A simple sheathless CE-MS interface with a sub-micrometer electrical contact fracture for sensitive analysis of peptide and protein samples

• Published in: Analytica chimica acta Vol. 936; pp. 157 - 167
• Main Authors: Nguyen, Tam T.T.N., Petersen, Nickolaj J., Rand, Kasper D.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 14-09-2016
• Subjects: Native MS; Peptide mapping; Protein ESI-MS; Protein/peptide analysis; Sheathless CE-MS interface; Sub-micrometer fracture; Protein ESI-MS; Sheathless CE-MS interface; Protein/peptide analysis; Peptide mapping; Sub-micrometer fracture; Native MS
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2016.07.002

Online coupling of capillary electrophoresis (CE) to electrospray ionization mass spectrometry (MS) has shown considerable potential, however, technical challenges have limited its use. In this study, we have developed a simple and sensitive sheathless CE-MS interface based on the novel concept of forming a sub-micrometer fracture directly in the capillary. The simple interface design allowed the generation of a stable ESI spray capable of ionization at low nanoliter flow-rates (45–90 nL/min) for high sensitivity MS analysis of challenging samples like those containing proteins and peptides. By analysis of a model peptide (leucine enkephalin), a limit of detection (LOD) of 0.045 pmol/μL (corresponding to 67 attomol in a sample volume of ∼15 nL) was obtained. The merit of the CE-MS approach was demonstrated by analysis of bovine serum albumin (BSA) tryptic peptides. A well-resolved separation profile was achieved and comparable sequence coverage was obtained by the CE-MS method (73%) compared to a representative UPLC-MS method (77%). The CE-MS interface was subsequently used to analyse a more complex sample of pharmaceutically relevant human proteins including insulin, tissue factor and α-synuclein. Efficient separation and protein ESI mass spectra of adequate quality could be achieved using only a small amount of sample (30 fmol). In addition, analysis of ubiquitin samples under both native and denatured conditions, indicate that the CE-MS setup can facilitate native MS applications to probe the conformational properties of proteins. Thus, the described CE-MS setup should be useful for a wide range of high-sensitivity applications in protein research.
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•We develop a sheathless CE-MS interface with a sub-micron fracture directly in the capillary for electrical contact.•The simple design facilitates a stable ESI spray, a low (attomol) detection limit and well-resolved CE separation.•We apply the CE-MS setup for analysis of complex samples including mixtures of peptides and proteins.•We demonstrate that the CE-MS method can also facilitate native MS applications.