A system for determining if a multiple reaction monitoring transition measurement for a compound of interest includes an interference, comprising: an ion source device that ionizes a compound of interest producing an ion beam of one or more precursor ions; a tandem mass spectrometer that includes a mass filter, a fragmentation device and a mass analyzer and receives the ion beam from the ion source device, wherein the mass filter is adapted to produce a mass selection window capable of resolving isotopes of precursor ions from the ion beam and wherein the tandem mass spectrometer is adapted to measure an intensity of an MRM transition by selecting a precursor ion of the MRM transition using the mass filter, fragmenting the precursor ion using the fragmentation device, and measuring an intensity of a product ion of the MRM transition using the mass analyzer; and a processor in communication with the tandem mass spectrometer, the processor configured to: instruct the tandem mass spectrometer to measure a first intensity of a first MRM transition that includes a first precursor ion and a first product ion, instruct the tandem mass spectrometer to measure a second intensity of a second MRM transition that includes a second precursor ion and the same first product ion as the first MRM transition, wherein the second precursor ion is an isotope of the first precursor ion, calculate a ratio of the first intensity to the second intensity, calculate a theoretical ratio of the quantity of first precursor ion to the second precursor ion according to their isotopic relationship, calculate a difference between the ratio and the theoretical ratio, compare the difference to a threshold value, and if the difference is less than the threshold value, identify the first intensity of the first MRM transition as not including an interference for the compound of interest. an ion source device that ionizes a compound of interest producing an ion beam of one or more precursor ions; a tandem mass spectrometer that includes a mass filter, a fragmentation device and a mass analyzer and receives the ion beam from the ion source device, wherein the mass filter is adapted to produce a mass selection window capable of resolving isotopes of precursor ions from the ion beam and wherein the tandem mass spectrometer is adapted to measure an intensity of an MRM transition by selecting a precursor ion of the MRM transition using the mass filter, fragmenting the precursor ion using the fragmentation device, and measuring an intensity of a product ion of the MRM transition using the mass analyzer; and a processor in communication with the tandem mass spectrometer, the processor configured to: instruct the tandem mass spectrometer to measure a first intensity of a first MRM transition that includes a first precursor ion and a first product ion, instruct the tandem mass spectrometer to measure a second intensity of a second MRM transition that includes a second precursor ion and the same first product ion as the first MRM transition, wherein the second precursor ion is an isotope of the first precursor ion, calculate a ratio of the first intensity to the second intensity, calculate a theoretical ratio of the quantity of first precursor ion to the second precursor ion according to their isotopic relationship, calculate a difference between the ratio and the theoretical ratio, compare the difference to a threshold value, and if the difference is less than the threshold value, identify the first intensity of the first MRM transition as not including an interference for the compound of interest. instruct the tandem mass spectrometer to measure a first intensity of a first MRM transition that includes a first precursor ion and a first product ion, instruct the tandem mass spectrometer to measure a second intensity of a second MRM transition that includes a second precursor ion and the same first product ion as the first MRM transition, wherein the second precursor ion is an isotope of the first precursor ion, calculate a ratio of the first intensity to the second intensity, calculate a theoretical ratio of the quantity of first precursor ion to the second precursor ion according to their isotopic relationship, calculate a difference between the ratio and the theoretical ratio, compare the difference to a threshold value, and if the difference is less than the threshold value, identify the first intensity of the first MRM transition as not including an interference for the compound of interest.