Electrospray ionization analyses are carried out on a FinniganMAT
LCQ (Thermoquest Corp, San Jose, CA) mass spectrometer system.
The electrospray needle voltage is typically set at 3.5kV, the
heated capillary voltage to 10V and the capillary temperature 225C.
Typical background source pressure is 1.2 x 10-5 torr as
read by an ion gauge. The
sample flow rate is approximately 10 microliters per minute.
The drying gas is nitrogen. The
LCQ is scanned to 2000 amu for most experiments.
The sample can be dissolved in acetonitrile, water, methanol,
acetic acid or formic acid.
The MS/MS results are obtained by selecting the ion of
interest (the precursor ion). The
precursor ion is then subjected to collision-induced dissociation (CID)
resulting in the formation of product ions.
Helium is introduced into the system to an estimated pressure of 1
millitorr to improve trapping efficiency and also acts as the collision
gas during the collisionally-induced dissociation (CID) experiments.
The collision energy is typically set to 32.5% of the maximum
available from the 5 volt tickle voltage.
(The relative collision energy varies from 0-100% for
collision-induced dissociation (0-5 volt peak to peak of the resonance
excitation rf voltage)
