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 BGE 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 BGE, 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.
Haselberg
Rob
R
Department of Biomedical Analysis, Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands. r.haselberg@uu.nl
Ratnayake
Chitra K
CK
de Jong
Gerhardus J
GJ
Somsen
Govert W
GW
D019075:Electrophoresis, Capillary / Q000295:instrumentation / Q000379:methods*; D011506:Proteins; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
D011506:Proteins