Sheathless capillary electrophoresis/electrospray mass spectrometry using a carbon-coated tapered fused-silica capillary with a beveled edge

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-μm-i.d., 90-μm-o.d. beveled tapered capillary tip was similar to a conventional flat tapered tip with a 25-μm orifice. Using a mixture of coptisine, berberine, and palmatine chloride, the sheathless CE/ESI-MS sensitivity of a beveled 75 μm tapered tip capillary was found to be similar to a 25 μm 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-μm 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.