Patent ID: 7556969

Claim:
A method for detecting an analyte, said method comprising the steps of: covalently labeling an analyte, to produce a tag-analyte molecule, with a molecular tag of the form: XxyYZ, wherein Z is a reactivity group that enables XxyYZ to be attached covalently to analyte (A) to form product XxyYZ-A; Xxy is a group that bears a charge; Y is a group comprising an unsaturated group; x and y are atoms that are connected to each other by a single bond; y is connected to an unsaturated group of Y by a single bond; XxyYZ-A becomes an ion (XxyYZ-A ion) in the gas phase of the first stage of tandem mass spectrometry analysis; and said XxyYZ-A ion undergoes cleavage upon energetic activation in the second stage of tandem mass spectrometry analysis to form a neutral species Xx and a resonance stabilized daughter ion yYZ-A wherein the charge on daughter ion yYZ-A is resonantly stabilized by distribution between y and said unsaturated group of Y; causing said tag-analyte molecule to become a parent tag-analyte ion (XxyYZ-A ion) in the first stage of a tandem mass spectrometer; and causing said parent tag-analyte ion to fragment through cleavage from energetic activation to become a resonance stabilized daughter tag-analyte ion (yYZ-A ion) in the second stage of a tandem mass spectrometer, wherein said daughter tag-analyte ion forms from loss of a neutral fragment (Xx) from said parent tag-analyte ion, wherein said neutral fragment comes from the tag portion of said parent tag-analyte ion and wherein said resonance stabilized daughter ion yYZ-A is predominant relative to any other ion detected from said tag-analyte.