Patent ID: 7923257

Claim:
A method of detecting one or more molecular isomers of one or more branched-chain amino acids in a sample, the method comprising: derivatizing one or more molecular isomers of one or more branched-chain amino acids in a sample, wherein the sample comprises one or more molecular isomers of one or more branched-chain amino acids and a first standard, the first standard being a branched-chain amino acid labeled with one or more heavy atoms; adding to the sample, after derivatization, a nonderivatized or derivatized branched-chain amino acid that is labeled with one or more heavy atoms as a second standard; evaluating the sample using tandem mass spectrometry; and detecting peaks indicative of derivatized and nonderivatized forms of one or more branched-chain amino acids in the sample, thereby distinguishing between branched-chain amino acids that are molecular isomers in the sample.