Collision-induced dissociation of 30 m/z unit wide windows of electrospray-generated ions sampled under lens conditions of nominally zero potential gradient.

Windows 30 m/z units wide of ions generated in electrospray and sampled under lens conditions of nominally zero potential gradient conditions were mass selected with Q1 in a triple-quadrupole mass spectrometer, fragmented in Q2, and their product ions mass analysed with Q3. A variety of analytes (equine myoglobin, bovine insulin, leucine enkephalin and PPG 1000) were examined. The windows selected sometimes contained desolvated (bare) analyte ions; more often they did not and contained only 'background' ions. For protein samples, multiply charged product ions having m/z values both lower and higher than those of the precursor ions were observed even when the precursor ion window could not have contained naked protein dimer ions. To observe significant product ions, the precursor ion window typically contained ions residing within background 'humps' that trailed protein peaks. These ions were speculated to be diverse, solvated multimeric clusters of the analyte which fragmented in Q2 to yield the characteristic product ion spectra.