Thermo exactive orbitrap mass spectrometer

Mass spectra were acquired on a Thermo
Orbitrap Exactive mass spectrometer (Thermo Scientific, San Jose,
CA). In the conventional atmospheric ESI source configuration a standard
heated capillary interface was used as illustrated in Figure 1a. The temperature of the heated capillary inlet
was adjusted from 150 to 300 °C, and the dc voltages on the tube
lens and skimmer were adjusted to achieve either optimal sensitivity
or ionization gentleness. The instrument was tuned using the LTQ Velos ESI positive ion calibration
solution (Thermo Scientific, San Jose, CA). In the SPIN source configuration
the ESI emitter was moved to the first vacuum region of the mass spectrometer
and positioned at the entrance of the ion funnel.^{15 (link),18 (link)} As depicted in Figure 1b, in this configuration
the standard ion optics up to lens L0 were replaced by two ion funnels
operating at different vacuum pressures. Independent of the source
configuration the instrument was always operated in ultrahigh-resolution
mode with an m/z range of 200–3000
with a 3 microscan average per spectrum. The AGC was set for high
dynamic range with a maximum ion injection time of 100 ms. Electrospray
emitters were fabricated by chemically etching fused-silica capillary
tubing with a 10 μm i.d. and 150 μm o.d. (Polymicro Technologies,
Phoenix, AZ) as described previously.^{24 (link)}