Iron carboxylate oxygen-centered-triangle complexes detected during electrospray use of organic acid modifiers with a comment on the finnigan TSQ-700 electrospray inlet system.

Use of infusion methods rather than high-performance liquid chromatography allowed us to confirm the observation that solutions of propionic acid-isopropanol restore sensitivity lost due to trifluoroacetic acid in electrospray mass spectra of basic substances, particularly peptides. In this work, when propionic acid-isopropanol was used, we detected an abundant ion with m/z 622 that shifted to m/z 538 when we substituted acetic acid-methanol for the propionic acid-isopropanol. Via accurate mass measurement and tandem mass spectrometry the origin of the ion was identified as the complex Fe3O(O2CR)6(L)0-3, where L is one of several ligands from solvent or water. The grounding arrangement of the Finnigan TSQ-700 electrospray source produces electrolytic currents that may accentuate the abundance of this complex and specifically produces observable gas bubbles that adversely affect the spray stability.