ON THE USE OF SCANS AT A CONSTANT RATIO OF B E FOR STUDYING DECOMPOSITIONS OF PEPTIDE METAL(II)-ION COMPLEXES FORMED BY ELECTROSPRAY-IONIZATION/

The use of sector mass spectrometers to study metastable ion decomposi tions of peptide metal-ion complexes formed by electrospray ionization is discussed. Products that are formed by charge-separation reactions are characterized by large kinetic energy release distributions. This causes scans at a constant B/E to give incorrect product ion abundanc es and possibly incorrect mass assignments. Two instrumental methods e xist that can be used either to detect the ions or to estimate relativ e ion abundances: a floated collision cell or mass-analyzed ion kineti c energy spectrometry (MIKES) scans. The floated collision cell, by vi rtue of an altered B/E scan law, however, discriminates against import ant metastable ion reactions that occur outside the cell. MIKES scans provide a clearer estimate of product ions that arise by metastable io n charge-separation reactions. Problems with pseudotandem (first field -free region) experiments are also discussed.