Update contact information. Update publication information. We developed a multiplex pseudo-isobaric dimethyl labeling (m-pIDL) method for proteome quantification to extend the capacity of the fragment ion-based method to 6-plex by one-step dimethyl labeling with several millidalton and dalton mass differences between precursor ions and enlarging the isolation window of precursor ions to 10 m/z during data acquisition.