Fixation of nitrogen in an electrospray mass spectrometer.

The formation of an iron-nitrogen compound in an electrospray ionization instrument is reported. The iron was released from the stainless steel electrospray needle by acetic acid added to displace trifluoroacetic acid and the nitrogen was present as the drying gas. The product is an iron nitride ion, [N(2)FeOH](1+), m/z 100.9438, and is capable of addition to peptides and proteins.