Nanoelectrospray mass spectrometry using non-metalized, tapered (50 → 10 μm) fused-silica capillaries

Abstract

Nanoelectrospray emitter tips, pulled from fused-silica capillaries requiring no chemical treatment or metal coating, have been operated using remote coupling of the electrospray voltage. Using common laboratory implements, 50 μm i.d. fused-silica capillaries were pulled to ca. 10 μm, and attached to a stainless steel capillary via a teflon coupler for the production of nanoelectrospray (i.e. nL/min flowrates). Using a variety of different tips, flowrates were determined to range from 30 to 80 nL/min. Spectra of bovine insulin (ca. 6 kDa) and Angiotensin III (ca. 1 kDa) produced signal-to-noise (S/N) ratios of ca.500 and ca.100, respectively; each analysis consuming ca. 10 femtomoles of sample. Radical cation formation, in addition to the monoprotonated molecule was also observed during nanoelectrospray of angiotensin III which implies that this nanoelectrospray source should be applicable to trace amounts of non-polar compounds. The stability of the ion source is demonstrated by measuring the current of the electrosprayed ions at the shutter of the Fourier transform ion cyclotron resonance mass spectrometer as a function of time. Overall stability of the nanoelectrospray for angiotensin III, using no pressure to initialize or stabilize the electrospray, was determined as 23 pA ± 0.97 pA (4.2 % relative standard deviation) over a 30 minute period. © 1998 John Wiley & Sons, Ltd.