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-mum-i.d., 90-mum-o.d. beveled tapered c apillary tip was similar to a conventional flat tapered tip with a 25-mum o rifice. Using a mixture of coptisine, berberine, and palmatine chloride, th e sheathless CE/ESI-MS sensitivity of a beveled 75 mum tapered tip capillar y was found to be similar to a 25 mum flat tip. Although both tips offer si milar CE/ESI-MS sensitivity, the beveled tapered capillary tip is more rugg ed and durable than a conventional 25-mum tapered capillary because of the larger outside diameter and inside diameter. To make electrical contact, th e capillary tip was smeared with paint marker followed by the application o f a carbon coating using a graphite pencil. Using this refined carbon-coati ng procedure, the capillary tip can be operated with aprotic solvents.