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

In order to circumvent the limitations of a quadrupole mass filter, which s o far has been the most common mass analyzer for use with electrospray ioni zation, 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 r f-only quadrupole/multipole that discriminates against low mass ions which can be used for internal calibration, orthogonal extraction, and a reflectr on, is presented together with its performance characteristics. A resolving power of 7500 was obtained for the +5 ion of bovine insulin and the detect ion limit for the same molecule was shown to be 1 f mol. Mass accuracy usin g a conventional two-point calibration is 60 ppm for internal calibration o n 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 interna l 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. (C) 2000 American Institute of Physics. [S0034-6748(00)02101-8].