A colloidal graphite-coated emitter for sheathless capillary electrophoresis/nanoelectrospray ionization mass spectrometry

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A colloidal graphite-coated emitter is introduced for sheathless capillary electrophoresis/nanoelectrospray ionization time-of-flight mass spectrometry (CE/ESI-TOFMS). The conductive coating can be produced by brushing the capillary tip to construct a fine layer of 2-propanol-based colloidal graphite. The fabrication involves a single step and requires less than 2 min. Full cure properties develop in ∼2 h at room temperature and then the tip is ready for use. The coated capillary tip is applied as a sheathless electrospray emitter. The emitter has proven to bear stable electrospray and excellent performance for 50 μm i.d. × 360 μm o.d. and 20 μm i.d. × 360 μm o.d. capillaries within the flow rate of 80-500 nL/min; continuous electrospray can last for over 200 h in positive mode. Baseline separation and structure elucidation of two clinically interesting basic drugs, risperidone and 9-hydroxyrisperidone, are achieved by coupling pressure-assisted CE to ESI-TOFMS using the described sheathless electrospray emitter with a bare fused-silica capillary at pH 6.7. It is found that the signal intensity of m/z in sheathless CE/ESI-TOFMS at pH 6.7 is ∼50 times higher than that at pH 9.0 for the two analytes, although the electroosmotic flow (EOF) at pH 9.0 provides sufficient flow rate (∼150 nL/min) to maintain electrospray.

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Analytical Chemistry

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