Assessment of capillary electrophoresis TOF MS for a confident identification of peptides

CE on-line coupled to orthogonal accelerated TOF-MS (CE-oa-TOF-MS) is an emerging technique offering efficient charge-to-mass-based separations, as well as accurate and high-resolution mass measurements. Here, we investigated the main factors influencing the analysis of low molecular mass peptides using a sheath-flow electrospray ionization interface and several neuropeptides as model compounds. Moderate fragmentor voltage values of the oa-TOF-MS were crucial to maximize the production of molecular ions for optimum sensitivity precluding molecular fragmentation. However, the major fragments provided specific information that may result valuable for confirmatory purposes. Advantages and disadvantages of adding internal mass references to the sheath liquid for continuous mass-to-charge recalibration during the electrophoretic separations were discussed with regard to mass accuracy and sensitivity. Furthermore, several instrumental modes related to mass resolution were also examined. Finally, the method was validated for quantitative analysis of the studied neuropeptides in terms of repeatability, linearity and LODs. The results obtained using CE-oa-TOF-MS were compared with those obtained using CE coupled to other mass spectrometers. In addition to the simplicity and reliability on the identification, CE-oa-TOF-MS allowed improved repeatability and an around 10-fold improvement in sensitivity with respect to conventional reflectron TOF and ion trap mass analyzers.