2.2 Mass Spectrometry
The high-resolution ESI-MS and subsequent high-resolution ESI-MS/MS
experiments were performed on a Q Exactive HF Orbitrap mass spectrometer
(Thermo Fisher Scientific Inc., Waltham, MA, USA) equipped with a
standard ESI interface. Nitrogen was used as the sheath gas, auxiliary
gas and collision gas. The basic ESI conditions were: spray voltage,
3500 V; capillary temperature, 275 °C; probe heater temperature, 300 °C;
sheath gas flow rate, 35 arbitrary units; auxiliary gas flow rate, 10
arbitrary units; while the selected collision energy depended on the
dissociation capability of the precursor ions. Data acquisition and
analysis were carried out with the Xcalibur software package (version
4.2.47, Thermo Scientific).