Mass labels

A set of mass labels, each mass label in the set comprising a mass marker moiety attached via a cleavable linker to a mass normalisation moiety, wherein when the linker is cleaved by dissociation in a mass spectrometer, each mass label is adapted to dissociate to form the mass marker moiety and the mass normalization moiety, each mass label in the set having a common mass;

• wherein
• the set comprises a plurality of groups of mass labels, the mass of the mass marker moiety being the same for mass labels within a group, the mass of the mass marker moiety being different between groups;
• the mass marker moiety is capable of fragmentation by collision induced dissociation in the mass spectrometer into two or more fragments;
• and
• the mass of at least one fragment of the mass marker moiety differs between mass labels within a group such that each mass marker moiety of the mass labels within a group is distinguishable from one another by mass spectrometry, wherein one or more mass labels in the set comprises one or more isotopic labels and wherein the isotopic label comprises 2H, 13C, 15N or 18O and, wherein each mass label in a group comprises a mass marker moiety which is the same chemical species, each mass label in the group comprising an isotopic marker at a different position in the mass marker moiety.

A set of mass labels, each mass label in the set comprising a mass marker moiety attached via a cleavable linker to a mass normalisation moiety, wherein when the linker is cleaved by dissociation in a mass spectrometer, each mass label is adapted to dissociate to form the mass marker moiety and the mass normalization moiety, each mass label in the set having a common mass;

• wherein
• the set comprises a plurality of groups of mass labels, the mass of the mass marker moiety being the same for mass labels within a group, the mass of the mass marker moiety being different between groups;
• the mass marker moiety is capable of fragmentation by collision induced dissociation in the mass spectrometer into two or more fragments;
• and
• the mass of at least one fragment of the mass marker moiety differs between mass labels within a group such that each mass marker moiety of the mass labels within a group is distinguishable from one another by mass spectrometry, wherein one or more mass labels in the set comprises one or more isotopic labels and wherein the isotopic label comprises 2H, 13C, 15N or 18O, the position of at least one isotopic label varying between mass labels in the group, such that at least one isotopic label is comprised in a different fragment of the mass marker moiety in each mass label in the group and, wherein each mass label in the set is the same chemical species, each mass label in the set comprises two or more isotopic labels, each mass label in the set comprises an equal number of isotopic labels, each mass label in a group comprises a first number of isotopic markers in the mass marker moiety and a second number of isotopic markers in the mass normalisation moiety, and the first number and the second number differs between groups.