Fig. 1. A tandem mass spectrum of synthetic let-7 denoting all of the assigned peaks.

a-B/a/b/c/d ions are shown in red, w/x/y/z ions in green. The primary ion was deprotonated seven times to give a charge state of −7 (m/z 971.55). The ion coverage plot in the upper right shows coverage for nine different types of fragment ion.