass spectrometry

A sulfonate-silica hybrid strong cation-exchange (SCX) monolith was synthesized at the proximal end of a capillary zone electrophoresis column and used for on-line solid-phase extraction (SPE) sample preconcentration. Sample was prepared in an acidic buffer and deposited onto the SCX-SPE monolith and eluted using a basic buffer. Electrophoresis was performed in an acidic buffer. This combination of buffers results in formation of a dynamic pH junction, which allows use of relatively large elution buffer volume while maintaining peak efficiency and resolution. All experiments were performed with a 50 pm ID capillary, a 1 cm long SCX-SPE monolith, a 60 cm long separation capillary, and a electrokinetically pumped nanospray interface. The volume of the capillary is 1.1 mu L. By loading 21 mu L of a 1 x 10(-7) M angiotensin II solution, an enrichment factor of 3000 compared to standard electrokinetic injection was achieved on this platform while retaining efficient electrophoretic performance (N=44,000 plates). The loading capacity of the stlfonate SCX hybrid monolith was determined to be similar to 15 pmol by frontal analysis with 10(-5) M angiotensin II. The system was also applied to the analysis of a 10(-4) mg/mL bovine serum albumin tryptic digest; the protein coverage was 12% and 11 peptides were identified. Finally, by loading 5.5 mu L of a 10(-3) mg/mL E. coli digest, 109 proteins and 271 peptides were identified in a 20 min separation; the median separation efficiency generated by these peptides was 25,000 theoretical plates. (C) 2015 Elsevier B.V. All rights reserved.