Performance of a sheathless porous tip sprayer for capillary electrophoresis-electrospray ionization-mass spectrometry of intact proteins

The performance of a prototype porous tip sprayer for sheathless capillary electrophoresis-mass spectrometry (CE-MS) of intact proteins was studied Capillaries with a porous tip were inserted in a stainless steel needle filled with static conductive liquid and installed in a conventional electrospray ionization (ESI) source Using a BCE of 100 mM acetic acid (pH 3 1) and a positively charged capillary coating a highly reproducible and efficient separation of four model proteins (insulin carbonic anhydrase II ribonuclease A and lysozyme) was obtained The protein mass spectra were of good quality allowing reliable mass determination of the proteins and some of their impurities Sheath-liquid CE-MS using the same porous tip capillary and an isopropanol-water-acetic acid sheath liquid showed slightly lower to similar analyte responses However as noise levels increased with sheath-liquid CE-MS detection limits were improved by a factor 6 5-20 with sheathless CE-MS The analyte response in sheathless CE-MS could be enhanced using a nanoESI source and adding 5% isopropanol to the BCE leading to improved detection limits by 50-fold to 140-fold as compared to sheath liquid interfacing using the same capillary - equivalent to sub-nM detection limits for three out of four proteins Clearly the sheathless porous tip sprayer provides high sensitivity CE-MS of intact proteins (C) 2010 Elsevier B V All rights reserved