title: A modified internal lock-mass method for calibration of the product ions derived from sustained off-resonance irradiation collision-induced dissociation using a Fourier transform mass spectrometer.
abstract: A modified internal lock-mass calibration method is introduced for improving the mass measurement accuracy of the product ion spectra derived from sustained off-resonance irradiation collision-induced dissociation (SORI-CID) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. This method involves an initial external calibration of the Fourier transform mass spectrometer to obtain the initial A- and B-terms for the equation (f(i) = A/(m/z)(i) + B). The A-term is adjusted by using an empirical relationship between the up-shift of the A-term and the pulse-gas duration, whereas the B-term is adjusted by using the mass of the unfragmented precursor ion from the SORI-CID mass spectrum of the unknown sample as internal lock-mass. These adjusted A- and B-terms are then used to provide exact mass SORI-CID calibration for the unknown sample. The modified internal lock-mass method achieved average mass measurement accuracy of approximately 3 ppm which is significantly better than that of the conventional internal lock-mass calibration ( approximately 9 ppm) and is approaching that of the internal calibration ( approximately 2 ppm) and requires no addition of internal calibrant or instrumental modifications.
authors.affiliation: Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong.
authors.forename: Lifang
authors.initials: L
authors.lastname: Duan
authors.forename: T-W Dominic
authors.initials: TW
authors.lastname: Chan
mesh_terms: D000804:Angiotensin II / Q000032:analysis; D000818:Animals; D001920:Bradykinin / Q000032:analysis; D002138:Calibration; D007477:Ions / Q000032:analysis*; D008555:Melitten / Q000032:analysis; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D007477:Ions; D000804:Angiotensin II; D008555:Melitten; D001920:Bradykinin