The LTQ Orbitrap MS was equipped
with an ESI source operating in both positive and negative ioniza-
tion mode using the following operating parameters: electrospray
voltage 3.1 kV, sheath gas flow rate 8 arbitrary unity (abu), auxili-
ary gas flow rate 1 abu, capillary temperature 543 K, capillary volt-
age 49.00 V, tube lens offset 148.43 V.