A new scan mode for the identification of multiply charged ions

A new scan mode is demonstrated for the identification of the presence of multiply charged ions in a mixture which contains singly charged background ions. This scan mode can be used to identify candidates for MS/MS in a complex mixture of ions, where multiply charged peptide ions are preferred for obtaining sequence information. In contrast with the conventional precursor ion scan mode, the new scan mode is more sensitive and provides a more general screening tool in the selection of candidate peptide and protein ions for MS/MS. It can be applied with triple-quadrupole and quadrupole/time-of-flight tandem mass spectrometers.