Sheathless Capillary Electrophoresis/Electrospray Mass Spectrometry Using a Carbon-Coated Tapered Fused-Silica Capillary with a Beveled Edge

Abstract

A tapered capillary tip containing a beveled edge was developed for use in sheathless capillary electrophoresis/electrospray mass spectrometry (CE/ESI-MS). The optimal flow rate of a 75-microm-i.d., 90-microm-o.d. beveled tapered capillary tip was similar to a conventional flat tapered tip with a 25-microm orifice. Using a mixture of coptisine, berberine, and palmatine chloride, the sheathless CE/ ESI-MS sensitivity of a beveled 75 microm tapered tip capillary was found to be similar to a 25 microm flat tip. Although both tips offer similar CE/ESI-MS sensitivity, the beveled tapered capillary tip is more rugged and durable than a conventional 25-microm tapered capillary because of the larger outside diameter and inside diameter. To make electrical contact, the capillary tip was smeared with paint marker followed by the application of a carbon coating using a graphite pencil. Using this refined carbon-coating procedure, the capillary tip can be operated with aprotic solvents.

Comparison of sheathless and sheath‐flow electrospray interfaces for the capillary electrophoresis‐electrospray ionization‐mass spectrometry analysis of peptides

“…One side is polished manu-ally by applying the capillary to the rotating disk of emery paper at an angle of 307 and rolling it accurately to obtain a symmetrical shape. The sharpened tip is controlled under an optical microscope because its shape plays an important role in ESI [17]. Once the capillary was tapered, the polyimide coating of the last 2 cm was burned and removed from the silica capillary.…”

“…In this last case, different kinds of coating processes have been described: a chromium-gold layer deposited by an electron beam [11]; an electrodeless nickel-plating procedure [12]; mixtures of different polymers as polyimide, polypropilene, or silicone with gold and graphite particles [13][14][15][16]; and even by simple coating with a graphite pencil [17,18]. Recently, some commercial stainless or graphite-coated tips used in micro-and nanoelectrospray have been adapted as sheathless CE-ESI-MS tips [19].…”

Coupling CE with atmospheric pressure photoionization MS for pharmaceutical basic compounds: Optimization of operating parameters

“…Sheath liquid provides (i) electrical contact with the outlet end of the separation capillary, (ii) appropriate flow rate adapted to source configuration, and (iii) suitable solvent conditions for ionization and evaporation, independent on the nature of the BGE. Several sheathless interfaces [11][12][13][14][15][16][17] have also been investigated but still suffer from some important drawbacks (increased band broadening, higher background noise due to the lower total flow rate, lack of robustness).…”

Sheathless capillary electrophoresis‐mass spectrometry using a pulsed electrospray ionization source

“…One major drawback of using a sheath liquid interface is the reduction in sensitivity due to dilution of the sample as it elutes from the capillary. It is a well-known phenomenon that the optimal flow rate in ESI depends on the orifice of the emitter [11,21]. The intensities of signals increase with the flow rate.…”

“…In sheathless interface, several approaches including a pulled bare fused-silica capillary emitter, the conductive coating, connecting to a stainless-steel tip, and the use of a liquid junction [14,[10][11][12][22][23][24][25][26][27][28][29] have been proposed to maintain electrical continuity of the electrophoresis circuit. An important consequence of sheathless design is that the sample bands are not diluted.…”