TKO6: A Peptide Standard To Assess Interference for Unit-Resolved Isobaric Labeling Platforms

Protein abundance profiling using isobaric labeling is a well-established quantitative mass spectrometry technique. However, ratio distortion resulting from coisolated and cofragmented ions, commonly referred to as interference, remains a drawback of this strategy. Tribrid mass spectrometers, such as the Orbitrap Fusion and the Orbitrap Fusion Lumos with a triple mass analyzer configuration, facilitate methods (namely, SPS-MS3) that can help alleviate interference. However, few standards are available to measure interference and thereby aid in method development. Here we introduce the TKO6 standard that assesses ion interference and is designed specifically for data acquired at low (unit) mass resolution. We use TKO6 to compare interference in MS2- versus MS3-based quantitation methods, data acquisition methods of different lengths, and ion-trap-based tandem mass tag reporter ion analysis (IT-MS3) with conventional Orbitrap-based analysis (OT-MS3). We show that the TKO6 standard is a valuable tool for assessing quantification accuracy in isobaric-tag-based analyses.