Patent ID: 8853133

Claim:
A method comprising: a) reacting two or more samples, each sample comprising one or more reactive analytes, with a different labeling reagent of a set of isotopically encoded isobaric labeling reagents to thereby form two or more differentially labeled samples each comprising one or more labeled analytes wherein the different labeling reagents of the set are represented by formula; including a salt form thereof, wherein; i) RG is and wherein X′ is O or S and each X″ is independently of the other F, Cl, Br or I; ii) R 1 and R 2 are either methyl or H with the proviso that R 1 and R 2 are different from one another; iii) R 3 and R 4 are either methoxy or H with the proviso that R 3 and R 4 are different from one another; and iv) the group and/or the group in said different labeling reagents of said set of isotopically encoded isobaric labeling reagents is isotopically enriched with one or more heavy atom isotopes; and b) mixing two or more of the differentially labeled samples, or a portion thereof, and optionally one or more calibration standards to thereby produce a sample mixture.