Design and performance of an electrospray ionization time-of-flight mass spectrometer

In order to circumvent the limitations of a quadrupole mass filter, which so far has been the most common mass analyzer for use with electrospray ionization, a mass spectrometer coupling electrospray with time-of-flight mass analysis has been constructed. The design of this spectrometer, including a simple electrospray ion source, an atmosphere–vacuum interface without a rf-only quadrupole/multipole that discriminates against low mass ions which can be used for internal calibration, orthogonal extraction, and a reflectron, is presented together with its performance characteristics. A resolving power of 7500 was obtained for the +5 ion of bovine insulin and the detection limit for the same molecule was shown to be 1 f mol. Mass accuracy using a conventional two-point calibration is 60 ppm for internal calibration on low mass ions and better than 100 ppm for external calibration on peptide ions. An improved mass accuracy equal to 10 ppm was achieved using internal three-point calibration on low mass ions naturally present in the spectra. The dynamic range of a single sample was found to be at least 400:1.