Abstract: A method for analyzing leucine and isoleucine for newborn mass-screening or similar tests by multiple reaction monitoring (MRM) measurements using a tandem mass spectrometer is provided. The method includes: a measurement step for acquiring intensity information of ions originating from leucine and isoleucine by performing, on a specimen, a first MRM measurement for at least one MRM transition selected from a group of m/z 132>69, m/z 132>57, m/z 132>56, m/z 132>43, m/z 132>41, m/z 132>39, m/z 132>30 and m/z 132>27 as well as a second MRM measurement for an MRM transition of m/z 132>86; and a processing step for discriminating whether the specimen contains leucine or isoleucine, or for determining a relative abundance of leucine and isoleucine in the specimen, based on a qualifier ion ratio which is a ratio between a signal intensity obtained by the first MRM measurement and a signal intensity obtained by the second MRM measurement.

Abstract: First and second MRM transitions for a target substance, a first reference value concerning a measured intensity of the first MRM transition, and a second reference value concerning the measured-intensity ratio between the first and second MRM transitions are set. MRM measurements of an analyte sample using the first and second MRM transitions are performed to obtain a first intensity of the first MRM transition and a second intensity of the second MRM transition (Steps 11 and 12). The value of the first intensity is compared with the first reference value to determine whether the target substance is possibly contained (first determination; Step 14). For a target substance considered to be possibly contained in the analyte sample, the ratio between the first and second intensities is compared with the second reference value to determine whether the target substance is contained (second determination; Step 18).

Abstract: One mode of a method for analyzing acylcarnitine according to the present invention is a method for analyzing C5 acylcarnitine using a tandem mass spectrometer, the method including: a measurement step of performing MRM measurement on a specimen according to at least one of MRM transitions of m/z 24>187, m/z 246>57, m/z 246>41, and m/z 246>29; and a processing step of distinguishing between isovalerylcarnitine and pivaloylcarnitine which is an isomer of isovalervicarnitine in the specimen or determining whether or not C5 acylcarnitine in the specimen includes pivaloylcarnitine, using a measurement result obtained in the measurement step. This makes it possible to satisfactorily distinguish between isovalerylcarnitine and pivaloylcarnitine, which have been conventionally difficult to distinguish.