A sheathless CE/ESI‐MS interface with an ionophore membrane‐packed electro‐conduction channel

Abstract

A robust and convenient sheathless CE/ESI-MS interface realized with an ionophore membrane-packed electro-conduction channel is described. Sheathless interfaces that may provide higher sensitivity for MS detection than sheath flow-supported interfaces generally show instability and short lifetimes due to their imperfection in making an electrical contact with the emitter tip. In this work, we designed a sheathless interface based on an ionophore membrane-packed electro-conduction channel. At the joining point of the CE capillary and the emitter capillary, the conduction channel was implemented toward the exterior of the interface body, where a platinum wire electrode was placed. The conduction channel transferred the electric field from the external Pt electrode to the joining point, but prevented the effluent of CE from leaking. The interface body was designed to have receptacles for standard capillary tubing with finger-tight fittings, which allowed easy replacement of capillary tubing. Stable electrospray was observed for an extended time period without any signs of bubbling or damage to the emitter tip. No significant increment of dead-volume at the interface was observed for well-aligned capillaries. Sensitive and stable CE-MS detection of the model compound of creatinine and uric acid was demonstrated.

Capillary electrophoresis mass spectrometry with sheathless electrospray ionization for high sensitivity analysis of underivatized amino acids

“…In our previous study, we reported that a gap between the two capillaries in the capillary channel could lead to significant peak tailing . In this work, we tightly butted two capillaries to minimize the dead volume and peak tailing introduced by the gap.…”

“…The sheathless CE/ESI‐MS interface was constructed based on the work of Shi et al . The expansion or trimming of fine holes on the interface was manually performed at our laboratory as necessary.…”

“…CE‐MS interfaces can be grouped into sheath‐flow and sheathless interfaces . Although commercially available CE‐MS instruments almost have adopted sheath‐flow interfaces, dilution of analytes by the dominating volume of the sheath liquid is unavoidable, and this could potentially lead to loss of sensitivity . Consequently, sheathless interfaces have been developed to avoid the dilution effect of the sheath liquid.…”

“…Easy fabrication and quick replacement would also be advantageous in routine applications. In a previous paper, we reported on the development of a two‐capillary sheathless CE/ESI‐MS interface with an ionophore membrane‐packed electro‐conduction channel, and demonstrated analysis of creatinine and uric acid with stable operation and good sensitivity . Fabrication and replacement of capillary tubing were readily achieved.…”

Recent advances in coupling capillary electrophoresis‐based separation techniques to ESI and MALDI‐MS

“…The challenges of building robust two‐piece sheathless interfaces lie in aligning the separation column end and emitter with minimum gap, and maintaining stable electric contact at the joint of the two pieces. In the design made by Park et al , two ports of a three‐port plastic tee were used to secure the separation column and the emitter, and the third one was packed with Nafion, which formed a conductive polymer layer that allows cations to move through. A piece of sponge soaked with electrolyte was placed on top of the Nafion layer and voltage for electrospray was applied through a platinum wire wrapping around the tee.…”