Reagent for mass spectrometry

A reagent, which is a compound of formula (Ia)

• X-L1-Y-L2-Z
• wherein
• X is a carbonyl reactive group, dienophilic group, a carboxylate reactive group, a phenol reactive group, an amino reactive group, a hydroxyl reactive group, or a thiol reactive group, and wherein X is no acrylester,
• L1 is a bond or a spacer,
• Y is a neutral ion loss unit which, under conditions of mass spectrometry, is capable of fragmentation, whereby a neutral species, particularly a low-molecular weight neutral species, is released,
• L2 is a bond or a spacer,
• Z is a charge unit comprising at least one permanently positively charged moiety,
• including any salt thereof, or a composition or kit comprising at least one compound (Ia).

A reagent, which is a compound of formula (Ia)

• X-L1-Y-L2-Z
• wherein
• X is a carbonyl reactive group, dienophilic group, a carboxylate reactive group, a phenol reactive group, an amino reactive group, or a hydroxyl reactive group,
• L1 is a bond or a spacer,
• Y is a neutral ion loss unit which, under conditions of mass spectrometry, is capable of fragmentation, whereby a neutral species, particularly a low-molecular weight neutral species, is released,
• L2 is a bond or a spacer,
• Z is a charge unit comprising at least one permanently negatively charged moiety,
• including any salt thereof, or a composition or kit comprising at least one compound (Ia).

A covalent adduct formed by reaction of the compound of general formula (I)

• X-L1-Y(-L2-Z)r
• wherein
• X is a reactive group capable of reacting with an analyte molecule, whereby a covalent bond with the analyte molecule is formed,
• L1 is a bond or a spacer,
• Y is a neutral ion loss unit which, under conditions of mass spectrometry, is capable of fragmentation, whereby a neutral species, particularly a low-molecular weight neutral species is released,
• L2 is a bond or a spacer,
• Z is a charge unit comprising at least one charged moiety, in particular a permanently charged moiety,
• r is 0 or 1,
• including any salt thereof,
• and an analyte molecule.