Use of an Ion Trap Storage/Reflectron Time-of-Flight Mass Spectrometer as a Rapid and Sensitive Detector for Capillary Electrophoresis in Protein Digest Analysis

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Abstract
An ion trap storage (IT)/reflectron time-of-flight mass spectrometer (reTOFMS) has been coupled to capillary electrophoresis (CE) via a sheathless microelectrospray ionization method. This hybrid mass spectrometer has proved to be a rapid and sensitive detector for CE, where mass spectra could be acquired at a speed sufficient to maintain the high-resolution capabilities of CE separations. The nonscanning property of the time-of-flight mass analyzer can provide a full mass range spectral acquisition speed of up to 25 spectra/s with a data system developed in our laboratory. For the work reported herein, a spectral acquisition speed of 4 spectra/s was found to be optimal for maintaining the quality of the separation while achieving high sensitivity. Tryptic digests of bovine cytochrome c and β-lactoglobulin A were analyzed using the CE/IT/reTOFMS combination, resulting in total ion electropherograms similar to those obtained using UV absorption detection. Taking advantage of the ion storage capability of the ion trap, a detection limit in the low-femtomole range was routinely obtained for these digests using the total ion electrophoretic mode and CE capillaries of typical dimensions (41 μm i.d.). This high sensitivity was achieved while maintaining a resolution of ∼1500 for mass identification using the capabilities of the IT/reTOF device. Due to the high acquisition speed and the mass discrimination capabilities of the mass detector, all the peaks in the total ion electropherograms, including some totally or partially unresolved peaks, could be unambiguously identified.