The mass spectrometer utilized the following parameters: an Agilent multimode source which simultaneously acquires ESI+/APCI+; a reference mass solution consisting of purine and hexakis(1 H-tetrafluoropropoxyophosphazineosphandne; and a makeup solvent of 90:10:0.1 MeOH/H2O/HCO2H, which was introduced to the LC flow prior to the source to assist ionization.
Two different kinds of mass spectrometers were utilized in this study: nanospray (NSI /LTQ FT (Thermo Finnigan) and matrix assisted laser desorption ionization (MALDI /TOF/TOF (Applied Biosystems).
A TSQ Vantage triple-quadrupole mass spectrometer (Thermo Fisher Scientific, San Jose, CA) was utilized for the scheduled LC-MRM analysis with on-the-fly correction for retention time (RT) shift.
A Quattro Premier XE tandem mass spectrometer from Waters-Micromass was utilized for analyte detection.
In addition, HPLC-MS/MS analysis was conducted on an Esquire plus 3000 (Bruker Daltonics, Billerica, MA, USA) ion trap mass spectrometer with an electrospray interface (ESI) utilizing HPLC eluted with the mobile phase consisted of 25 mM NH4OAc as well as 25 mM NH4OH in water, and acetonitrile (90 10).
Mass spectrometric analyses of tryptic peptides were carried out on a MALDI VOYAGER DE-PRO time of flight mass spectrometer from PerSeptive BioSystems (Framingham, MA) utilizing a nitrogen laser, emitting at 337 nm, and an accelerating voltage of 25 kV.
Because isotopes differ in mass, their relative abundance can be determined if the masses are separated in a mass spectrometer (see below Use of mass spectrometers).
MS detection utilized micrOTOF-QII mass spectrometer (Bruker, Bremen, Germany).
Moreover, by utilizing a two-sector-field mass spectrometer we investigated metastable and collision-induced decays of [ M−H]− at different resonance energies to shed some light on the isomeric structure of the [ M−H]− formed.
To solve this question we utilized the two-sector-field mass spectrometer and studied the fragmentation pattern of the anion [ M−H]− formed at low electron energies.
