data were acquired using an LTQ Velos Pro linear ion trap mass spectrometer
(Thermo Scientific) equipped with a heated ESI probe coupled in-line
to the RP-UHPLC system. Nitrogen was used both as sheath gas (47 arbitrary
units) and auxiliary gas (11 arbitrary units). Data were collected
in negative ionization mode over the m/z range 150–1500 for untargeted analysis and 300–1500
for targeted analysis of higher molecular weight compounds. Data-dependent
MSn analyses were performed by collision-induced
dissociation (CID) with a normalized collision energy of 35%. MSn fragmentation was performed on the most intense
product ion in the MSn–1 spectrum. Dynamic exclusion with a repeat count of 3, repeat duration
of 5 s, and an exclusion duration of 5 s was used to obtain MSn spectra of multiple different ions present
in full MS at the same time. Most settings were optimized by automatic
tuning using LTQ Tune Plus 4.2 in Xcalibur 4.2 (Thermo Scientific).
The ion-transfer tube temperature was 350 °C, the source heater
temperature was 408 °C, and the source voltage was 4.0 kV. Data
were processed using Xcalibur 4.2 (Thermo Scientific).