High Capacity Capillary Electrophoresis-Electrospray Ionization Mass Spectrometry: Coupling a Porous Sheathless Interface with Transient-Isotachophoresis

Abstract

A sheathless interface making use of a porous tip has been used for coupling capillary electrophoresis and electrospray ionization mass spectrometry. First, effective flow rates using the interface have been characterized. It was found that the interface is capable of generating a stable spray with flow rates ranging from below 10 nL/min to >340 nL/min, enabling its use in either the mass or concentration-sensitive region of the electrospray process. Subsequently, by analyzing peptide mixtures of increasing complexity, we have demonstrated that this platform provides exquisite sensitivity enabling the detection of very low amounts of materials with very high resolving power. Transient isotachophoresis (t-ITP) can also be integrated with this setup to increase the mass loading of the system while maintaining peak efficiency and resolution. Concentration limits of detection in the subnanomolar or nanomolar range can be achieved with or without t-ITP, respectively. The application of a vacuum at the inlet of the separation capillary further allowed the peak capacity of the system to be improved while also enhancing its efficiency. As a final step in this study, it was demonstrated that the intrinsic properties of the interface allows the use of coated noncharged surfaces so that very high peak capacities can be achieved.

Comparing and Combining Capillary Electrophoresis Electrospray Ionization Mass Spectrometry and Nano–Liquid Chromatography Electrospray Ionization Mass Spectrometry for the Characterization of Post-translationally Modified Histones

“…Generally, sensitivity increases with decreasing flow rates. For example, Busnel et al obtained a 20-fold increase in sensitivity by decreasing the flow rate from 330 nl/min to 10 nl/min (40). Another advantage of minimal flow rates below 20 nl/min is the operation in the mass sensitive range of the ESI process, resulting in significantly reduced analyte suppression and improved sensitivity (55,56).…”

“…5A). In order to increase the mass loading of the system, transient isotachophoresis was integrated as an in-capillary pre-concentration procedure (40). However, applying 10 times more sample (3 pmol) did not result in any further increase in the number of peptide identifications (data not shown).…”

“…Busnel et al recently demonstrated that neutral capillaries are well suited for the separation of peptide mixtures using CESI-MS (40). The analysis of the 300-fmol histone H1 digest was performed using 10% acetic acid as the BGE, a separation voltage of 30 kV, and a pressure of 0.5 psi applied at the capillary inlet, which is needed to provide a stable spray over the entire duration of the experiment.…”

“…Applications such as the analysis of intact proteins (42), protein-protein and protein-metal complexes (43), and ribosomal protein digests from E. coli (44) have been published. Method-inherent advantages of CESI-MS are highly efficient separations, low flow rates leading to reduced ion suppression, and greater sensitivity (40). In contrast to nano-LC, no column equilibration is needed, there are no gradient effects, and the instrumentation is less maintenance-intensive.…”

High‐sensitive protein analysis by FESI‐CE‐MALDI‐MS

“…In the last two decades, it has also been demonstrated in various studies that its combination with MS provides a very powerful analytical platform for the characterization of peptides and/or protein mixtures [1,2].…”